Quantum Physics

Question 1

What is the photoelectric effect?

Answer 1

When a metal surface is shone with a light causing electrons to be emitted because the light transfers energy to the electrons, allowing them to escape.

Question 2

Why does light of a lower wavelength (e.g. red) not trigger the photoelectric effect.

Answer 2

The energy is not high enough to cause the electron to leave it’s ‘pit’

Question 3

How does a gold leaf electroscope work?

Answer 3

A gold leaf electroscope is negatively charged causing the stem and leaf to repel each other.
If ultraviolet light is shone onto the metal plate, electrons begin to escape so charge is lost.
Therefore, the gold leaf will drop as it’s no longer being repelled.

Question 4

Why does the gold leaf electroscope show that light is a particle?

Answer 4

There is a threshold frequency because electrons are not emitted if the light is below a certain frequency. This doesn’t make sense in a wave model because if the energy wasn’t enough, more energy would come and it would be raised partly.

Question 5

What is the minimum energy to free an electron known as?

Answer 5

The work function: Φ

Question 6

How do you calculate the energy of a photon?

Answer 6

E = hf
E = Energy
H = Planck's Constant (6.63x10⁻³⁴Js⁻¹)
f = frequency

Question 7

What does excess energy gained from light become in a photoelectron?

Answer 7

Excess energy that is no longer needed for the work function is spent as kinetic energy.

Question 8

How do you calculate the energy of a photoelectron with the work function?

Answer 8

hf = Φ + Eₖ
Eₖ = Kinetic Energy
Φ = Work Function
hf = Energy
h = Planck's Constant (6.63x10⁻³⁴Js⁻¹)
f = frequency

Question 9

What is the threshold frequency?

Answer 9

h₀ = Φ/h

Question 10

How do we calculate intensity?

Answer 10

Intensity = Power / Area

Question 11

What law does intensity follow?

Answer 11

An inverse square law

Question 12

How do we calculate the frequency of a particle?

Answer 12

f = c/λ

Question 13

How do we calculate the energy of a particle?

Answer 13

E = hc/λ
E = Energy
h = Planck's Constant (6.63x10⁻³⁴Js⁻¹)
c = speed of light (3x10⁸)
λ = wavelength

Question 14

What happens when an electron gets excited?

Answer 14

The electron moves to a higher energy level in the atom.

Question 15

What is the lowest energy state of an atom called?

Answer 15

The ground state.

Question 16

Why do gases emit light when they’re in low pressure and a current is sent through?

Answer 16

The atom gains energy from the electrons and is excited so it goes above it’s energy level. The electron doesn’t have the energy to maintain this so it falls back to it’s original energy level and emits photons.