Physics
Define the term 'Quantum'
- A small discrete unit of energy
Define a 'Photon'
A quantum associated with EM radiation
Give both formulae for Energy of a photon
E = hf or E = hc/λ
E - Energy of a photon
f - frequency of a photon/EM radiation
h - planck's constant
c - speed of light
λ - wavelength
Define 'Work Function'
The minimum energy needed to release an electron from its surface
Give another way of finding the energy of a photon
Work function + (MAX)kinetic energy of the electron
Define 'Threshold frequency'
The minimal frequency of radiation that'll result in the emission of electrons from a certain metal surface. Normal UV
What does the photoelectric effect prove
Proves that light is quantised, it's shown by the e- have a 1 to 1 ratio meaning that only frequencies above the threshold frequency will emit e-'s
What is the photoelectric effect
The process of liberating an electron from its surface
Give 1 thing intensity affects and 1 thing it has no effect on
- It's directly proportional to the no of emitted e-'s
- It doesnt affect the KE of each electron
What is the one thing frequency of the incident ray affects
The KE of the photoelectron
Why do we use KE(max) instead of just KE
As e-s at the top of the surface need the least energy to be emitted
What's the only way to get a meaningful de broglie wavelength
- Using very light(weighted) particles
- e- musn't be too fast
define Accelerating pd
the pd between the cathode and the anode
What happens after e-s are accelerated out of the cathode and anode
- they're accelerated onto a thin graphite film, which diffracts them onto a phosphorus screen which lights up and shows concentric rings
How does accelerating voltage affect rings
Low accelerating voltage = more spread out rings
High accelerating voltage = more compact rings
How does wavelength affect accelerating pd
Greater wavelength = smaller accelerating pd
Smaller wavelength = greater accelerating pd
How does wavelength affect the angle between the maxima
Big wavelength = big angle between maxima
small wavelength = small angle between maxima
Give 2 de broglies wavelengths
λ = h/p=(h/mv)
λ = h/√2m(KE) = h/√2m(eV)
How do electrons show particle like behaviour
Electrons are emitted instantaneously once the photon reaches the metal surface
Give 2 ways e-s demonstrate particle behaviour
- e-s exchange momentum and energy (obey conservation of energy and momentum)
- e-s hit the phosphorus screen with a discrete impact (not continuous like waves)