Quantum (M4)

Question 1

Threshold p.d. / threshold voltage

Answer 1

The minimum potential difference at which a diode begins to conduct.

Question 2

Threshold frequency

Answer 2

The minimum frequency of the electromagnetic radiation that will cause the emission of an electron from the surface of a particular metal.
Symbol: f0
Unit: Hz

Question 3

Photon

Answer 3

A quantum of electromagnetic energy. Photon energy E is given by E=hf where h is the Planck constant and f is the frequency of the EM radiation.

Question 4

Planck’s constant

Answer 4

An important constant in quantum mechanics.
Symbol: h
Value: 6.63x10^-34

Question 5

Electronvolt

Answer 5

A derived unit of energy used for subatomic particles and photons.
Defined as the energy transferred to of from an electron when it passes through a potential difference of 1V.
1eV = 1.6x10^-19 J

Question 6

Wave-particle duality

Answer 6

A theory that states that matter has both particle and wave properties and also electromagnetic waves have both wave and particulate (photon) nature.

Question 7

The De Broglie equation

Answer 7

L = h/p = h/mv
L = wavelength
h = Planck’s constant
p = momentum
m = mass
v = velocity

Question 8

Finding the wavelength of an electron

Answer 8

Work done by the field = eV
Kinetic energy gained by electron = 0.5mvv = pp/2m
eV = pp/2m
From De Broglie theorem: p=h/L
eV = hh/2mLL
L = h/Rt(2meV)
1.67x10^-10 (X-ray wavelength)

Question 9

Photoelectric effect

Answer 9

The emission of photoelectron from a metal surface when EM radiation above a threshold frequency is incident on the metal.

Question 10

Photoelectrons

Answer 10

Electrons emitted from the surface of a metal by the photoelectric effect.

Question 11

Work function

Answer 11

The minimum energy needed to remove a single electron from the surface of a particular metal
Symbol: phi
Unit: J

Question 12

Intensity of a particle

Answer 12

1 photon: E=hf
I = P/A

n photons: E=nhf
P = E/t = nhf/t
I = nhf/At

Question 13

The electron gun

Answer 13

1) Cathode heats up, produces electrons and repels them due to thermionic emission
2) p.d. of 1000s of Volts between anode and cathode. Electrons are repelled from cathode and attracted to anode. Electric field causes resultant force therefore acceleration. Electrons go through hole in anode, producing the electron beam
3) W = Qv = eV
Due to law of conservation of energy eV = 0.5mvv
e, V and m are known so can calculate v