A abampere (aA) The unit of electric current in the CGSeniu system, defined as that current that, if flowing through two parallel conductors of negligible cross section and infinite length, placed 1 cm apart in vacuo, would produce on each conductor a force of 1 dyne per centimeter of length. 1 abampere = 1 abcoulomb/s = r statampere (where c = speed of light in cm/s) = 10 ampere. aberration Imperfect image formation due to geometric imperfections in the optical elements of a system ablation 1 . The wasting of glacier ice by any process (calving, melting, evaporation, etc.). 2. The shedding of molten material from the outer sur- face of a meteorite or tektite during its flight through the atmosphere. absolute age The age of a natural substance, of a fossil or living organism, or of an artifact, obtained by means of an absolute dating method. See absolute dating method. absolute density Density in kg/m' or, more commonly, in g/cm\ both at STP. Cf. density, relative density abso
Magnetic Effects of Electric Current class 10 NCERT physics MCQ & SAQ
Magnetic Effects of Electric Current class 10 NCERT physics NCERT SOLUTION:
1. Why does a compass needle get deflected when brought near a bar magnet?
Answer
The needle of a compass is a small magnet. That’s why when a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle gets deflected.
Page No: 228
1. Draw magnetic field lines around a bar magnet.
Answer
Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.
2. List the properties of magnetic lines of force.
Answer
The properties of magnetic lines of force are as follows.
→ Magnetic field lines emerge from the north pole.
→ They merge at the south pole.
→ The direction of field lines inside the magnet is from the south pole to the north pole.
→ Magnetic lines do not intersect with each other.
3. Why don't two magnetic lines of force intersect each other?
Answer
The two magnetic field lines do not intersect each other because if they do it means at the point of intersection the compass needle is showing two different directions which is not possible.
Page No: 229
1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Inside the loop = Pierce inside the table
Outside the loop = Appear to emerge out from the table
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for the upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.
2. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer
The magnetic field lines inside a current-carrying long straight solenoid are uniform.
Page No: 230
3. Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current
(a) is zero
(b) decreases as we move towards its end
(c) increases as we move towards its end
(d) is the same at all points
► (d) is the same at all points
Page No: 231
1. Which of the following properties of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
► (c) velocity and (d) momentum
Page No: 232
2. In Activity 13.7 (page: 230), how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased: (ii) a stronger horse-shoe magnet is used: and (iii) length of the rod AB is increased?
The displacement of rod AB is increased due to magnetic force exerted on it, if :
(i) If the current in the rod is increased then the rod will be deflected with greater force.
(ii) If a stronger horse-shoe magnet is used then also the rod will be deflected with greater force due to the increase in magnetic field.
(iii) If the length of the rod AB is increased.
3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south
(b) towards east
(c) downward
(d) upward
► (d) upward
Page No: 233
1. State Fleming's left-hand rule.
Answer
Fleming's left hand rule states that if we arrange the thumb, the center finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the center finger gives the direction of current, and the forefinger points in the direction of magnetic field.
2. What is the principle of an electric motor?
Answer
The principle of an electric motor is based on the magnetic effect of electric current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is according to the Fleming’s left-hand rule.
3. What is the role of the split ring in an electric motor?
Answer
The split ring in the electric motor also known as a commutator reverses the direction of current flowing through the coil after every half rotation of the coil. Due to this the coil continues to rotate in the same direction.
Page No: 236
1. Explain different ways to induce current in a coil.
The different ways to induce current in a coil are as follows:
→ If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
→ If a magnet is moved relative to a coil, then an electric current is induced in the coil.
Page No: 237
1. State the principle of an electric generator.
Answer
Electric generator works on the principle of electromagnetic induction. Electricity is generated by rotating a coil inside a magnetic field.
2. Name some sources of direct current.
Answer
Some sources of direct current are cell, DC generator, etc.
3. Which sources produce alternating current?
Answer
AC generators, power plants, etc., produce alternating current.
4. Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution
► (c) half revolution
Page No: 238
1. Name two safety measures commonly used in electric circuits and appliances.
Answer
Two safety measures commonly used in electric circuits and appliances are
→ Electric Fuse: An electric fuse is connected in series; it protects the circuit from overloading and prevents it from short circuiting.
→ Proper earthing of all electric circuits in which any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.
2. An electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Current drawn by the electric oven can be obtained by the expression,
P = VI
Where,
Current = I
Power of the oven, P = 2 kW = 2000 W
Voltage supplied, V = 220 V
I = 2000/220 V = 9.09 A
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.
3. What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer
The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
→ Too many appliances should not be connected to a single socket.
→ Too many appliances should not be used at the same time.
→ Faulty appliances should not be connected in the circuit.
→ Fuse should be connected in the circuit.
Page No: 240
Exercise
1. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire
(b) The field consists of straight lines parallel to the wire
(c) The field consists of radial lines originating from the wire
(d) The field consists of concentric circles centered on the wire
► (d) The field consists of concentric circles centered on the wire
2. The phenomenon of electromagnetic induction is
(a) the process of charging a body
(b) the process of generating magnetic field due to a current passing through a coil
(c) producing induced current in a coil due to relative motion between a magnet and the coil
(d) the process of rotating a coil of an electric motor
► (c) producing induced current in a coil due to relative motion between a magnet and the coil
3. The device used for producing electric current is called a
(a) generator
(b) galvanometer
(c) ammeter
(d) motor
► (a) generator
4. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
► (d) AC generator has slip rings while the DC generator has a commutator.
5. At the time of short circuit, the current in the circuit
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously
► (c) increases heavily
6. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
► False
An electric motor converts electrical energy into mechanical energy.
(b) An electric generator works on the principle of electromagnetic induction.
► True
(c) The field at the center of a long circular coil carrying current will be parallel straight lines.
► True
(d) A wire with a green insulation is usually the live wire of an electric supply.
► False
Live wire has a red insulation cover, whereas earth wire has green insulation color in the domestic circuits.
7. List three sources of magnetic fields.
Answer
Three sources of magnetic fields are as follows:
→ Current-carrying conductors
→ Permanent magnets
→ Electromagnets
Page No: 241
8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Answer
A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure.
In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.
9. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
The force experienced by a current-carrying conductor is the maximum when the direction of current is perpendicular to the direction of the magnetic field.
10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer
The direction of the magnetic field is vertically downwards. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from the back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming's left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.
11. Draw a labeled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
Answer
Principle: It works on the principle of the magnetic effect of current. A current-carrying coil rotates in a magnetic field.
Working: When a current is allowed to flow through the coil MNST by closing the switch, the coil starts rotating anti-clockwise. This happens because a downward force acts on length MN and at the same time, an upward force acts on length ST. As a result, the coil rotates anti-clockwise.
Current in the length MN flows from M to N and the magnetic field acts from left to right, normal to length MN. Therefore, according to Fleming's left hand rule, a downward force acts on the length MN. Similarly, current in the length ST flows from S to T and the magnetic field acts from left to right, normal to the flow of current. Therefore, an upward force acts on the length ST. These two forces cause the coil to rotate anti-clockwise.
After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.
The current flows through the coil in the direction of TSNM. The reversal of current through the coil MNST repeats after each half rotation. As a result, the coil rotates unidirectional.
The split rings help to reverse the direction of current in the circuit. These are called the commutators.
12. Name some devices in which electric motors are used?
Answer
Some devices in which electric motors are Water pumps, Electric fans, Electric mixers and Washing machines.
13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Answer
(i) The needle of the galvanometer shows a momentary deflection in a particular direction.
(ii) The needle of the galvanometer shows a momentarily in the opposite direction.
(iii) The needle of the galvanometer shows no deflection.
14. Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give a reason.
Answer
Two circular coils A and B are placed close to each other. When the current in coil A is changed, the magnetic field associated with it also changes. As a result, the magnetic field around coil B also changes. This change in magnetic field lines around coil B induces an electric current in it. This is called electromagnetic induction.
15. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
Answer
(i) Maxwell's right hand thumb rule
(ii) Fleming's left hand rule
(iii) Fleming's right hand rule
16. Explain the underlying principle and working of an electric generator by drawing a labeled diagram. What is the function of brushes?
Answer
Principle: An electric generator works on the principle of electromagnetic induction phenomenon. According to it, whenever a coil is rotated between the poles of a magnet, an induced current is set up in the coil, whose direction is given by Fleming’s right hand rule.
Working: Let in the beginning, as shown in Fig. brushes B1 and B2 are kept pressed separately on rings R1 and R2 respectively. Let the axle attached to the rings is rotated such that arm AB of the coil moves up and arm CD moves down in the magnetic field. Due to rotation of arms AB and CD induced currents are set up in them. As per Fleming’s right hand rule induced currents in these arms are along the directions AB and CD. Thus an induced current flows along ABCD and current in the external circuit flows from B2 to B1.
After half a rotation, arm AB starts moving down and the arm CD upward. Therefore, directions of induced currents in these arms change. Thus net induced current now becomes DCBA. In the external circuit now current flows from B1 to B2. Thus after every half rotation current changes its direction and an alternating current is obtained from the generator.
Function of Brushes: Brushes are kept pressed on the two slip rings separately. Outer ends of the brushes are connected to the galvanometer (or the external load). Thus brushes help in transferring current from the coil ABCD to the external circuit.
17. When does an electric short circuit occur?
Answer
If the insulation of the wires used in the circuit is damaged or the appliance used is faulty due to which the live wire and the neutral wire comes in direct contact as a result current in the circuit rises and the short circuit occurs.
18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer
The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.
Magnetic Effects of Electric Current class 10 NCERT physics MCQ :
1. A device for producing electric current is called a
(a) Galvanometer
(b) Motor
(c) Generator
(d)Ammeter
► (c) Generator
2. Inside the magnet, the field lines moves
(a) from north to south
(b) from south the north
(c) away from south pole
(d) away from north pole
► (a) from north to south
3. Magnetic Effect of Electric Current Class 10 MCQ Question 1. Magnetic effect of current was discovered by
(a) Oersted
(b) Faraday
(c) Bohr
(d) Ampere
► (a) Oersted
4. By which instrument, the presence of magnetic field be determined?
(a) Magnetic Needle
(b) Ammeter
(c) Galvanometer
(d) Voltmeter
► (d) Voltmeter
5. The nature of magnetic field line passing through the center of current carrying circular loop is
(a) circular
(b) ellipse
(c) parabolic
(d) straight line
► (d) straight line
6. The magnetic field near a long straight wire is described by
(a) Straight field lines parallel to the wire.
(b) Straight field lines perpendicular to the wire.
(c) Connective circle centered on the wire.
(d) Radial field lines starting from the wire.
► (c) Connective circle centered on the wire.
7. The pattern of the magnetic field produced by the straight current carrying conducting wire is
(a) in the direction opposite to the current
(b) in the direction parallel to the wire
(c) circular around the wire
(d) in the same direction of current
► (a) in the direction opposite to the current
8. At the time of short circuit, the current in the circuit
(a) vary continuously
(b) reduced considerably
(c) increases heavily
(d) does not change
► (c) increases heavily
9. Which of the following properties of a proton can change when it moves freely in a
magnetic field
(a) mass
(b) speed
(c) velocity
(d) momentum
► (c) velocity
10. A positive charge is moving upwards in a magnetic field directed towards north. The particle will be deflected towards
(a) west
(b) north
(c) south
(d) east
► (a) west
11. A current carrying conductor placed in a magnetic field experiences a force. The
displacement of the conductor in magnetic field can be increased by
(a)Decreasing the magnetic field.
(b) Decreasing the current in the conductor.
(c) Increasing the magnetic field.
(d) None of the above.
► (c) Increasing the magnetic field.
12. The instrument that use to defect electric current in the circuit is known as
(a) electric motor
(b) A.C generator
(c) galvanometer
(d) none of the above
► (a) electric motor
13. Fleming’s left hand and Right hand rules are used in
(а) Generator and electric motor
(b) Electric motor and generator
(c) any rule can be used for any device
(d) both are not applied for generator and motor.
► (b) Electric motor and generator
14. A positively charged particle say an alpha particle projected towards west is
deflected toward north by a magnetic field. The direction of the magnetic field is
(a) Upward
(b) downward
(c) towards south
(d) towards east.
► (d) towards east.
15. Electric motor converts
(a) Mechanical energy into electrical energy
(b) Mechanical energy into heat energy
(c) Electrical energy into heat energy
(d) Electrical energy into mechanical energy
► (d) Electrical energy into mechanical energy
16. In electric motor, to make the coil rotating continuously in the same direction, current is reversed in the coil after every half rotation by a device called
(a) carbon brush
(b) commutator
(c) slip ring
(d) armature
► (b) commutator
17. Which of the following factors affect the strength of force experienced by a current carrying conduct in a uniform magnetic field?
(a) magnetic field strength
(b) magnitude of current in a conductor
(c) length of the conductor within magnetic field
(d) All of above
► (d) All of above
18. The factors on which one magnetic field strength produced by current carrying solenoids depends are
(a) Magnitude of current
(b) Number of turns
(c) Nature of core material
(d) All of the above
► (d) All of the above
19. Potential difference between a live wire and a neutral wire is
(a) 200 volt
(b) 150 volt
(c) 210 volt
(d) 220 volt
► (d) 220 volt
20. When current is parallel to magnetic field, then force experience by the current carrying conductor placed in uniform magnetic field is
(a) Twice to that when angle is 60°
(b) Thrice to that when angle is 60°
(c) zero
(d) infinite
► (a) Twice to that when angle is 60°
21. Small current in a circuit is detected by
(a) Galvanometer
(b) Solenoid
(c) Voltmeter
(d) Fleming’s left hand rule
► (a) Galvanometer
22. In the domestic electric circuits, the red coloured insulated copper wire is called
(a) Neutral wire
(b) Fuse wire
(c) Live wire
(d) Earthing wire
► (c) Live wire
23. The most important safety device method used for protecting electrical appliances
from short circuiting or overloading is
(a) Earthing
(b) use of stabilizer
(c) use of electric meter
(d) fuse
► (d) fuse
24. A soft iron bar is introduced inside the current carrying solenoid. The magnetic field inside the solenoid
(a) will decrease
(b) will remains same
(c) will increase
(d) will become zero
► (c) will increase
25. A.C generator works on the principle of
(a) force experience by a conductor in magnetic field
(b) electromagnetic induction
(c) electrostatic
(d) force experienced by a charge particle in an electric field.
► (a) force experience by a conductor in magnetic field
26. A D.C generator works on the principle of
(a) ohno's law
(b) Joule’s law of heating
(c) Faraday's law of electromagnetic induction.
(d) none of the above
► (c) Faraday's law of electromagnetic induction.
27. Which of the following statements is not correct about the magnetic field?
(a) Magnetic field lines form a continuous closed curve.
(b) Magnetic field lines do not interest each other.
(c) Direction of tangent at any point on the magnetic field line curve gives the direction of magnetic field at that point.
(d) Outside the magnet, magnetic field lines go from the South to the North pole of the magnet.
► (d) Outside the magnet, magnetic field lines go from the South to North pole of the magnet.
28. A current through a horizontal power line flows from south to North direction. The direction of magnetic field line 0.5m above it is
(a) North
(b) South
(c) West
(d) East
► (a) North
29. Direction of rotation of a coil in electric motor is determined by
(a) fleming’s right hand rule
(b) fleming’s left hand rule
(c) faraday law of electromagnetic inductors
(d) None of above
► (b) fleming’s left hand rule
30. Forces acting on a stationary charge of in the magnetic field B is
(a) BQ v
(b) BQ/v
(c) Bv/Q
(d) zero
► (d) zero
31. The condition for the praenomen of electromagnetic induction is that there must be a relative motion between
(a) the galvanometer and magnet
(b) the coil of wire and galvanometer
(c) the coil of wire and magnet
(d) the magnet and galvanometer
► (c) the coil of wire and magnet
32. We can induce the current in a coil by
(a) moving the coil in a magnetic field
(b) by changing the magnetic field around it
(c) by changing the orientation of the coil in the magnetic field
(d) All of above
► (a) moving the coil in a magnetic field
33. The rectangular coil of copper wires is rotated in a magnetic field. The direction of
induced current change once in each
(a) one revolution
(b) one fourth revolution
(c) half revolution
(d) two revolutions
► (b) one fourth revolution
34. If the current values periodically from zero to a maximum value, back to zero and then reverses its direction, the current is
(a) direct
(b) alternative
(c) pulsating
(d) none of the above
► (b) alternative
35. The main advantage of A.C power transmission over D.C power transmission over’ long distance is
(a) AC transmit without much loss of energy
(b) less insulation problem
(c) less problem of instability
(d) easy transformation.
► (a) AC transmit without much loss of energy
36. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is:
(a) towards south
(b)towards east
(c) downward
(d) upward
► (d) the direction of the magnetic field is vertically upward.
37. The strength of magnetic field inside a long current carrying straight solenoid is
(a) more at the ends than at the center
(b) minimum in the middle
(c) same at all points
(d) found to increase from one end to the other
► (c) same at all points
38. The most important safety method used for protecting home appliances from short circuiting or overloading is
(a) earthing
(b) use of fuse
(c) use of stabilizers
(d) use of electric meter
► (b) use of fuse
39. Which one of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire
(c) The field consists of radial lines originating from the wire
(d) The field consists of concentric circles centered on the wire
► (d) The field consists of concentric circles centered on the wire.
40. To convert an AC generator into DC generator
(a) split-ring type commutator must be used
(b) slip rings and brushes must be used
(c) a stronger magnetic field has to be used
(d) a rectangular wire loop has to be used
► (a) split-ring type commutator must be used
41. Overloading is due to
(a) Insulation of wire is damaged
(b) fault in the appliances
(c) accidental hike in supply voltage
(d) All of the above
► (d) All of the above
42. The device used for producing electric current is called
(a) generator
(b) galvanometer
(c) ammeter
(d) motor
► (a) generator
43. Commercial electric motors do not use
(a) an electromagnet to rotate the armature
(b) effectively large number of turns of conducting wire in the current carrying coil
(c) a permanent magnet to rotate the armature
(d) a soft iron core on which the coil is wound
► (c) a permanent magnet to rotate the armature
44. Who has stated the Right hand Thumb Rule?
(a) Orsted
(b) Fleming
(c) Einstein
(d) Maxwell
► (d) Maxwell
45. The essential difference between A.C. generator and a D.C. generator is that
(a) A.C. generator has an electromagnet while a D.C. generator has permanent magnet.
(b) D.C. generator will generate a higher voltage
(c) A.C. generator will generate a higher voltage
(d) A.C. generator has slip rings while the D.C. generator has commentators.
► (d) A.C. generator has slip rings while the D.C. generator has commentators.
46. What should be the core of an electromagnet?
(a) soft iron
(b) hard iron
(c) rusted iron
(d) none of above
► (a) soft iron
47. Which device produces the electric current?
(a) generator
(b) galvanometer
(c) ammeter
(d) motor
► (a) generator
48. Magnetic lines of force inside current carrying solenoid are
(a) perpendicular to the axis.
(b) along the axis and are parallel to each other.
(c) parallel inside the solenoid and circular at the ends.
(d) circular.
► (c) parallel inside the solenoid and circular at the ends.
49. Assertion: Strength of an electromagnet depends on the magnitude of current flowing through them.
Reason: Electromagnets are majorly used for lifting heavy weights.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (b) Both A and R are true but R is not the correct explanation of A.
50. Assertion: Steel core is used as an electromagnet.
Reason: Steel gets permanently magnetized when the current flows through the coil wound around.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (d) A is false but R is true.
51. Assertion: It is fatal to touch a live electric wire as the person gets a severe electric shock. In some cases, electric shock can even kill a person.
Reason: The electric current passes through the body to the earth forming a circuit and bums the blood.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (a) Both A and R are true and R is the correct explanation of A.
Magnetic Effects of Electric Current class 10 NCERT physics SAQ:
Q.1. Two circular coils P and Q are kept close to each other, of which coil P carries a current. What will you observe in the galvanometer connected across the coil Q,
(a) if current in the coil P is changed?
(b) if both the coils are moved in the same direction with the same speed?
Give reason to justify your answer in each case. [CBSE 2011, 2019]
Ans. (a) If current in the coil P [Fig. 13.24] is increased, we get momentary deflection in the galvanometer connected across the coil Q in one direction. However, if current in the coil P is decreased, the deflection in the galvanometer is in the opposite direction. Due to change of current in coil P, the magnetic field of coil Q also changes and so induced current is set up in coil Q and the galvanometer shows a deflection.
(b) If both the coils P and Q are moved in the same direction with the same speed, the magnetic field of both the coils remain unchanged. Hence no induced current is set up in coil Q and there is no deflection in the galvanometer.
Q.2. What is the function of a galvanometer in a circuit? [CBSE 2019]
Ans. A galvanometer is used to detect the flow of current, if any, in a circuit.
Q.3. One of the major causes of fire in office buildings is short-circuiting. List three reasons which may lead to short-circuiting. How can it be prevented? [CBSE2016]
Ans. Three possible reasons of short-circuiting of an electrical circuit are as follows:
The insulation of electrical wiring is damaged.
The electrical appliance used in the circuit is defective.
An appliance of higher power rating is being run on an electrical line of lower power rating.
Short-circuiting can be prevented by the use of an electrical fuse of appropriate capacity.
Q.4. What is an electric fuse ? Briefly describe its function. [CBSE 2010,2011,2012,2013]
Or
Explain the use of an electrical fuse. What type of fuse material is used for fuse wire and why? [CBSE 2013,2014,2016]
Ans. An electric fuse is a device that is used ahead of and in series of an electric circuit as a safety device to prevent the damage caused by short-circuiting or overloading of the circuit.
It is a small, thin wire of a material whose melting point is low. Generally, wire of tin or tin-lead alloy of tin-copper alloy is used as a fuse wire. If, due to some fault, the electric circuit gets short-circuited, then a strong current begins to flow. Due to such a strong flow of current, the fuse wire is heated up and gets melted. As a result, the electric circuit is broken and current flow stops. Thus, possible damage to the circuit and appliances is avoided.
Q.5. (a) List four factors on which the magnitude of magnetic force acting on a moving charge in a magnetic field depends.
(b) How will a fine beam of electrons streaming in west to east direction be affected by a magnetic field directed vertically upwards? Explain with the help of a diagram mentioning the rule applied. [CBSE 2014, 2016]
Ans. (a) The magnitude of the magnetic force acting on a moving charge in a magnetic field depends on:
the magnitude of charge
speed of moving charge
strength of magnetic field
the angle between the direction of motion of charge and the direction of magnetic field.
(b) The electron streaming from west to east is equivalent to a current from east to west. The magnetic field B is vertically upwards and shown by cross marks (x). Hence, in accordance with Fleming’s left-hand rule, the electron will experience a force in the north direction and be deflected in that direction.
Q.6. What is a solenoid? Draw magnetic field lines due to a current-carrying solenoid. Write three important features of the magnetic field obtained. [CBSE 2010, 2011, 2012, 2014, 2015, 2016]
Ans. A solenoid is a coil of a large number of circular turns of wire wrapped in the shape of a cylinder. On passing electric current, a magnetic field is developed. Magnetic field lines are drawn below. The field is along the axis of solenoid such that one end of the solenoid behaves as north pole and the other south pole. Thus, the field of a solenoid is similar to that of a bar magnet.
Important features of magnetic field due to a current-carrying solenoid are:
Magnetic field lines inside the solenoid are nearly straight and parallel to its axis. It shows that the magnetic field inside a solenoid is uniform.
Magnetic field of solenoid is identical to that due to a bar magnet with one end of the solenoid behaving as a north pole and the other end as a south pole.
A current-carrying solenoid exhibits the directive and attractive properties of a bar magnet.
Q.7. Describe an activity with a neat diagram to demonstrate the presence of magnetic field around a current-carrying straight conductor. [CBSE 2010, 2012, 2014, 2016]
Ans.
Take a long straight thick copper wire and insert it through the center of a plain cardboard. Cardboard is fixed so that it is perfectly horizontal and the thick wire is in vertical direction.
Prepare an electric circuit consisting of a battery, a variable resistance, an ammeter and a plug key.
Connect the copper wire in the circuit between the points X and Y. Sprinkle some iron filings uniformly on the cardboard. Put the plug in key K so that a current flows in the circuit.
Gently tap the cardboard using a finger. We observe that the iron filings align themselves forming a pattern of concentric circles around the copper wire.
These concentric circles represent the magnetic field lines. Direction of field lines is determined by the use of a compass needle. If current is flowing vertically downward then the magnetic field lines are along clockwise direction. If current is flowing vertically upward then the field lines are along an anticlockwise direction.
Q.8. (a) Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another pole. [CBSE 2012, 2014, 2016]
(b) What does the degree of closeness of field lines represent?
Ans. (a) Take a bar magnet and place it on a sheet of white paper fixed on a drawing sheet. Mark the boundary of the magnet. Take a small compass and place it near the north pole of the magnet. Mark the position of two ends of the compass needle. Move the needle to a new position so that its south pole occupies the position previously occupied by its north pole. In this way proceed step by step till we reach the south pole of the magnet. Join the points marked on the paper by a smooth curve. This curve represents a magnetic field line as shown in Fig. 13.15.
(b) The degree of closeness of magnetic field lines signifies the strength of magnetic field.
Q.9. What type of current is given by a cell? [CBSE 2011, 2012, 2014, 2016]
Ans. Direct current (D.C.).
Q.10. Write any one method to induce current in a coil. [CBSE 2014, 2016]
Ans. Whenever the magnetic field around a coil is changed, a current is induced in the coil.
Q.11. Under what condition is the force by a current-carrying conductor placed in a magnetic field maximum? [CBSE 2009, 2012, 2016]
Ans. The force acting on a current-carrying conductor placed in a magnetic field is maximum when the direction of current is at right angles to the direction of the magnetic field.
Q.12. Define the magnetic field of a bar magnet. [CBSE 2006,2010,2014,2015,2016]
Ans. The magnetic field of a bar magnet is the region around the magnet in which force due to the magnet can be felt.
Q.13. What is the shape of magnetic field lines due to a straight current-carrying conductor? [CBSE 2010,2013,2014,2015]
Ans. Magnetic field lines form concentric circles around the conductor with conductor at the center.
Q.14. What are magnetic field lines? [CBSE 2010,2011,2012,2015]
Ans. A magnetic field line around a magnet is the path along which the north pole of a magnetic compass needle points. A magnetic field line gives the direction of the magnetic field at a point.
Q.15. (a) Describe an activity to show that an electric current-carrying wire behaves like a magnet.
(b) Write the rule which determines the direction of magnetic hold developed around a current-carrying straight conductor. [CBSE 2010, 2011, 2012, 2014, 2015]
Ans. (a) Take a straight, thick copper wire X Y and connect it to an electric circuit consisting of a battery, key and resistor. Place a small compass near the copper wire. Now put the plugin key K so that a current begins to flow. The compass needle is deflected.
It shows that the current-carrying copper wire is behaving like a magnet.
(b) The direction of the magnetic field around a straight current-carrying conductor is given by the “right-hand thumb rule”. According to the rule, imagine holding the current-carrying straight conductor in your right hand such that the thumb points towards the direction of the current. Then the fingers of the right hand wrap around the conductor in the direction of the field lines of the magnetic field.
Q.16. Out of the three wires live, neutral or earth, which one goes through the ON/ OFF switch? [CBSE 2010, 2012, 2014, 2015]
Ans. The live wire.
Q.17. Why does a current-carrying conductor experience a force when it is placed in a magnetic field? [CBSE 2011, 2015]
Ans. A current-carrying conductor produces a magnetic field around it. This magnetic field interacts with the externally applied magnetic field and as a result the conductor experiences a force.
Q.18. What is the frequency of A.C. being supplied in our houses? [CBSE 2010, 2013, 2015]
Ans. 50 Hz.
Q.19. Distinguish between a direct current and an alternating current. [CBSE 2012, 2013, 2014, 2015]
Ans.
Q.20. Describe an activity to explain how a moving magnet can be used to generate electric current in a coil. [CBSE 2012,2014,2015]
Or
A coil made of insulated copper wire is connected to a galvanometer. What will happen to the deflection of the galvanometer if a bar magnet is pushed into the coil and then pulled out of it? Give reason for your answer and name the phenomenon involved. [CBSE 2010,2011,2012]
Ans. Take a coil AB of insulated copper wire having a number of turns. Connect the ends of the coil to a sensitive galvanometer G. Now take a bar magnet NS and rapidly bring the magnet towards the end B of coil as shown in Fig. 13.23.
The galvanometer gives momentary deflection in one direction. Now take the magnet away from the coil, the galvanometer again gives momentary deflection but in the opposite direction. It clearly shows that motion of the magnet induces a current in the coil.Again keep the magnet fixed and gently move the coil AB either towards the magnet or away from the magnet. We get deflection in the galvanometer even now. Thus, an induced current is produced in a coil whenever there is relative motion between the coil and the magnet. This phenomenon is known as electromagnetic induction.
Q.21. A metallic conductor is suspended perpendicular to the magnetic field of a horse-shoe magnet. The conductor gets displaced towards the left when a current is passed through it. What will happen to the displacement of the conductor if the :
(i) current through it is increased?
(ii). a horse-shoe magnet is replaced by another stronger horse-shoe magnet?
(iii) direction of current through it is reversed ? [CBSE 2011, 2012, 2015]
Ans. (i) On increasing the current flowing through metallic conductor, the force experienced by it is proportionately increased because F ∝ I.
(ii) On using a stronger horse-shoe magnet the magnetic force increases because F
(iii) On reversing the direction of current the direction of force is reversed and the conductor is displaced towards the right instead of the left direction.
Q.22. For the current carrying solenoid as shown below, draw magnetic field lines and give reason explaining that out of the three points A, B and C at which point the field strength is maximum and at which point it is minimum. [CBSE 2015]
Ans. Outside the solenoid magnetic field is minimum. At the ends of solenoid, magnetic field strength is half that of inside it. So Minimum - at point B; Maximum - at point A
Q.23. What is meant by solenoid? How does a current carrying solenoid behave? Give its main use. [CBSE 2015]
Ans. Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e. cardboard etc.) such that its length is greater than its diameter is called solenoid.When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence the current carrying solenoid behaves like a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.
Q.24. What are magnetic field lines? Justify the following statements
(a) Two magnetic field lines never intersect each other. [CBSE 2014]
(b) Magnetic field lines are closed curves. [CBSE 2015]
Ans. Magnetic field lines: It is defined as the path along which the unit North pole (imaginary) tends to move in a magnetic field if free to do so.
(a) The magnetic lines of force do not intersect (or cross) one another. If they do so then at the point of intersection, two drawn tangents at that point indicate that there will be two different directions of the same magnetic field, i.e. the compass needle points in two different directions which is not possible.
(b) Magnetic field lines are closed continuous curves. They emerge from the north pole of a bar magnet and go into its south pole. Inside the magnet, they move from the south pole to the north pole.
Magnetic Effects of Electric Current class 10 NCERT physics long question:
Q.1. Draw magnetic field lines produced around a current carrying straight conductor passing through a cardboard. Name, state and apply the rule to mark the direction of these field lines. How will the strength of the magnetic field change when the point where the magnetic field to be determined is moved away from the straight conductor? Give reason to justify your answer. [Allahabad 2019]
Ans.
Right-Hand Thumb Rule. This rule is used to find the direction of the magnetic field due to a straight current-carrying wire.
It states that if we hold the current-carrying conductor in the right hand in such a way that the thumb is stretched along the direction of the current, then the curly finger around the conductor represents the direction of the magnetic field produced by it.
Using compass needles, we can determine the strength of the magnetic field at various points. If the needle is moved away from the straight wire carrying constant current, the deflection in the needle decreases. It implies that magnetic field strength decreases as the distance increases.
Q.2. (a) What are magnetic field lines? How is the direction of magnetic field at a point in a magnetic field determined using field lines?
(b) Two circular coils 'X' and 'Y' are placed close to each other. If the current in the coil 'X' is changed, will some current be induced in the coil 'Y'? Give a reason.
(c) State 'Fleming's right hand rule. [CBSE 2018C]
Ans. (a) It is defined as the path along which the hypothetical unit N-pole tends to move in a magnetic field, if free to do so.
By drawing a tangent at that point on the magnetic field lines one can find the direction of the magnetic field at that point.
(b) Yes, if the current in coil X is changed, the magnetic field associated with it also changes around the coil 'Y' placed close to 'X'. This change in magnetic field lines linked with 'Y', according to Faraday law of electromagnetic induction, induces a current in the coil Y.
(c) Right-Hand Thumb Rule. This rule is used to find the direction of the magnetic field due to a straight current carrying wire.
It states that if we hold the current carrying conductor in the right hand in such a way that the thumb is stretched along the direction of current, then the curly finger around the conductor represents the direction of the magnetic field produced by it. This is known as the right-hand thumb rule.Direction of Field Lines due to current carrying straight conductor as shown in figure.Q.3. (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature
(ii) Brushes
(iii) Split ring [CBSE 2018]
Ans. (a) Fleming’s Left-Hand Rule: Stretch the thumb, forefinger and middle finger of the left hand such that they are mutually perpendicular to each other. If the forefinger is pointed towards the direction of magnetic field and middle finger in the direction of current, then the thumb will indicate the direction of motion or force experienced by the conductor. It is to be applied only when the current and magnetic field, both are perpendicular to each other.
(b) Principle of an electric motor: It works on the principle of magnetic effect of current. When a current carrying conductor is placed perpendicular to the magnetic field, it experiences a force. The direction of this force is given by Fleming’s left hand rule.
(c) (i) Armature: It consists of a large number of turns of insulated current-carrying copper wires wound over a soft iron core and rotated about an axis perpendicular to a uniform magnetic field supplied by the two poles of permanent magnet.
(ii) Brushes: Two conducting stationary carbon or flexible metallic brushes constantly touch the revolving split rings or commutator. These brushes act as a contact between the commutator and terminal battery.
(iii) Split ring: The split ring acts as a commutator in an electric motor. With the help of a split ring, the direction of current through the coil is reversed after every half of its rotation and the direction of currents in both the arms of the rotating coil remains the same. Therefore, the coil continues to rotate in the same direction.
Q.4. A current-carrying conductor is placed in a magnetic field. Now answer the following :
(i) List the factors on which the magnitude of force experienced by the conductor depends.
(ii) When is the magnitude of this force maximum?
(iii) If initially this force was acting from right to left, how will the direction of force change, if :
(a) direction of magnetic field is reversed?
(b) direction of current is reversed? [CBSE 2016]
Ans. (i) The magnitude of force experienced by the current-carrying conductor when placed in a magnetic field depends on current flowing, length of the conductor, the strength of magnetic field, orientation of conductor in the magnetic field.
(ii) Magnitude of force is maximum when current-carrying conductor is placed at right angles to the direction of magnetic field.
(iii) (a) Direction of force is reversed, that is now the force acts from left to right.
(b) Direction of force is reversed, that is now the force acts from left to right.
Q.5. In our daily life, we use two types of electric current whose current-time graphs are given in Fig. 13.29.
(i) Name the type of current in two cases.
(ii) Identify any one source for each type of current.
(iii) What is the frequency of current in case
(iv) in our country?
(v) Out of the two, which one is used in transmitting electric power over long distances and why? [CBSE 2011, 2014, 2015].
Fig (a)Fig (b)
Ans. (i) Currently shown in Fig. (a) is direct current (D.C.) but current shown in Fig. (b) is an alternating current (A.C.).
(ii) A cell/battery produces D.C. but an A.C. generator produces A.C.
(iii) In India the frequency of A.C. is 50 Hz.
(iv) A.C. is used in transmitting electric power over long distances. It is so because transmission loss of electric power can be minimized for A.C. by employing suitable transformers at generating stations and consuming centers.
Q.6. A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the center of it. He sprinkles some iron filings uniformly around the bar magnet. Then he taps the board gently.
Now answer the following questions :
(i) What does the student observe? Draw a diagram to illustrate your answer.
(ii) Why do the iron filings arrange in such a pattern?
(iii) What does the crowding of the iron filings at the ends of the magnet indicate? [CBSE 2015]
Ans.
(i) The student observes the magnetic field due to the given bar magnet. The pattern of the magnetic field is shown here.
(ii) There is a magnetic field around the given bar magnet. The iron filings experience a force due to the magnetic field and thus align themselves along the magnetic field lines.
(iii) The crowding of the iron filings at the ends of the magnet indicates the position of two magnetic poles N and S of a given bar magnet.
Comments
Post a Comment