Photoelectric Effect

Question 1

What is the photoelectric effect?

Answer 1

Electromagnetic radiation shines of metal, metal absorbs some radiated energy

Some electrons may absorb enough energy to liberate them from their orbits.

Observation that UV can cause something to lose charges.

Question 2

What are photons?

Answer 2

The idea that light is made up of individual units called photons

Light travels in small ‘bundles’ and has a certain amount of every associated with it, a ‘quantum’.

Question 3

E = hf

Answer 3

Planck’s formula, showing how much energy in a given quantum

h = Planck’s constant, 6.63x10^-34 Js 
f = frequency of the beam of light 
E = energy of light emitted

Question 4

What is intensity of light a measure of?

Answer 4

How MANY photons there are.

Does NOT depend on colour

Question 5

Monochromatic

Answer 5

Light of a single frequency

Question 6

Photoemission

Answer 6

Occurs when a photon of sufficient energy (a sufficiently high FREQUENCY) strikes a metal and an electron gains enough energy to overcome the weak attractive forces

Must be a reactive metal (weak attraction)

Therefore dim violet light will work but not bright red light

Question 7

What is the work function

Answer 7

Then MINIMUM amount of energy needed to remove the electron

Y-int of a Ek vs f graph

Φ = hf0
f0 is min frequency required (threshold frequency)

Question 8

Equation to find Ek max of an ejected electron

Answer 8

Ek = eV

e is charge on electron

V is stopping voltage (of photoelectric cell)

From W=Vq

Question 9

hf = Φ + Ek

Answer 9

From the graph of Ek vs f
(If written in Y=mx+c form;
Ek = hf - Φ)

hf is the energy of the incident photon
Φ is the work function
Any leftover energy becomes the Ek of the ejected electron

Can be written as hf = Φ + eV

Question 10

How does the intensity of the light affect Electrons emitted?

Answer 10

Greater intensity results in a greater number of electrons that fly off (more protons to knock off more electrons)

BUT does not affect Ek of emitted electrons (speed)

Frequency must be above the threshold frequency - an intense low frequency light will not eject electrons.