Chapter 13

Question 1

What are black bodies?

Answer 1

Perfect absorbers of radiation

Question 2

What is a photon?

Answer 2

A discrete packet of em radiation

Energy of atoms are multiples of Planck constant

Question 3

What is the relationship between energy and frequency?

Answer 3

E=hf
E=hc/lamda

Energy is inversely proportional to wavelength

Also e=vq

Question 4

What is the equation for power of a laser beam

Answer 4

Power= hf/t

Question 5

What is the electron volt?

Answer 5

The work done by an electron of charge 1.6x10^-19 when accelerating between a pd of 1v

Ev=energy/1.6x10^-19

Question 6

What is the golden leaf electroscope experiment

Answer 6

Touch the top plate with a negative electrode to charge the plate. The charge spreads to the stem and golden leaf, they are both negative so they repel

If you put a metal on the plate and shine uv light on it, the leaf falls back to the stem, proving that the stem has emitted electrons and lost its charge

Question 7

What is the photoelectric effect

Answer 7

The emission of photoelectrons from the surface of a metal when it is illuminated by em radiation above the threshold frequency

Question 8

What are the key observations of the photoelectric effect?

Answer 8

Frequency of radiation has to be above the threshold frequency for photoelectrons to be emitted
The emission is instantaneous
Increasing intensity only increases the number of photoelectrons emitted, not their energy as each electron only absorbs 1 photon
The value of kinetic energy increases with frequency, not intensity

Question 9

Why does the photoelectric effect disobey wave theory?

Answer 9

Wave theory says that for any frequency of light, energy is proportional to the intensity of the beam
So electrons should gain energy from em waves gradually which it doesn’t do.

Question 10

What if the frequency of a photon is below the threshold frequency?

Answer 10

Electron goes to a higher energy level but falls back down

Question 11

What is the photon model?

Answer 11

A single electron on the surface of a metal absorbs the energy carried by a single photon

Question 12

What is the work function?

Answer 12

The minimum amount of energy needed by an electron to escape a metals surface

ONLY FROM THE SURFACE

Question 13

What happens to energy in excess of the work function?

Answer 13

It’s becomes the electrons kinetic energy

Hf= work function + ke max

Question 14

What is threshold frequency?

Answer 14

The minimum frequency of em radiation that causes the emission of a photoelectron from the surface of a metal

Work function/h =f

Question 15

What is KEmax?

Answer 15

The maximum kinetic energy of the emitted electron after the work function has been overcome

Question 16

What does increasing intensity do?

Answer 16

It means more photons hit an area per unit time.
Which increases the number of interactions per second
So the number of photoelectrons emitted per second increases

It doesn’t effect the energy of anything

Question 17

Why does the amount of energy required for an electron to emit change?

Answer 17

Work function is just for surface electrons. The deeper you go, the more attraction there is so more energy is required to free them.
The deeper you go, the less KEmax they have

Question 18

What did De Broglie propose?

Answer 18

All matter has wave and particle like properties

Question 19

What is wave particle duality?

Answer 19

A model used to describe how all matter has wave and particle like properties

Question 20

What are matter waves?

Answer 20

Particles travelling like waves. All mass that is moving has wave like properties

It is a probability wave: the probability of finding a particle at a point is directly proportional to amplitude squared

Question 21

What is the De Broglie relationship ?

Answer 21

Wavelength=h/p

Wavelength=h/MV

Question 22

When can electrons diffract?

Answer 22

When they pass through gaps which are a similar order of magnitude to their wavelength.

Question 23

Example of electrons acting as waves and as particles

Answer 23

They diffract: waves

They are affected by fields: particle