151. Self-inductance of a long solenoid is______________?
A. μoN2A
B. μoN2/A
C. μoN2
D. BA
152. A coil of wire is arranged with its plane perpendicular to a uniform magnetic field o flux density B. when the radius of the coil increases from r1 to r2 in time Δt then what is the emf induced in the coil ?
A. ωB/r22-r12/Δt
B. ωB(r2-r1)2/Δt
C. ωB(r22-r12)/Δt
D. ωB(r22+r12)/Δt
153. When we rub a glass rod with a silk cloth then________________?
A. glass rod acquires negative charge while silk acquires positive charge
B. glass rod acquires positive charge while silk acquires negative charges
C. both glass rod and silk acquire negative charge
D. both glass rod and silk acquire positive charge
154. The minimum charge on any object cannot be less than_______________?
A. 1.6 x 10-19C
B. 3.2 x 10-19C
C. 9.1 x 109C
D. no definite value exist
155. Electric force between two point charges in air or vacuum is F. If we replace air or vacuum by an insulator (dielectric) of relative permitivity Cr the force between the charges will_______________?
A. decrease
B. increase
C. remain constant
D. depends upon composition of dielectric
156. Transformer works on the principle of________________?
A. Lenzs law
B. Faradays law
C. Mutual induction
D. Law of conservation of power
157. When the motor is at its maximum speed then back emf will be______________?
A. Maximum
B. Zero
C. Intermediate values
D. No back emf
158. Lagging of changes in the magnetization of a substance behind changes in the magnetic field as the magnetic field is varied is known as magnetic_____________?
A. Retaintivity
B. Permeability
C. Flux
D. Hysteresis
159. For long distance transmission the transformer used is_____________?
A. Step down
B. Input voltage and output voltage remain same
C. Step up
D. Amplifier is used
160. Which one of the following devices does not function like an electric motor ?
A. Galvanometer
B. Ammeter
C. Voltmeter
D. Transformer
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