12 Physics Test Paper CH 4 1
12 Physics Test Paper CH 4 1
12 Physics Test Paper CH 4 1
Test Paper-01
Class - 12 Physics (Moving Charges and Magnetism)
1. The magnetic field at the centre of the circular coil of radius 1 cm and carrying
current of 4 A is
a.
b.
c.
d.
a. IAd
b. μIA
c. IA/d
d. IA
a.
b.
c.
d.
a. 100
b. 250
c. 300
d. 150
5. A wire of length L carrying current i is placed perpendicular to the magnetic
induction B. The total force on the wire is
a. LB/i
b. iL/B
c. iLB
d. iB/L
7. Under what conditions is the force acting on a charge moving through a uniform
magnetic field minimum?
8. 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?
10. Two long parallel straight wires X and Y separated by a distance of 5 cm in air carry
currents of 10 A and 5 A respectively in opposite directions. Calculate the magnitude
and direction of the force on a 20 cm length of the wire Y.
11. An electron is moving along +ve x-axis in the presence of uniform magnetic field
along +ve y-axis. What is the direction of force acting on it?
12. Two parallel coaxial circular coils of equal radius 'R' and equal number of turns 'N',
carry equal currents 'I' in the same direction and are separated by a distance '2R'.
Find the magnitude and direction of the net magnetic field produced at the midpoint
of the line joining their centres.
13. An electron traveling west to east enters a chamber having a uniform electrostatic
field in north to south direction. Specify the direction in which a uniform magnetic
14. Define current sensitivity and voltage sensitivity of a galvanometer. Increasing the
current sensitivity may not necessarily increase the voltage sensitivity of
galvanometer. Justify
15. If a piece of metal has a charge and is placed inside a hollow metal sphere of
radius 20 cm (without touching it), what is the potential of the sphere? What will the
potential of the sphere become, if
1. c.
2. d. IA
Explanation: The torque experienced by a current carrying coil of N turns
placed in a magnetic field .
For N =1, Comparing with torque experienced by a electric dipole
we get hence .
3. d.
Explanation: The expression for Ampere’s circuital law is
Where I is the current included in the surface bounded by the line integral.
4. d. 150
Explanation:
5. c. iLB
Explanation: Magnitude of the Force experienced by a current carrying
conductor placed in a magnetic field is . If the angle between the
directions of the current and the magnetic field is 90⁰, F= iLB
7. When a charge moves parallel or antiparallel to the direction of the magnetic field,
the force acting on it is zero or minimum.
The direction of force is perpendicular to the length of wire Y and acts away from X.
or
13. The electrostatic field is directed towards south. Since the electron is a negatively
charged particle, therefore, the electrostatic field shall exert a force directed towards
north. So, if the electron is to be prevented from deflection from straight path, by the
magnetic force on the electron should be directed towards south. Now
hand rule we find that magnetic field should be in the vertically downward
direction.
14. The definition of current sensitivity and voltage sensitivity are given
Let the deflection produced in applying voltage V is then
Voltage sensitivity
15. On the inner and outer sphere's surface charges of and are
induced respectively. The potential of the sphere relative to earth is determined solely
by the outer surface charge q.
a. The potential of the sphere is momentarily reduced to zero when it is earthed. The
positive charge on the outer surface disappears but the induced negative charge
inside remains. Therefore, the potential of the sphere is zero.
b. The induced negative charge is neutralized when the metal touches the sphere
and no charge remains on the metal or sphere. Both are at the same potential i.e.
zero potential.