CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma
CBSE CLASS XII
Electromagnetic Induction
(Q.2) If the magnetic field is parallel to a surface, then the magnetic flux through the surface is ( 1 mark )
(Q.3) What is the basic requirement to induce the electric current in a coil ? ( 1 mark )
(Q.4) Figure shows a straight wire placed between the pole pieces of a magnet. Induced emf will be developed across the ends of the wire, when it is moved towards (H) ( 1 mark )
(a) N.
(b) S.
(c) P.
(d) Q.(Q.5) The magnetic flux linked with a coil varies with time as Ф = 3t2 + 4t + 9 weber. What is the induced emf at t = 2 ? (H) ( 1 mark )
(Q.6) What is motional emf? ( 1 mark )
(Q.7) What is the basic principle of Lenz’s Law. ( 1 mark )
(Q.8) What is one Henry? ( 1 mark )
(Q.9) When the number of turns of a coil per unit length is doubled, its self inductance is ( 1 mark )
(Q.10) The induced emf of 2V is generated when the current in the circuit changes from 4A to 5A in one millisecond. Self inductance of the circuit is ( 1 mark )
(Q.11) A proton moving with velocity 10 km/s enters a region of space having a constant magnetic induction 5T. The largest deflecting force experienced by the particles (H) ( 1 mark )
(Q.12) Two coils are wound on the same iron rod so that the flux generated by one also passes through the other. The primary has 100 loops and secondary has 200 loops. When a current of 2 A flows through the primary the flux in it is 25 x 10–4Wb. The value of M between the coils is (H) ( 1 mark )
(Q.13) A magnet is moved towards a coil (i) quickly and then (ii) slowly, the induced emf is ( 1 mark )
(a) Larger in case (i)
(b) Larger in case (ii)
(c) Equal in both cases
(d) No emf is induced(Q.14) Which of the following instruments do not make use of eddy currents ? ( 1 mark )
(a) Electrical brakes.
(b) Induction motor.
(c) Transformer.
(d) Dead beat galvanometer.(Q.16) What happens to the magnetic flux when magnet and loop are moving with same velocity and in the same direction. ( 1 mark )
(Q.17) What is the basic cause of induced emf? ( 1 mark )
(Q.18) A cylindrical bar magnet is kept along the axis of a circular coil. Will there be a current induced in the coil if the magnet is rotated about its axis? (H) ( 1 mark )
(Q.19) A closed loop of wire is being moved so that it remains in a uniform magnetic field. What is the current induced? ( 1 mark )
(Q.20) A magnetic field of 20 T acts at right angles to a coil of area 20 cm2 with 50 turns.The coil is removed from the field in What is the change in magnetic flux and induced emf ? (H)(1mark )
(Q.21) A copper rod moves parallel to the horizontal direction. The induced emf developed across its ends due to earth’s magnetic field will be maximum at the ( 1 mark )
(Q.22) A conductor rod AB moves parallel to X-axis in uniform magnetic field, pointing in the positive X-direction. The end A of the rod gets (H)
( 1 mark )
(a) Positively charged.
(b) Negatively charged.
(c) Neutral.
(d) First positively charged and then negatively charged.(Q.23) A cylindrical bar magnet is kept along the axis of a circular coil. On rotating the magnet about its axis the coil will have induced, ( 1 mark )
(Q.24) In which of the following cases, with a bar magnet and the solenoid, no induced emf is produced. ( 1 mark )
(a) When magnet is inserted in the coil.
(b) When magnet is withdrawn from the coil.
(c) When coil is moved towards or away from the magnet.
(d) When the relative velocity of the coil w.r.t. the magnet is zero.(Q.25) The induced emf in a coil rotating in a magnetic field is maximum when the angle between the plane of the coil and the direction of field is ( 1 mark )
(Q.26) Which of the following phenomenon makes use of the electromagnetic induction? (1mark )
(a) Charging a storage battery
(b) Magnetizing an iron piece with a bar magnet
(c) Generation of hydroelectricity
(d) Magnetizing a soft iron piece by placing inside a current carrying solenoid(Q.27) In a uniform magnetic field of induction B a wire in the form of a semicircle of radius r rotates about the diameter of the circle with an angular frequency . The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R, the mean power generated per period of rotation is (H) ( 1 mark )
(Q.28) What is the expression for mutual inductance of two co-axial soleniods of same length and same area of cross section? ( 1 mark )
(Q.29) A uniform magnetic field is at right angles to the direction of motion of protons. As a result, the protons describe a circular path of radius 2.5 cm. If speed of the protons is doubled, then the radius of the circular path will be ( 1 mark )
(a) 0.5 cm
(b) 2.5 cm
(c) 5 cm
(d) 7.5 cm(Q.30) A horizontal telegraph wire 0.5 km long running east and west in a part of a circuit whose resistance is 2.5 W. The wire falls to the ground 5 m below. If g = 10m/s2 and B = 2 × 10-5 weber/m2, then the current induced in the circuit is, (H) ( 1 mark )
(a) 0.7 amp.
(b) 0.04 amp.
(c) 0.02 amp.
(d) 0.01 amp.(Q.31) A copper rod of length l is rotated about one end perpendicular to the uniform magnetic field B with constant angular velocity w. The induced e.m.f. between two ends is (H) ( 1 mark )
(a) 1/2 . B w l2
(b) 3/2 . B w l2
(c) 1. B w l2
(d) 2 . B w l2(Q.32) A small bar magnet is being slowly inserted with constant velocity inside a solenoid as shown in figure. Which graph best represents the relationship between emf induced with time is (H)
( 1 mark )
(a)
(b)
(c)
(d)
(Q.33) A long solenoid having 200 turns per cm carries a current of 1.5 amp. At the centre of it is placed a coil of 100 turns of cross-sectional area 3.14 × 10–4m2having its axis parallel to the field produced by the solenoid. When the direction of current in the solenoid is reversed within 0.05 sec, the induced em.f. in the coil is, (H) ( 1 mark )
(a) 0.48 V
(b) 0.048 V
(c) 0.0048 V
(d) 48 V(Q.34) A wire of length 0.1 m moves with a speed of 10 m/s perpendicular to a magnetic field of induction 1 Wb/m2. What is the e.m.f.? (H) ( 1 mark )
(a) 1 volt
(b) 2 volt
(c) 0.5 volt
(d) 1.5 volt(Q.35) A coil of inductance 0.5 H is connected to a 18 volt battery. What is the rate of growth of current? ( 1 mark )
(a) 23 A/s
(b) 24 A/s
(c) 28 A/s
(d) 36 A/s(Q.36) Two inductors of inductance L each are connected in series with opposite magnetic fluxes. What is the resultant inductance? ( 1 mark )
(a) 2L
(b) L
(c) Zero
(d) 3L(Q.37) A train is moving in the North-South direction with a speed of 72 km/hr. Find the amount of emf generated between two wheels, if the length of axle be 2m. Assume that the vertical component of earth’s field is 8x10-5wbm-2. (H) ( 2 Marks )
(Q.38) A coil is removed from a magnetic field (a) rapidly (b) slowly. In which case , more work will be done? ( 2 Marks )
(Q.39) In an AC generator a coil with N turns, all of the same area A and total resistance R, rotates with frequency W in a magnetic field B. Find the maximum value of emf in the coil. ( 2 Marks )
(Q.40) A metal conductor of length 1m rotates vertically about one of its ends at angular velocity 5 rad/sec. If the horizontal component of earth’s magnetic field is 0.2 x 10-4 T, then find the emf developed between the two ends of the conductor. (H) ( 2 Marks )
(Q.41) Define eddy currents. What is its disadvantage? ( 2 Marks )
(Q.42) Find the mutual inductance of two coils with number of turns 500 and 200 each of length 1m and cross-sectional area 4x10-4m2. ( 2 Marks )
(Q.43) Find the self induced emf in a 0.4H coil when the current in it is changing at the rate of 800A/S. ( 2 Marks )
(Q.44) A coil of area 10cm2 has 200 turns. Magnetic field of strength 0.1wb/m2s is perpendicular to the coil. The field is reduced to zero in 0.1s, then find the inducd emf in the coil. ( 2 Marks )
(Q.45) The magnitude of electric current is increasing from A towards B. If there is any induced current in the loop as shown in the fig what will be its direction?
( 3 Marks )
(Q.46) A magnetic field perpendicular to the plane of a rectangular frame of wire is concentrated about O. If the field decreases, will there be any emf induced in the loop 1?In the loop 2? ( 3 Marks )
(Q.47) An electron moves in a circle with uniform speed in a stationary magnetic field normal to the plane of the circle. If the field magnitude is made to increase with time, will the electron speed up or speed down? Will it continue to revolve in the same circle? ( 3 Marks )
(Q.48) A magnet is dropped down a long vertical copper tube. What will happen to its ultimate motion? ( 3 Marks )
(Q.49) An inductor coil of inductance 1H stores 32 J of magnetic field energy and dissipates energy as heat at the rate of 640w. Find the resistance if this is joined across a battery. ( 3 Marks )
(Q.50) When the current changes from +2A to –2A in 0.05 second, an emf of 8 volt is induced in a coil. Find the co-efficient of self induction of the coil. (H) ( 3 Marks )
(Q.51) Explain, whether an induced current will be developed in a conductor, if it is moved in a direction parallel to magnetic field. ( 3 Marks )
(Q.52) Calculate the rate at which the flux linked with the generated area changes with time when a rod of length l is
(a) translated
(b) rotated in a uniform magnetic field B as shown in the fig. (H)
( 5 Marks )
(Q.53) An air-cored solenoid with length 30cm, area of cross-section 25cm2 and number of turns 500 carries a current of 2.5A. The current is suddenly switched off in a brief time of 10-3s. How much is the average back emf induced across the ends of the open switch in the circuit? (H) ( 5 Marks )
(Q.54) A train is moving with speed 72km/hr on a rail track separated by distance 120cm and vertical component of earth’s magnetic field is 3x10-4T. Find
a) the average emf induced across the width of the train
b) if the resistance between the rails is 100 ohm.Find the retarding force on the train due to the magnetic field. (H) (5 Marks )(Q.55) A 0.2m long copper wire with its length parallel to x-axis moves along Y-axis with a constant velocity of 4m/sec in a region where a magnetic field of induction 0.05 Wb/m2 is present, which is pointing parallel to Z-axis. If the two ends of the wire are connected to a resistance of 2ohm,calculate. (H)
a) the emf developed between the two ends of the copper wire.
b) The current in the circuit.
c) The force required to keep the wire moving.
d) The rate at which work is done by the applied force.
e) The rate at which heat is produced. ( 5 Marks )(Q.56) The figure shows a rod moving with velocity v parallel to a long straight wire carrying a current i. Calculate the induced emf in the rod.
Submitted By Mr. Ajay Sharma
Email Id : [email protected]
