21.

'Parsec' is the unit measurement of

• Density of mars

• Astronomical distance

• Brightness of heavenly bodies

• Brightness of heavenly bodies

Atomic explosion is triggered by

• thermo nuclear reaction

• chemical reaction

• controlled chain reaction

• controlled chain reaction

The phenomenon of change in direction of light when it passes from one medium to another is called

• propagation

• reflection

• refraction

• refraction

Why does a cannon recoil after firing?

• Conservation of energy

• Backward thrust of gases produced

• Newton's third law of motion

• Newton's third law of motion

A bomb explodes on the moon. You will hear its sound on earth after ........

• 20 min

• 2 hours 20 min

• 3.7 hours

• 3.7 hours

Which one of the following takes place during a nuclear fusion?

• A heavy nucleus bombarded by neutrons breaks up

• A heavy nucleus breaks up spontaneously

• Two light nuclei combine to form a heavy nucleus

• Two light nuclei combine to form a heavy nucleus

Which term is not associated with sound waves?

• Hertz

• Decibel

• Candela

• Candela

If an electron and a photon have the same wavelength, then they will have the same

• Velocity

• Linear momentum

• Angular momentum

• Angular momentum

A particle is thrown vertically upward. When it reaches the highest point, it has ..........

• a downward acceleration

• an upward acceleration

• a downward velocity

• a downward velocity

The quality or tone of a musical sound produced by a stringed instrument depends on

• frequency of vibration

• length of the strings in the instrument

• amplitude of vibration

• amplitude of vibration