21.

Conduction of thermal energy takes place in

• solids

• liquids

• gases

• All of these

Following is not a property of radiation

• It travels with velocity of light

• Medium is necessary for propagation

• Its nature is electromagnetic

• It has quantum nature

Which of the following characteristics of sound depend on the amplitude of vibrations?

• Speed

• Pitch

• Loudness

• Quality

The amount of matter in same weight will be

• least at North pole

• least at equator

• least at Moon

• same at all of the above places

Select the group of poor conductors of heat from the following.'

• Air, water, plastic

• Wool, wood, iron

• Water, copper, wood

• Air, aluminium, wool

Select the one which is different from the others in the manner it is applied.

• Electrostatic force

• Frictional force

• Gravitational force

• Magnetic force

While teaching the topic on 'Motion and Time' to Class VII students, Savita gave examples of different kinds of motion to the students. Which one of the following examples was quoted by her incorrectly?

• Motion of a boy sitting in a moving car in relation to the car

• Motion of a boy sitting in a merry-go-round

• Motion of the hammer of an electric bell

• Motion of a cricket ball hit by a batsman

Which one of the following is not an example of electromagnetic waves?

• Ultraviolet rays

• Radio waves

• X-rays

• Sound waves in air

Radiation with maximum penetration power is

• infrared radiation

• ultraviolet radiation

• X-rays

• $\mathrm{\gamma }$-rays

The mass of man is 72 kg at Earth. The value of g at the Moon's surface is 1/6 of that on the Earth. The mass of man at the Moon will be

• 12 kg

• 120 kg

• 72 kg

• 432 kg