Chapter 13 Quantum Physics

Question 1

What are photons?

Answer 1

Photons are tiny packets of energy. Which show both particle and wave behaviour.

Question 2

How is the energy of a photon related to its frequency?

Answer 2

They are directly proportional

E=hf

Question 3

How do you derive the equation including E,h,c and lambda?

Answer 3

Use the wave equation v = f x lambda and substitute in the frequency into E = hf.

Question 4

What is Planck’s constant?

Answer 4

6.63x10^-34

Question 5

How do you calculate the energy in one eV?

Answer 5

energy transferred from an electron when it moves through a potential difference of 1V.

Question 6

What is the charge of an electron?

Answer 6

-1.6 x 10^-19

Question 7

Why don’t electrons get freed from a metal when visible light is shone on it?

Answer 7

The frequency is too low and hence the wavelength is too high.

Question 8

What is the proportion of photons to photoelectrons?

Answer 8

1:1

Question 9

why doesn’t increasing the intensity of light start to release photo electrons if more are hitting the surface of the metal per second?

Answer 9

The photons only have a 1:1 ratio and so multiple photons cannot release one electron.

Question 10

What is the name for the minimum amount of energy needed to free an electron from the surface of a metal?

Answer 10

The work function.

Question 11

What is the kinetic energy of a photoelectron if it has only just overcame the work function?

Answer 11

0

Question 12

Why are some of the electrons not emitted from a metal at the moment the energy of the work function is met?

Answer 12

Lots of the electrons are nearer to the nucleus and will require more energy to overcome the forces it has with the nucleus,

Question 13

How can you get electrons to diffract?

Answer 13

Pass them through a material with gaps which are similar to its wavelength such as polycrystalline graphite.

Question 14

What equation links wavelength, momentum and Planck’s constant?

Answer 14

lambda= h/mv

Question 15

Why is the interference pattern of electrons diffracting made of rings?

Answer 15

The waves are diffracted through the graphite which has layers oriented in different directions and so forms the rings.

Question 16

What change happens to the maximum kinetic energy of an emitted electron if the intensity of the light is increased?

Answer 16

No change as each photon has the same energy there are just less of them and they interact in a 1:1 ratio.

Question 17

Define threshold frequency?

Answer 17

The minimum frequency required to free an electron from the surface of a metal;.

Question 18

What happens to the gradient of an energy frequency graph if the threshold frequency is increased?

Answer 18

The gradient would stay the same which is Planck’s constant.

Question 19

Explain what is meant by the de Broglie wavelength of an electron?

Answer 19

Electrons are observed to behave like waves where the electron wavelength depends on its momentum.