41.

If a small amount of antimony is added to germanium crystal

• the antimony becomes an acceptor atom

• there will be more free electrons than holes in the semiconductor

• its resistance is increased

• its resistance is increased

Fusion reaction takes place at high temperature because

• atoms get ionised at high temperature

• kinetic energy is high enough to overcome the coulomb repulsion between nuclei

• molecules break up at high temperature

• molecules break up at high temperature

A nucleus  emits one α - particle and two β^- particles. The resulting nucleus is 

Photoelectric emission occurs only when the incident light has more than a certain minimum

• wavelength

• intensity

• frequency

• frequency

Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de - Broglie wavelength associated with the electrons would

• decrease by 2 times

• decrease by 4 times

• increase by 4 times

• increase by 4 times

A biconvex lens has a radius of curvature of magnitude 20 cm. Which one of the following options describes best the image formed on an object of height 2 cm placed 30 cm from the lens?

• Virtual, upright, height = 0.5 cm

• Real, invented, height = 4 cm

• Real, inverted, height = 1 cm

• Real, inverted, height = 1 cm

The wavelength of the first line of Layman series for the hydrogen atom is equal to that of the second line of Balmer series for a hydrogen-like an ion. The atomic number Z  of hydrogen-like ion is 

• 4

• 1

• 2

• 2

Which of the following is not due to total internal reflection ?

• Difference between apparent and real depth of a pond

• Mirage on hot summer days

• Brilliance of diamond

• Brilliance of diamond

In forward biasing of the p - n junction

• the positive terminal of the battery is connected to n - side and the depletion region becomes thin

• the positive terminal of the battery is connected to n- side and the depletion region becomes thick

• the positive terminal of the battery is connected to p - side and the depletion region become thin

• the positive terminal of the battery is connected to p - side and the depletion region become thin

A transistor is operated in common emitter configuration V_C = 2V such that change n the base current from 100 µA to 300 µA produces a change in the collector current from 10 mA to 20 mA. The current gain is

• 75

• 100

• 25

• 25