Photoelectric Effect and Wave Duality

Question 1

What’s threshold frequency

Answer 1

Minimum frequency of photons required to emit electrons from the surface of metal

Question 2

Describe photoelectric effect

Answer 2

When electromagnetic radiation is fired at a metal, electrons are fired out at a certain frequency of photon

Question 3

Why does the wave nature not explain photoelectric effect

Answer 3

If you had a low frequency wave and increases the intensity, the work function should be exceeded at some point

Question 4

What happens when light intensity increases

Answer 4

Number of electrons emitted increases, if frequency is higher than threshold

Question 5

What happens when frequency of light increases

Answer 5

Photoelectrons gain more kinetic energy after leaving the surface

Question 6

What are particle-sized packets of light called

Answer 6

Photons

Question 7

What is stopping potential

Answer 7

Minimum potential required to stop photoelectric emission

Question 8

What is work function

Answer 8

Minimum energy of photons required for photoelectric emission

Question 9

What is ionisation

Answer 9

When an atom gains or loses an electron

Question 10

What is excitation

Answer 10

When an electron moves to a higher energy level by collision or absorption of a “specific energy” of photon

Question 11

What happens after excitation

Answer 11

The electron de-excites to the lowest level, emitting photons at each drop

Question 12

Explain how a fluorescent tube works

Answer 12

Electrons fired at mercury atoms causing excitation. These emit UV photons in de-excitation, which is then caught by coating which excites and de-excites producing visible photons

Question 13

Describe the graph of kinetic energy (y-axis) against frequency of the photons (x-axis)

Answer 13

Linear line, x-intercept as threshold frequency, y-intercept as wave function, gradient is Planck’s Constant.
Ek = hf - ø

Question 14

What is the electron volt

Answer 14

Work done when an electron is moved through 1V of pd

Question 15

What is the lowest energy level called in an atom

Answer 15

Ground state

Question 16

What does the line spectra of hydrogen tell us

Answer 16

Evidense for transitions between discrete energy levels in atoms; hydrogen electrons de-exciting

Question 17

What suggests that particles have wave properties

Answer 17

Electron diffraction

Question 18

What is the de Broglie wavelength equation

Answer 18

wavelength = h/mv

Question 19

What happens if momentum increases

Answer 19

Voltage increases, wavelength decreases and diffraction decreases

Question 20

How are changes evaluated

Answer 20

Peer review and validated by the scientific community

Question 21

What is the equation for lasers

Answer 21

Power = nhf

Question 22

What happens if a photon hits an orbital electron that has energy, which lies between two energy levels

Answer 22

Electrons stays in the ground state as photons must lose all of there energy to excite/ionise

Question 23

What happens if an electron hits an orbital electron that has energy, which lies between two energy levels

Answer 23

The orbital electron would be excited to an energy level below that energy and the colliding electron would bounce away with the remainder energy

Question 24

What is the name of collision where kinetic energy is not conserved

Answer 24

Inelastic collision

Question 25

Explain why kinetic energy of photoelectrons range up to a certain maximum

Answer 25

photons have a fixed energy, these lose all energy in a single interactions, electrons can lose various amounts of energy to escape from the material

Question 26

What are some observations that show a particle nature of light

Answer 26

Rate of emission depends on intensity and not frequency, kinetic energy depends on frequency, existence of threshold frequency, instantaneous ejection

Question 27

Explain why wave nature of light can’t explain threshold frequency

Answer 27

Energy depends on intensity for waves, energy needed to eject electrons, you would expect emission would depend on intensity not frequency

Question 28

Explain why wave nature of light can’t explain instantaneous ejection

Answer 28

Energy is delivered continuously for waves, so low intensity wave would require a certain amount of time to gain enough energy to eject

Question 29

Explain how Einstein’s photoelectric theory accounts for threshold frequency

Answer 29

Light is made of packets called photons, these affect one electron each, they have energy E=hf, f>(theta/h) for emission

Question 30

Why are energy levels negative

Answer 30

Energy decreases from 0 as electrons move to lower energy levels