Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Two parallel wires carry currents of 20A and 40A in opposite directions. Another wire carying a current anti parallel to 20A is placed midway between the two wires. T he magnetic force on it will be:

1. Towards 20A.
2. Towards 40A.
3. Zero.
4. Perpendicular to the plane of the currents.

The magnetic force required to demagnetise the material is:

A 50 turns circular coil has a radius of 3 cm, it is kept in a magnetic field acting normal to the area of the coil. The magnetic field B  increased from 0.10 tesla to 0.35 tesla in 2 milliseconds. The average induced e.m.f. in the coil is

(a) 1.77 volts

(b) 17.7 volts

(c) 177 volts

(d) 0.177 volts

Suppose, the electron in a hydrogen atom makes transition from n = 3 to n = 2 in 10^-8s. The order of the torque acting on the electron in this period, using the relation between torque and angular momentum as discussed in the chapter on rotational mechanics is:

1. 10^-34Nm
2. 10^-24Nm
3. 10^-42Nm
4. 10^-8Nm

On increasing the temperature of a conductor, its resistance increases because

(a) Relaxation time decreases	(b) Mass of the electrons increases
(c) Electron density decreases	(d) None of the above

The magnetic moment of a magnet of length 10 cm and pole strength 4.0 Am will be

(a)

(b) 1.6

(c) 20

(d) 8.0

If the potential at each point on a conductor is same to each other, then:

A new flashlight cell of e.m.f. 1.5 volts gives a current of 15 amps, when connected directly to an ammeter of resistance 0.04Ω. The internal resistance of cell is

(a) 0.04 Ω

(b) 0.06 Ω

(c) 0.10 Ω

(d) 10 Ω

A student has 10 resistors of resistance ‘r’. The minimum resistance made by him from given resistors is

(a) 10 r

(b)

(c)

(d)