Q.21)-Suitable impurities are added to a semiconductor depending on its use. This is done in order to
- increase its life
- enable it to withstand higher voltages
- increase its electrical conductivity
- increase its electrical resistivity
Q.22)-Of the following natural phenomena, tell which one known in Sanskrit as 'deer's thirst'?
- Rainbow
- Earthshine
- Halo
- Mirage
Q.23)-One thousand microns is equal to
- 10-3m
- 10-6m
- 10-9m
- 10-12m
Q.24)-Sound travels at the fastest speed in
- steel
- water
- air
- vacuum
Q.25)-Superconductors are substances which
- conduct electricity at low temperature
- offer high resistance to the flow of current
- offer no resistance to the flow of electricity
- conduct electricity at high temperatures
Q.26)-Light travels at the fastest speed in
- glass
- water
- hydrogen
- vacuum
Q.27)-Optical fibre works on the
- principle of refraction
- total internal reflection
- scattering
- interference
Q.28)-Light from the star, Alpha Centauri, which is nearest to the earth after the sun, reaches the earth in
- 4.2 seconds
- 42 seconds
- 4.2 years
- 42 years
Q.29)-Radio telescopes are better than optical telescopes because
- they can detect faint galaxies which no optical telescope can
- they can work even in cloudy conditions
- they can work during the day and night
- All of the above
Q.30)-Light Emitting Diodes (LED) is used in fancy electronic devices such as toys emit
- X-rays
- ultraviolet light
- visible light
- radio waves