6: Exam Questions

Question 1

Define speed, v, for a progressive wave

Answer 1

v distance travelled by the wave per second

Question 2

derive the wave equation v = fλ which relates these terms together, (given the definitions of v, f and λ)

Answer 2

1) in 1 second f waves are produced each of one wavelength λ 2) distance travelled by first wave in one second is f λ = v

Question 3

Define Infrared radiation

Answer 3

1) infra red is part of the e-m spectrum 2) lower f or longer λ than the visible region/light or suitable value or range of λ

Question 4

Define Interference

Answer 4

1) when (two) waves meet/interact (at a point) 2) there is a change in overall intensity/displacement

Question 5

Define coherence

Answer 5

constant phase difference/relationship (between the waves)

Question 6

Explain the meaning of the term diffraction

Answer 6

paths spread out after passing through a gap or around an obstacle/

Question 7

State the condition necessary for electrons to produce observable diffraction when passing through matter, e.g. a thin sheet of graphite in an evacuated chamber.

Answer 7

1) wavelength of electrons 2) must be comparable/of the order of magnitude of the atomic spacing

Question 8

Explain how transverse waves passing along a string can produce a standing wave pattern

Answer 8

waves reflected at end/waves travelling both directions and superpose/interfere (1); to give places where they (always) superpose/interfere destructively to give zero amplitude /nodes (1); to give positions where they superpose /interfere constructively to give maximum amplitude/antinodes (1)