Wave Properties (Unit 2)

Question 1

What is diffraction?

Answer 1

• spreading out of waves when they meet obstacles, such as the edges of a slit

Question 2

What happens when the wavelength is much smaller than the size of the slit or obstacle?

Answer 2

-there is little diffraction
-the main beam spreads through less than 180°

Question 3

If wavelength is equal to or greater than the width of a slit, how do waves spread?

Answer 3

waves spread as roughly semi-circular wave fronts,

Question 4

How does two source interference occur?

Answer 4

When waves from two sources pass through the same medium at the same time, they combine together

Question 5

For two source interference to be observed clearly, the sources must have?

Answer 5

-a zero or constant phase difference
-oscillations in the same direction.

Question 6

What does young’s double split experiment show?

Answer 6

light has wave-like properties.

Question 7

What is the principle of superstition?

Answer 7

if waves from two sources occupy the same region, then the total displacement at any one point is the vector sum of their individual displacements at that point

Question 8

What happens if the path difference is a whole number (integer) of wavelengths?

Answer 8

the waves arrive at P in phase which means that constructive interference will occur.

Question 9

What happens if the path difference is a odd number of half wavelengths?

Answer 9

The waves arrive at P in antiphase which means that destructive interference will occur.

Question 10

As a result of constructive interference, the resultant wave has an increased ?

Answer 10

Amplitude

Question 11

In Young’s experiment, CONSTRUCTIVE interference will results in WHAT fringe on the screen?

Answer 11

Bright fringes

Question 12

In Young’s experiment, DESTRUCTIVE interference will results in WHAT fringe on the screen?

Answer 12

Dark fringes

Question 13

What does a diffraction grating do differently to Young’s double split?

Answer 13

-a very small slit separation makes beams (“orders”) much further apart than in Young’s experiment,
-large number of slits makes the bright beams much sharper

Question 14

Coherent sources emit what kind of waves?

Answer 14

are monochromatic with wave fronts continuous across the width of the beam

Question 15

How do we know if two sources are coherent?

Answer 15

-a constant phase relationship constantly in phase or CONSTANTLY out of phase).
- produce waves of same frequency and amplitude

Question 16

Examples of coherent sources?

Answer 16

laser, single slit aperture

Question 17

Examples of incoherent sources?

Answer 17

sunlight, light bulbs

Question 18

How can two source interference be observed?

Answer 18

two waves must be coherent
-direction of polarisation is common

Question 19

What do STATIONARY WAVES have?

Answer 19

• do not transfer energy
• the amplitude is zero at the nodes and increases to a maximum at the antinodes and decreases back to 0 at the next node
  -frequency is same for all particles except at nodes
  -all the particles between two adjacent nodes have the same phase but are in antiphase with those in the next loop

Question 20

What do PROGRESSIVE WAVES have?

Answer 20

-Progressive waves transfer energy
-Amplitude does not change
-All particles vibrate with the frequency of the wave
-all the particles within one wavelength have a different phase, between 0 and 2 pi

Question 21

What can a stationary wave be regarded as?

Answer 21

superposition of two
progressive waves of equal amplitude and frequency, travelling in opposite
directions

Question 22

What is the internodal distance?

Answer 22

Pi/2

Question 23

Wavelength of a progressive wave?

Answer 23

-the minimum distance (measured along the direction of propagation)between two points on the wave oscillating in phase.