A radiation P is focused by a proper device on the bulb of a thermometer. Mercury in the thermometer shows a rapid increase. The radiation P is —

1. infrared radiation
2. visible light
3. ultraviolet radiation
4. X-rays

For obtaining the spectrum of infrared radiation, the material of prism should be :

1. glass
2. quartz
3. rock salt
4. does not matter

The waves used for taking photographs at night are :

1. infrared waves
2. microwaves
3. radio waves
4. ultrasonic waves

The radiation used for satellite communication is :

1. microwaves
2. radio waves
3. gamma rays
4. X-rays