paper 2 standard answers

Question 1

stationary wave formation

Answer 1

a coherent waves of the same type moving in opposite directions
they superpose
when the waves are in phase, constructive interference occurs
leads to an area of maximum displacement called an antinode
when the waves are in antiphase, destructive interference occurs
leading to an area of minimum displacement called a node

Question 2

diffraction patterns

Answer 2

constructive interference created maxima with light waves whicha re in phase (path difference of nλ where n is an integer)
minima formed where destructive itnerference occirs - with light waves in antiphase (path difference of (n+0.5)λ)

Question 3

huygens principle

Answer 3

every point on a wavefront is a source of secondary spherical wavelets
these interfere
form new wavefront which is a tangent line across the apexes of the wavefronts

Question 4

photoelectric effect

Answer 4

light travels as particles - PHOTONS
their energy is proportional to their frequence
according to the planck equation (E=hf)
when a photon strikes the metal, it transfers all of its energy to the surface electron it strikes
if that energy is greater than the work function of the metal, the photoelectron escapes the metal
any remaining energy from the photon is transferred to the kinetic energy of the photoelectron
increasing light intensity increases the number of incident photons per second
so increases the number of photoelectrons emitted per second
therefore the current increases

Question 5

how the photoelectric effect supports particle over wave theory

Answer 5

if light were a wave:
- all frequencies would emit photoelectrons since frequency and energy are unrelated - not seen
- energy would accumulate over time allowing even dim, low frequency light to emit photoelectrons eventually. which is not seen.
- increasing the intensity of light would increase the kinetic of the photoelectrons, also not seen

Question 6

light as a particle properties

Answer 6

the energy of incident light depends on its frequency according to
one photon transfers energy to one electron - seen since photoelectrons are IMMEDIATELY emitted
below a certain threshold frequency, corresponding to the work function of the metal, no electrons would be emitted (seen)
increasing the f of the light would result in greater KE of the photoelectrons (seen)
increasing the intensity of the light would result in more photoelectrons per second and so greater current but no effect on their KE - seen

Question 7

emission spectra

Answer 7

electrons in atoms exist in discrete energy levels
the electrons become excited when they absorb energy
move to higher energy level
when they de excite move back down to lower energy level
giving out energy in the form of photons
energy of photon is equal to the energy difference between the levels
there are only certain transitions possible therefore only certain frequencies are emitted

Question 8

absorption spectra

Answer 8

if a photon equal to an energy difference in the element’s energy level is present in the light
the photon can be absorbed by the electrons
the electrons will excite and move to a higher energy level
when they de-excite, they emit the same photon in all directions
frequencies of any absorbed photons will appear to be missing from the continuous spectrum as they wull be much lower intensity

Question 9

resonance

Answer 9

the ‘driver’ forces the ‘driven system’ to oscillate at the same frequency
when the frequency of the ‘driver’ equals the natural frequency of the ‘driven system’
resonance occurs
which is maximum energy transfer from the ‘driver’
resulting in large amplitude oscillations