Photoelectric Effect (3.5)

Question 1

What is the Photoelectric Effect

Answer 1

It is the emission of electrons from a metal surface when it is irradiated with light

Question 2

Expectation vs Observation

Answer 2

Expectation:

• Bright light would cause electrons with greater energy to be released
• In very dim light, it would take some time before any electrons received enough energy to escape the metal
• The frequency (colour) would not affect the energy of the emitted electrons

Observation:

• Brighter light caused more electrons to be emitted ‘per second’ but had the the ‘same energy’
• Even in the faintest light, electrons are emitted instantly
• High frequencies resulted in higher energy (kinetic energy) while below a certain frequency resulted in no electrons emitted.

Question 3

Duality of Light

Answer 3

Light does not behave exactly a wave or a particle, but instead as ‘both’ a wave and a particle (packets of energy called photons)

Question 4

Energy of Photon

Answer 4

Each photon has a fixed amount of energy and is only dependent on the frequency of the light

Question 5

Work Function

Answer 5

Amount of energy required to emit an electron from that of a ‘specific’ metal

Question 6

Threshold Frequency

Answer 6

Minimum frequency below which photoelectric emission is not possible, irrespective of the intensity.

Question 7

Process of Photoelectric Emission

Answer 7

1) If the energy of the photon is less than that of the work function, there will be no emission of electrons from the metal (since the attractive forces between the nuclei and the electrons cannot be overcome)

2) If the frequency/energy of the photon is equivalent to that of the work function, the electron will be emitted (reach the surface), but they possess no kinetic energy/equal to zero

3) If the frequency/energy of the photon is greater than that of the work function, the electron will be emitted with excess kinetic energy as it will move away from the metal