1. A charged particle with charge $ q $ moves with velocity $\vec{v}$ in a magnetic field $\vec{B}$. What is the magnetic force experienced by the particle if $\vec{v}$ is parallel to $\vec{B}$?
Solution
Correct: A
When the velocity and magnetic field vectors are parallel, the cross product $\vec{v} imes \vec{B}$ becomes zero, resulting in zero magnetic force ($ \vec{F} = q(\vec{v} imes \vec{B}) $).
2. A current-carrying loop is placed in a uniform magnetic field such that its plane is perpendicular to the field. What is the torque acting on the loop?
Solution
Correct: A
Torque is maximum when the loop is parallel to the field and zero when perpendicular. Since the loop's plane is perpendicular, the angle between $\vec{mu}$ and $\vec{B}$ is 0° ($ au = mu B sin heta $), resulting in zero torque.
3. Two long parallel conductors carry currents $ I_1 $ and $ I_2 $ in opposite directions. If they are separated by distance $ d $, what is the force per unit length between them?
Solution
Correct: A
Parallel currents in opposite directions repel each other. The force per unit length is given by $ F/L = rac{mu_0 I_1 I_2}{2pi d} $.
4. A coil of 100 turns with area $ 0.1 , ext{m}^2 $ rotates at 60 Hz in a magnetic field of 0.3 T. What is the maximum EMF generated?
Solution
Correct: B
Maximum EMF is $ epsilon_0 = N B A omega = 100 imes 0.3 imes 0.1 imes (2pi imes 60) = 1130 $ V.
5. A bar magnet is cut into two equal halves along its axis. Which statement is true?
Solution
Correct: B
Cutting a magnet along the axis results in two smaller bar magnets. Each retains magnetic poles, but the magnetic moment is halved due to reduced length.
6. In which direction does an electron moving east deflect if a magnetic field is directed upward?
Solution
Correct: B
Using the right-hand rule (adjusted for electron's negative charge), the force direction is south ($ vec{F} = -e(vec{v} imes vec{B}) $).
7. A circular coil of radius $ R $ carries current $ I $. What is the magnetic field at the center?
Solution
Correct: A
The formula for a circular loop's magnetic field at the center is $ B = rac{mu_0 I}{2R} $.