Wave Properties

Question 1

When does diffraction occur?

Answer 1

Diffraction occurs when waves spread out after passing through a gap or around an obstacle.

Question 2

What are some features of diffraction?

Answer 2

• The narrower the gap, the more the waves spread out.

* The longer the wavelength the more the waves spread out.

Question 3

What is diffraction?

Answer 3

The way that waves spread out as they come through a narrow gap or go round obstacles.

Question 4

What does the amount of diffraction depend on?wavelengths wide.
• Most diffraction occurs when the gap is the same size as the wavelength

Answer 4

The amount of diffraction depends on the wavelength of the wave compared with the size of the gap.
• When the gap is bigger than the wavelength, diffraction is unnoticeable.
• Noticeable diffraction occurs through a gap several wavelengths wide.
• Most diffraction occurs when the gap is the same size as the wavelength
• If the gap is smaller than the wavelength, the waves are mostly reflected back.

Question 5

What happens when the gap is bigger than the wavelength?

Answer 5

Diffraction is unnoticeable.

Question 6

When do you get noticeable diffraction?

Answer 6

• Noticeable diffraction occurs through a gap several wavelengths wide.

Question 7

When does the most diffraction occur?

Answer 7

• Most diffraction occurs when the gap is the same size as the wavelength

Question 8

What happens if the gap is smaller than the wavelength?

Answer 8

• If the gap is smaller than the wavelength, the waves are mostly reflected back.

Question 9

What is required to view a clear diffraction pattern for light?

Answer 9

You need a monochromatic, coherent light source.

Question 10

What does monochromatic mean?

Answer 10

All the light has the same wavelength and frequency, and also therefore is the same colour.

Question 11

Why do waves diffract?

Answer 11

• Each point on a wavefront is a secondary emitted of wavelets.
• The wavelets from the point along a wavefront travel only in the direction in which the wave is travelling, not in the reverse direction.
• They then combine to form a new wavefront spreading beyond the gap.

Question 12

What is a wavefront?

Answer 12

A wavefront is a line or surface, in the path of a wave motion, where all the displacements at any point have the same phase

Question 13

What is reflection?

Answer 13

When straight waves directed a certain angle to hard flat surface, reflect off at the same angle.

Question 14

What is the angle between the reflected wavefront and the surface equal to?

Answer 14

• Angle between the reflected wavefront and the surface is the same as between the incident wavefront and the surface.
• Direction of the reflected wave is at the same angle to the reflector as the direction of the incident wave.

Question 15

What is a feature of the direction of a reflected wave?

Answer 15

• Direction of the reflected wave is at the same angle to the reflector as the direction of the incident wave.

Question 16

What happens when waves pass across a boundary at which the wave speed changes?

Answer 16

When the wave speed changes, the wavelength also changes.

Question 17

What happens if the wave-fronts approach at an angle to the boundary?

Answer 17

They change direction, speed and wavelength.

Question 18

What is refraction?

Answer 18

When waves change direction, speed and wavelength as they pass through a boundary.