# Test – Important Numericals – Chapter 4 – Moving Charges & Magnetism – Class 12 Physics

## Test - Chapter 4 - Moving Charges & Magnetism - Numericals.

1. A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?

2. An electron of kinetic energy 25KeV moves perpendicular to the direction of a uniform magnetic field of 0.2 millitesla. Calculate the time period of rotation of the electron in the magnetic field.

3. A closely wound solenoid of 2000 turns and cross sectional area 1.6 × 10-4 m2carrying a current of 4.0 A is suspended through its centre allowing it to turn in a horizontal plane. Find

(i) the magnetic moment associated with the solenoid,

(ii) magnitude and direction of the torque on the solenoid if a horizontal magnetic field of 7.5 × 10-2 T is set up at an angle of 30° with the axis of the solenoid.  (Comptt. All India 2014)

4. A long straight wire in the horizontal plane carries a current of 50 A in the north to south direction. Give the magnitude and direction of B at a point 2.5 m east of the wire.

5. An ammeter of resistance 0.80 Ω can measure current upto 1.0 A.

(i) What must be the value of shunt resistance to enable the ammeter to measure current upto 5.0A?

(ii) What is the combined resistance of the ammeter and the shunt? (Delhi 2013)

6. It is desired to pass only 10% of the current through a galvanometer of resistance 90 ohm. How much shunt resistance be connected across the galvanometer?

7. An electron moves around the nucleus in a hydrogen atom of radius 0.51 A, with a velocity of 2 × 105m/s. Calculate the following :

(i) the equivalent current due to orbital motion of electron

(ii) the magnetic field produced at the centre of the nucleus

(iii) the magnetic moment associated with the electron. (All India 2015)

8. What is the magnitude of magnetic force per unit length on a wire carrying a current of 8A and making an angle of 30º with the direction of a uniform magnetic field of 0.15 T?

9. Two identical coils, each of radius ‘R’ and number of turns ‘N’ are lying in perpendicular planes such that their centers coincide. Find the magnitude and direction of the resultant magnetic field at the center of the coils, if they are carrying currents ‘I’ and √2I respectively. (Comptt. Delhi 2010)

10. A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?

11. A particle of mass 2 x 10-3kg and charge 2 µC enters into a uniform electric field of 5 × 105 NC-1, moving with a velocity of 10 ms-1 in a direction opposite to that of the field. Calculate the distance it would travel before coming to rest. (Comptt. Delhi 2011)

12. A square loop of side 20 cm carrying current of 1A is kept near an infinite long straight wire carrying a current of 2A in the same plane as shown in the figure.

Calculate the magnitude and direction of the net force exerted on the loop due to the current carrying conductor. (Comptt. All India)

13. A circular coil of 200 turns and radius 10 cm is placed in a uniform magnetic field of 0.5 T, normal to the plane of the coil. If the current in the coil is 3.0 A, calculate the

(a) total torque on the coil.

(b) total force on the coil.

(c) average force on each electron in the coil, due to the magnetic field.
Assume the area of cross-section of the wire to be 10-5 m2 and the free electron density is 1029/m3. (All India 2015)

14. Two identical loops P and Q each of radius 5 cm are lying in perpendicular planes such that they have a common centre as shown in the figure. Find the magnitude and direction of the net magnetic field at the common centre of the two coils, if they carry currents equal to 3 A and 4 A respectively. (All India 2017)

15. A circular coil, having 100 turns of wire, of radius (nearly) 20 cm each, lies in the XY plane with its centre at the origin of co-ordinates. Find the magnetic field, at the point (0, 0, 20√3 cm), when this coil carries a current of (Comptt. Delhi 2016)

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