2.7 Photons

Question 1

What is the formula for energy of a photon?

Answer 1

E = hf
(Energy = Planks constant x frequency)

Question 2

What is 1 eV (Electron volt)

Answer 2

The energy gained by an electron through a p.d. of 1V between them
1ev - 1.6 x 10^-19

Question 3

How do you find plank’s constant?

Answer 3

1) Create a circuit with a variable cell, resistor and an LED with a voltmeter in parallel with it. (The LED should have a known wavelength/ λ)
2) Increase the voltage until light is just being emitted from the LED by using a dark tube and record the voltmeter reading at this point
3) Repeat step 2 for LEDs with different wavelengths
4) Plot a graph with the minimum voltage (y-axis) against 1/λ
5) Find the gradient of the graph and use the equation eV = hc/λ and rearrange to make Vλ = hc/e where Vλ is the gradient.
6) Finally Vλe/c will give h, plank’s constant.

Question 4

What is the equation for the photo electric effect?

Answer 4

E max = hf - Φ

Question 5

What is the photo electric effect?

Answer 5

When photons of a certain wavelength interact with a metal surface, it can give the electrons in the metal enough energy to escape the charge of the atoms and be emitted from the surface

Question 6

What is ionisation?

Answer 6

The removal of one or more electrons from an atom

Question 7

How does electron diffraction work?

Answer 7

When electrons are pasted through graphite, the small gaps in it act as slits which cause the electrons to diffract and interfere with one another which causes an interference pattern

Question 8

What is de Broglie’s equation?