12th physics chapter 4 objective questions in English

1. The current sensibility of a moving coil galvanometer increases with decrease in:

(A) magnetic field (B) area of a coil (C) number of turns (D) None of these

2. Which of the following shows that the earth behaves as a magnet?

(A) Repulsion between like poles . (B) Attraction between unlike poles (C) Null points in the magnetic field of a bar magnet (D) No existence of isolated magnetic pole

3. The permeability of a paramagnetic substance is :

(A) very large (B) small but more than unity (C) less than unity (D) negative

4. The sensitivity of a tangent galvanometer can be increased by increasing :

(A) the radius of the coil (B) the external magnetic field (C) the number of turns of the coil (D) all the above

5. A current carrying coil is placed in a uniform magnetic field. If the coil turns through an angle θ, then the torque is directly proportional to :

(A) sin θ (B) cos θ (C) cot θ (D) tan θ

6. When we double the radius of a coil keeping the current through it unchanged, what happens to the magnetic field directed along its axis at far off points ?

(A) halved (B) doubled (C) quadrupled (D) remains unchanged

7. What happens to the magnetic field at the centre of a circular current carrying coil if we double the radius of the coil keeping the current unchanged ?

(A) halved (B) doubled (C) quadrupled (D) remains unchanged

8. Circular loop of radius 0.0157 m carries a current 2 A. The magnetic field at the centre of the loop is :

(A) 1.57 × 10^-3Wb/m² (B) 8.0 × 10^-5 Wb/m² (C) 2.0 × 10^-3 Wb/m² (D) 3.14 × 10^-1 Wb/m²

9. A charged particle of mass m and charge q travels on a circular path of radius r i.e., perpendicular to the magnetic field B. The time taken by particle to complete on revolution is :

(A) 2πq^B/m (B) 2πm/q^B (C) 2πmq/B (D) 2πq²B/m

10. What is the angle of dip at the magnetic poles ?

(A) 30° (B) 0° (C) 45° (D) None of these

11. A wire of length 2 metre carries a current 1 ampere, is bent to form a circle. The magnetic moment of the coil is :

(A) 2π (B) π/2 (C) π/4 (D) 1/π

12. An electron having mass ‘m’ and Kinetic energy E enters in uniform magnetic field B perpendicular, then its frequency will be :

(A) eE/qmB (B) 2πm/eB (C) eB/2πm (D) 2m/eBE

13. A charge + q is sent through a magnetic field. The force acting on it is maximum w hen the angle between the direction of motion of the charged particle and the magnetic field :

(A) 0° (B) 45° (C) 90° (D) 180°

14. The magnetic field produced by straight current (I) carrying conductor at any point on itself is :

(A) zero (B) infinite (C) μ₀I/4πI (D) μ₀I/2πI