Em Radiation And Quantum Phenomena

Question 1

What is the photoelectric effect

Answer 1

If you direct EM of a high enough frequency onto a metal it ill emit photo electrons

Question 2

Why does the photoelectric effect happen

Answer 2

Photons of high enough energy hit free electrons, if the energy of the photon is high enough then it will give the electron enough energy to break free

Question 3

What does/ does not affect ek max

Answer 3

Frequency effects it but intensity doesn’t

Question 4

How do you increase the number of photo electrons per second

Answer 4

Increase the intensity

Question 5

How does an electron move down an energy level

Answer 5

It emits photons

Question 6

Why are photon wavelength and energies discrete

Answer 6

The energy needed for an electron to move down shells is discrete and the energy levels in an atom are discrete, therefore the energy a photon has is discrete and so must its wavelength

Question 7

What’s excitation

Answer 7

When an electron absorbs the exact energy needed to move from one energy level to the next, from a photon, and it moves up to a higher energy state

Question 8

What’s ionisation energy

Answer 8

The energy needed to completely remove and electron from the fround state of an atom

Question 9

What is stopping potential

Answer 9

The potential difference needed to stop the fastest electron

Question 10

How does stopping potential work

Answer 10

The electrons lose their energy as they are made to do work against a potential difference

Question 11

What is an electron volt

Answer 11

The kinetic energy carried by an electron after it has been accelerated through a potential difference of 1v

Question 12

How many joules is in 1eV

Answer 12

1.6x10-19

Question 13

Maximum kinetic energy

Answer 13

The kinetic energy is hf, the minimum energy lost by the electron is the work function , therefore they will have a maximum kinetic energy and Ek is hf-work function

Question 14

Why do electrons emitted have different energies

Answer 14

The energy given by the photon is constant at hf, the deeper electrons the more energy it takes to escape, therefore there are different energy levels, and different kinetic energies

Question 15

What is threshold frequency

Answer 15

The minimum frequency needed for a photon to have enough energy to emit an electron

Question 16

What is the work function

Answer 16

The minimum energy an electron needs to leave the surface of a metal

Question 17

What is characteristics of wave theory

Answer 17

• for a particular frequency then E would be dp to the intensity
• energy would spread out evenly on the wavefront
• each electron would gain a fraction of the energy from a wave
• gradually an electron would escape

Question 18

Why does wave theory not work for photoelectric effect

Answer 18

The energy is dependent on intensity, but in frequency
Electrons won’t be eventually emitted
Wave theory can’t explain threshold frequency

Question 19

What is photon model of light

Answer 19

Em waves exist in discrete packets called photons

Question 20

How does photon theory explain photoelectric effect

Answer 20

E=hf which explain why energy is dependent on freuqency and it explains threshold freq
The particles have one to one interaction and there is no time delay

Question 21

How do fluorescent tubes work?

Answer 21

The contain mercury vapour and they apply a high voltage which accelerates free electrons, these ionise Mercury atoms creating more free electrons
Free electrons collide with other Mercury atoms and excite them to higher energy levels,
The de-excite emitting photons in the UV range
A phosphorus coating absorbs the photons and electrons are excited to higher orbits
Electrons cascade down the energy levels emitting lower energy photons in the form of visible light

Question 22

What’s line emission spectra and where does it occur

Answer 22

A spectrum which contains a few bright lines against a black background, these have specific wavelengths, this occurs when the light from de-exciting electrons is split using a prism or diffraction grating

Question 23

Why do line emission spectrums have specific lines

Answer 23

Each line correlates to a specific wavelength and as photons have discrete energies they have discrete wavelengths

Question 24

What’s a continuous spectra

Answer 24

Colours all merge into one an another and there are no gaps

Question 25

When does a continuous spectra occur

Answer 25

When you heat something up it will emit a continuous spectrum as all wavelengths are possible as the electrons are free and not in energy levels

Question 26

What’s a line absorption spectra

Answer 26

When you’ve a continuous spectrum but some lines are missing

Question 27

When does a line absorption spectra occur

Answer 27

When you pass light through a cool gas as the electrons will absorb photons with the right energy to excite them, the corresponding photon wavelengths are missing

Question 28

Why can light be explained as waves

Answer 28

They show interference and diffraction patters which can only be explained by waves superimposing

Question 29

Why could lib be a particle

Answer 29

The photoelectric effect uses light as a particle like photon
If a photon is a discrete bundle of energy it can interact in a 1 to 1 way
This is needed to explain why all of a photons energy is given to one electron

Question 30

How can electrons be shown as waves

Answer 30

Accelerate them in a vacuum and pass them through the spaces between graphite crystal atoms and they will create diffraction patterns

Question 31

How does wavelength effect the spread of electrons fringes

Answer 31

Increase the wavelength you can increase the spread of lines

Question 32

What happens if the electrons are slower

Answer 32

The give wider ringed and therefore diffract more

Question 33

What is peer review

Answer 33

It’s used to accept theories, you must hypothesis and validate by using an experiment that other scientist can repeat to prove the theory