Current Electricity — Physics STD 12 Science — Question

In an electric motor, wires carrying a current of 5A are placed at right angles to a magnetic field of induction 0.8T. If each wire has length of 20cm, then the force acting on each wire is:

The cut-in voltage for silicon diode is approximately

(a) 0.2 V

(b) 0.6 V

(c) 1.1 V

(d) 1.4 V

The forbidden energy gap for germanium crystal at 0 K is:

If an observer is moving with respect to a stationary electron, then he observes

(a) Only magnetic field

(b) Only electric field

(c) Both (a) and (b)

(d) None of the above

An electron passing through a potential difference of 4.9 V collides with a mercury atom and transfers it to the first excited state. What is the wavelength of a photon corresponding to the transition of the mercury atom to its normal state

(a) 2050 Å

(b) 2240 Å

(c) 2525 Å

(d) 2935 Å

An object 5 cm tall is placed 1m from a concave spherical mirror which has a radius of curvature of 20 cm The size of the image is

(a) 0.11 cm

(b) 0.50 cm

(c) 0.55 cm

(d) 0.60 cm

As the mass number A increases, which of the following quantities related to a nucleus do not change?

1. Mass.
2. Volume.
3. Density.
4. Binding energy.

The capacitive reactance in an AC circuit is.

If the distance between parallel plates of a capacitor is halved and dielectric constant is doubled then the capacitance

(a) Decreases two times	(b) Increases two times
(c) Increases four times	(d) Remain the same