**Select the correct answer in each of the following options.**

(1) A moving charge is surrounded by

**(a) 2 fields** (b)
3 fields (c) 4
fields (d) none

**Explanation:** A moving charge is surrounded by two
fields; one the electric field due to the charge and the other the magnetic
field due to the motion of charge.

(2) A photon while moving through a magnetic field is deflected towards

(a) North pole (b)
South pole (c) is
ionized **(d)
none **

**Explanation:** A photon has no charge on it and is not affected by any of the poles of the magnetic field or ionized.

(3) Magnetism is related to

(a) Stationary charge **(b)
moving charge** (c)
stationary and moving charge (d)
law of motion

Note that magnetism is the phenomenon associated with moving charges.

(4) When a charge particle enters perpendicular to a magnetic field, the path followed by it is

(a) A helix **(b)
a circle** (c)
straight line (d) ellipse

**Explanation:** The magnetic force acting on the particle is perpendicular to the velocity of the particle and provides the necessary centripetal force to move the particle in a circle.

(5) The torque acting on a coil can be increased by increasing

(a) number of turns (b)
current and magnetic field (c) area
of the coil **(d) all the
above**

**Explanation:**
Τ = NIAB. Therefore, torque can
be increased by increasing the number of turns N, current I, magnetic field B
and area of the coil A. For more details see comprehensive question 2.

(6) The magnetic flux will be maximum for an angle of

**(a) 0°** (b)
60° (c)
90° (d) 180°

**Explanation:** Since magnetic flux = Φ = BA cosθ and
cosθ is maximum for 0^{0} and so do the magnetic flux.

(7) The Weber is a unit of measure of

(a) Conductance (b)
electric current **(c)
magnetic flux** (d)
electric flux

(8) One Weber is equal to

(a) N A^{2}/m (b)
N m^{2}/A (c)
N A/m **(d)
N m/A**

**Explanation:** Since B = F/IL, therefore, unit of magnetic induction B is N/A m = N A-1 m-1. Similarly, magnetic flux ϕ = BA = N A-1 m-1 m2 = N m A-1.

(9) An electron moves at 2 * 10^{2} m/s and enters
perpendicular to the magnetic field of 2 T. What is the magnitude of magnetic force?

(a) 1 * 10^{-6} N **(b)
6.4 * 10 ^{-17} N** (c)
3.6 * 10

^{-24}N (d) 4 * 10

^{6}N

**Solution: ** Force on the electron in a magnetic field is
given by F = e(v x B) = evBsinθ . Put the values,

F = 1.6 * 10^{-19 }(2 * 10^{2} * 2 * 1) =
1.6 * 2 * 2 * 10^{-19+2} = 6.4 * 10^{-17} N.

Here 1.6 * 10^{-19} is charge on the electron and
sin90^{0} = 1.

For details see comprehensive question 3.

(10) The force on a charged particle moving parallel to the magnetic field is

(a) Maximum (b)
minimum **(c)
zero** (d)
none

**Explanation:** In a magnetic field B, the force on a
charged particle q moving with velocity v is

F = q (v x B) = qvBsinθ

Put θ = 0^{0}, then sinθ = 0 (the case when v and B are parallel) and the force will also be zero.

(11) Ampere law is applicable to

(a) Circular path (b)
rectangular path **(c) to any
closed path** (d) none of these

(Do you know the difference between a circular path, a rectangular path and an any closed path?)

(12) The unit of permeability of free space is

**(a)T.m/a** (b)
T.m^{2}/A (c)
T.m/A^{2} (d)
None

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