Electromagnetic radiation and quantum phenomena

Question 1

Photoelectric effect

Answer 1

Electron absorbs enough energy, breaks bonds holding it to the metal, releasing electrons (called photoelectrons)

Question 2

Photoelectric effect conclusions

Answer 2

Photoelectrons not emitted if frequency below threshold frequency.
Emitted with variety of KE.
Intensity is amount of energy per second hitting an area of metal.
No. of photoelectrons per second proportional to intensity

Question 3

Threshold frequency

Answer 3

Energy carried by wave not proportional to intensity as at low frequencies, electrons aren’t emitted

Question 4

Demonstrating Photoelectric effect

Answer 4

-vely charged zinc plate attached to top of electroscope.
Gold leaf repels and rises
US done onto plate
Electrons emitted from gold leaf. no longer -ve, no repulsion
leaf falls back down.

Question 5

Work function

Answer 5

Energy needed to break bond

Question 6

Stopping potential

Answer 6

Work done by PD to stop electrons is equal to energy being carried

Question 7

Electron volt

Answer 7

1 eV = 1.6x10⁻¹⁹ J

Question 8

Discrete energy levels

Answer 8

Electrons only exist in defined energy levels.

Electron moves down by emitting photon

Question 9

Electron transmission

Answer 9

Electron absorbs photon, moves up energy level that has exact energy difference between the 2 levels.
Excitation

Question 10

Photon emission - fluorescent tubes

Answer 10

Contain mercury vapour
High voltage supplied
Accelerates free electrons that ionise mercury atoms causing more free electrons.
Collisions cause electrons in mercury atoms to become excited and move to higher energy levels.
Mercury atoms release energy as UV photons.
Photons excite phosphorous atoms in coating/
Phosphorous atoms de-excite releasing visible photons

Question 11

Line emission spectra

Answer 11

Split light from fluorescent tube with prism or diffraction grating
Diffraction grating produces clearer lines
Line emission spectrum is series of bright lines against black background

Question 12

Line absorption spectra

Answer 12

spectrum of white light with black lines
Produced when white light passes through a cool gas
at low temp, atoms in cool gas in ground state

Question 13

Wave-particle Duality

Answer 13

All matter and energy exhibit both wave and particle like properties
Diffraction only explained using waves.
Photoelectric effect only explained by particles

Question 14

Electron diffraction

Answer 14

Electrons accelerated to high velocities in vacuum
Passed through graphite crystal
Diffracts and produces pattern of rings
Increased wavelength = increased speed
Slower electrons = wider rings
Only occurs when slit spacing is similar to wavelength