Mechanics and Quantum

The wavelength of light from an LED is 480 nm. The radiant power emitted from the LED is 1.2 mW.

Calculate the number of photons N emitted from the LED per second.

• 2.5x10*7

• 2.9 × 10*15

• 3.1x10*9

• 4.5x10*15

beam of monochromatic light passes from air into glass. The speed of the photons in air is 3.0 x 108 m s−1

and in glass is 2.0 x 108 m s−1.

Which of the following statements is correct?

• The energy of a photon in glass is 1.5 times the energy of the photon in air.

• The energy of a photon in glass is the same as the energy of the photon in air.

• The energy of a photon in glass is of the energy of the photon in air.

• When the intensity of the monochromatic light beam is halved the energy of each photon of the beam in

  air is halved.

Violet light is incident on the surface of a metal. Photoelectrons are emitted from the surface of the metal. The

frequency of the radiation incident on this metal is increased but the intensity of the radiation is kept constant.

Which statement is correct?

• The value of the Planck constant increases.

• The work function of the metal increases.

• The number of photoelectrons emitted per second increases.

• The maximum kinetic energy of photoelectrons increases.

The total energy gained by 20 electrons travelling through a potential difference V is 30 keV. What is the

potential difference V?

• 1.5 V

• 3.0V

• 1500V

• 3000V

A stationary sound wave, of fundamental mode of vibration, is formed in a tube closed at one end.

The length of the tube is 0.17 m. The speed of sound in air is 340 m s−1.

What is the fundamental frequency of the stationary wave?

• 500Hz

• 1000Hz

• 2000Hz

• 4000Hz

A golf ball is dropped from rest onto a hard floor.

The graph shows how the velocity of the ball varies with time as it bounces, from the time of release.

At which point does the ball reach its maximum height after the first bounce?

• A

• B

• C

• D

A suitcase weighing 200 N is placed on a weighing scale in a lift.

The scale reads 180 N when the lift is moving.

• moving down at a constant velocity.

• moving down with a decreasing velocity

• moving up at a constant velocity.

• moving up with a decreasing velocity.

A uniform metre ruler of weight 2.0 N is freely pivoted at the 70 cm mark.

A student holds the ruler in a horizontal position and suspends a 5.0 N weight from the 100 cm

end.

What is the magnitude of the resultant moment when the student releases the ruler?

• O.15Nm

• 0.19Nm

• 1.1Nm

• 1.9Nm