A proton beam is going from north to south and an electron beam is going from south to north. Neglecting the earth's magnetic field, the electron beam will be deflected:

Consider the situation shown in the figure. The straight wire is fixed but the loop can move under magnetic force. The loop will 

1.  remain stationary

2.  move towards the wire

3.  move away from the wire

4.  rotate about the wire

Two parallel wires carry currents of 20 A and 40 A in opposite directions. Another wire carrying a current antiparallel to 20 A is placed midway between the two wires. The magnetic force on it will be

1.   towards 20 A

2.   towards 40 A

3.   zero

4.   perpendicular to the plane of the currents

Two parallel, long wires carry currents i₁, and i₂ with i₁ > i₂. When the currents are in the same direction, the magnetic field at a point midway between the wires is 10 µT. If the direction of i₂ is reversed, the field becomes 30 µT. The ratio i₁/i₂ is

1.   4

2.   3

3.   2

4.   1

Consider a long, straight wire of cross-sectional area A carrying a current i. Let there be n free electrons per unit volume. An observer places himself on a trolley moving in the direction opposite to the current with a speed v = \(\frac{\mathrm{i}}{\mathrm{n} \mathrm{Ae}}\)and separated from the wire by a distance r. The magnetic field seen by the observer is very nearly

1.    \(\frac{\mu_{0} i}{2 \pi r}\) 

2.   Zero

3.   \(\frac{\mu_{0} i}{ \pi r}\) 

4.   \(\frac{2\mu_{0} i}{\pi r}\)