Wave properties

Question 1

What is reflection?

Answer 1

When the angle of incidence and angle of reflection are equal.

Question 2

What is refraction?

Answer 2

The change in direction of a wave at the boundary between two materials. This is caused by a change in speed.

Question 3

Describe refraction in water

Answer 3

When waves move from shallow to deep water, their speed increase and they change direction away from the normal. Frequency stays the same.

Question 4

What is diffraction?

Answer 4

The spreading of a wave when it meets an obstacle into reigons where it would be seen if it moved only in straight lines. Wavelength remains unchanged.

Question 5

What is the principle of superposition?

Answer 5

If waves from two sources occupy the same region, then the total displacement at a point is the vector sum of the displacements of the individual waves at the point.

Question 6

What causes constructive interference?

Answer 6

If two waves arrive at a point in phase with the same frequency, they will interfere constructively.

Question 7

What causes destructive interference?

Answer 7

If two waves are out of phase, the resultant wave will have a smaller amplitude and they will interfere destructively.

Question 8

Describe the principles of observing interference

Answer 8

To observe interference, the two waves sources must be coherent and get a meaningful resultant wave by using the principle of superposition.

Question 9

What is coherence?

Answer 9

A wave is coherent if it has a constant phase difference (therefore frequency is the same).

Question 10

Give an example of a coherent light source

Answer 10

A laser.

Question 11

Give an example of an incoherent light source

Answer 11

Car headlights and normal light bulb.

Question 12

Describe coherent sources

Answer 12

Coherent sources are monochromatic with wavefronts continuous across the width of the beam and with a constant phase relationship.

Question 13

What is the path difference of waves?

Answer 13

A measure of the distance between two waves arriving at a point in terms of their wavelength.

Question 14

How can two source interference be demonstrated?

Answer 14

Using sound waves, microwaves or a laser.

Question 15

What are the principles of two source interference?

Answer 15

The sources must have zero or constant phase difference and have oscillations in the same direction.

Question 16

What do bright fringes signify in Youngs double slit experiment?

Answer 16

Constructive interference.

Question 17

What do dark fringes signify in Youngs double slit experiment?

Answer 17

Destructive interference.

Question 18

What is a diffraction grating?

Answer 18

A plate on which there is a very large number of parallel, identical, very closely spaced slits.

Question 19

What is monochromatic light?

Answer 19

Light of a single frequency.

Question 20

What is a stationary wave?

Answer 20

A pattern of disturbances in a medium, in which energy is not propagated.

Question 21

Describe a stationary wave

Answer 21

The amplitude of particle oscillations is zero at equally spaced nodes, rising to maxima at antinodes.

Question 22

How are stationary waves produced?

Answer 22

They are produced from the superposition of two progressive waves of equal amplitude and frequency, travelling in opposite directions.