3.2 Wave properties

Question 1

What is the principle of superposition?

Answer 1

The resultant displacement at each point is the vector sum of the displacements that each wave passing through the point would produce by itself

Question 2

How is interference caused?

Answer 2

When waves from more than one source or waves travelling by different paths from the same source superpose in the same region

Question 3

What makes a beam of light coherent?

Answer 3

• Nearly monochromatic i.e. it is a continuous stream of oscillations of a single frequency
• Has wavefronts extending across its width, as if it came from a point source
• Two or more sources are coherent if there is a constant phase relationship between their oscillations

Question 4

What is the equation produced by Young’s fringes experiment?

Answer 4

wavelength = ay / D, where a = separation between slits, y = fringe separation and D = distance from slits to screen

Question 5

What are nodes and antinodes?

Answer 5

In terms of a stationary wave, a node is a point of minimum amplitude and an antinode is a point of maximum amplitude

Question 6

Define internodal distance

Answer 6

The distance between nodes of a stationary wave - this is equal to half the wavelength

Question 7

Define diffraction grating constant

Answer 7

The number of slits or lines per metre. The reciprocal of this is the separation of the slits, d