4.5: Quantum Physics, F

Question 1

Define: Quantum (plural quanta)

Answer 1

A small discrete unit of energy

Question 2

What is a photon?

Answer 2

A quantum associated with EM radiation

Question 3

What is a threshold voltage?

Answer 3

The minimum voltage required for a current to flow through

Question 4

What is the photoelectric effect?

Answer 4

When 1 photon of light hits a material it emits 1 electron

Question 5

What is the name of the type of electrons released from the photoelectric effect?

Answer 5

Photoelectrons

Question 6

Fill in the blank about the photoelectric effect:

The number of photoelectrons emitted per second is ____________ to the _________ of the radiation.

Answer 6

The number of photoelectrons emitted per second is ‘proportional’ to the ‘intensity’ of the radiation.

Question 7

The maximum kinetic energy of a photoelectron is affected by what factor?

Answer 7

Frequency of the radiation

Question 8

The maximum kinetic energy of a photoelectron is not affected by what factor?

Answer 8

Intensity of the radiation

Question 9

Explain briefly 2 reasons why the photoelectric effect couldn’t be explained by wave theory?

Answer 9

Any 2:

• Kinetic energy should increase with intensity(didn’t)
• No explanation for kinetic energy depending only on free
• No explanation for threshold freq

Question 10

What 2 reasons meant the photon model explained the photoelectric well?

Answer 10

• If a ‘these’ photons are absorbed by a free electron, the electron will gain energy equal to ‘hf’
• Metal is bombarded by photons when exposed to light

Question 11

Define: work function

Answer 11

Minimum energy required to release 1 electron from its surface

Question 12

How does the photon model explain threshold frequency

Answer 12

If the energy gained by a photon is greater than the work function, it will be emitted

Question 13

What is the minimum amount of energy a work function can lose?

Answer 13

Energy equal to the work function

Question 14

Rate of photon emission is ________ proportional to _________ provided it is above the threshold _________
Fill in the blank

Answer 14

Rate of photon emission is ‘directly’ proportional to ‘intensity’ provided it is above the threshold ‘frequency’

Question 15

Define: Threshold frequency

Answer 15

Lowest frequency required for electrons to be emitted from a metal surface

Question 16

What experiments can be conducted to display light acting as a wave?

Answer 16

Interference and diffraction

Question 17

Define: Electronvolt

Answer 17

Kinetic energy gained by an electron when accelerated through a voltage of 1V

Question 18

What experiment can be conducted to display light behaving as a particle

Answer 18

Photoelectric effect

Question 19

When does electron diffraction occur?

Answer 19

If a particle interacts with an object roughly the same size as its de Broglie wavelength