A short magnet is allowed to fall along the axis of a horizontal metallic ring. Starting from rest, the distance fallen by the magnet in one second may be:
1. 4 m
2. 5 m
3. 6 m
4. 7 m
The magnetic flux linked with a coil varies with time as \(\phi = 2t^2-6t+5,\) where \(\phi \) is in Weber and \(t\) is in seconds. The induced current is zero at:
1. \(t=0\)
2. \(t= 1.5~\text{s}\)
3. \(t=3~\text{s}\)
4. \(t=5~\text{s}\)
The net magnetic flux through any closed surface, kept in uniform magnetic field is:
1. Zero
2.
3.
4.
If a current is passed through a circular loop of radius R then magnetic flux through a coplanar square loop of side l as shown in the figure (l<<R) is:
1.
2.
3.
4.
The radius of a loop as shown in the figure is \(10~\mathrm {cm}.\) If the magnetic field is uniform and has a value \(10^{-2}~ T,\) then the flux through the loop will be:
1. | \(2 \pi \times 10^{-2}Wb\) | 2. | \(3 \pi \times 10^{-4}Wb\) |
3. | \(5 \pi \times 10^{-5}Wb\) | 4. | \(5 \pi \times 10^{-4}Wb\) |
Eddy currents are used in:
1. Induction furnace
2. Electromagnetic brakes
3. Speedometers
4. All of these
The current through a choke coil increases from zero to 6 A in 0.3 seconds and an induced emf of 30 V is produced. The inductance of the coil is:
1. | 5 H | 2. | 2.5 H |
3. | 1.5 H | 4. | 2 H |
Two coils have a mutual inductance of 5 mH. The current changes in the first coil according to the equation \(I=I_{0}cos\omega t,\) where \(I_{0}=10~A\) and = 100 rad/s. The maximum value of e.m.f. induced in the second coil is:
1. 5 Volt
2. 2 Volt
3. 4 Volt
4. Volt
A small square loop of wire of side 'l' is placed inside a large square loop of side 'L' (Ll). If the loops are coplanar and their centres coincide, the mutual inductance of the system is directly proportional to:
1. L/l
2. l/L
3. L2/l
4. l2/L