1.Give one reason why Huygens’ wave theory of light did not replace Newton’s theory of light when the fringe pattern due to double slits was first observed. (1)
2.The interference fringe pattern observed by M’n’M on their interferometer did not shift when the apparatus was rotated by 90°. Explain the significance of this null observation. (1)
3. Discuss the significance of Einstein’s explanation of the photoelectric effect. (2)
4. Millikan found that the charge on an oil droplet was always in multiples of e. Explain the significance of this result. (1)
5. What was the significance of Thompson’s calculations of the specific charge of an electron? (2)
Answers
1.Newton’s scientific pre-eminence/ reputation
No evidence that light travelled slower in water or glass
(as predicted by Huygens’ theory)
Huygens’ theory considered light waves as longitudinal
and therefore could not explain polarisation(1)
No evidence that light travelled slower in water or glass
(as predicted by Huygens’ theory)
Huygens’ theory considered light waves as longitudinal
and therefore could not explain polarisation(1)
2.The speed of light does not depend on the motion of the light source or of the observer(1)
3.the photon is the quantum of em radiation/light (1)
classical wave theory could not explain threshold frequency (1)
classical wave theory was replaced by the photon theory (1)
[or photons can behave as waves or particles]
classical wave theory could not explain threshold frequency (1)
classical wave theory was replaced by the photon theory (1)
[or photons can behave as waves or particles]
4.Shows that charge is quantised – comes in “packets” of 1.6 x 10-19C
5.Bigger than any specific charge measured before; 1840 x bigger than that of H nucleus; therefore electron is very small (or has huge charge)