2.6

Question 1

What makes two waves “in phase”?

Answer 1

When two waves coincide with matching peaks and throughs.

Question 2

What happens if two waves meet in phase?

Answer 2

If two waves of equal frequency meet in phase, the peaks and troughs will double in amplitude and create a maximum.

Question 3

What is the name of when two waves meet in phase?

Answer 3

Constructive interference

Question 4

What happens if two waves meet exactly out of phase?

Answer 4

If two waves of equal frequency meet exactly out of phase, these will interfere to produce a wave with zero amplitude.

Question 5

What is the name for when two waves meet exactly out of phase?

Answer 5

Destructive interference

Question 6

How can interference occur from a single source?

Answer 6

interference can occur between waves from a single source when they have travelled different distances and if the path difference between the waves is a full number of wavelengths (constructive interference) or a half number of odd wavelengths (destructive interference).

Question 7

How can interference occur from two sources?

Answer 7

Interference can occur between two wave sources provided that the waves have the same frequency and that the waves have a constant phase relationship. Sources of waves that produce waves of the same frequency and in the same phase relationship are called coherent.

Question 8

What is diffraction?

Answer 8

The ability of waves to bend around objects.

Question 9

Describe an experiment to provide evidence of the wave model of light

Answer 9

The double slit experiment involves setting up a wave source, a barrier with two slits and placing a wave detector in position.

If a beam of light is shone between the slits. The slits act as coherent sources (due to diffraction) and a wave detector can be used to observe interference patterns.

The presence of interference acts as evidence for the wave model of light.

Question 10

How do you calculate path difference in constructive interference?

Answer 10

Path difference = m~
~ = wavelength

Question 11

How do you calculate path difference in destructive interference?

Answer 11

Path difference = (m + 1/2) ~

Question 12

How does a grating compare to a double slit when investigating interference patterns?

Answer 12

Compared to double slits, gratings produce an interference pattern that has more widely spaced and fewer points of maximum intensity.

Question 13

Break down the equation dsinx = m~

Answer 13

d = spacing between lines in grating (m)
x = angle
m = order number for maximum
~ = wavelength of light (m)

Question 14

What would occur if you shine white light through gratings?

Answer 14

White light contain a range of wavelengths. Different wavelengths diffract different amounts, and so spectra are created.

There are several points of maximim intensity, called maxima. The middle maxima is white as all frequencies arrive there, whereas all of the other maxima are displayed as spectra, with blue light diffracting the least and red light diffracting the most.

Question 15

What is the relationship between angle and wavelength?

Answer 15

The larger the wavelength, the larger the angle

Question 16

What is refraction?

Answer 16

The change in speed and wavelength of a wave as it passes from one medium into another medium.

Question 17

Describe how refraction occurs, in terms of wave speed

Answer 17

When lights travels from a less dense to more dense material, wavelength and wave speed decrease. This causes light to ben towards the normal (when the angle of incidence is >0 degrees).

When light travels from a more dense to a less material, wavelength and wave speed increase. This causes light to bend away from the normal (when the angle of incidence is >0 degrees).

Question 18

What is the refractive index of a medium?

Answer 18

the ratio of the speed of light in a vacuum to the speed of light in the material.

Question 19

Break down the equation n = v1/v2

Answer 19

n = refractive index
v1 = velocity of incident wave
v2 = velocity of refracted wave

Question 20

How can you calculate refractive index of a material using the angle of incidence and angle of refraction?

Answer 20

n = sinx1/sinx2

Question 21

What equation can you use to calculate refractive index of a material using wavelength?

Answer 21

n = ~1/~2

Question 22

What is the relationship between incident frequency and refractive index?

Answer 22

The refrcative index of a medium increases as the frequency of the incident wave increases.

Question 23

What is the critical angle?

Answer 23

The angle of incidence that produces an angle of refraction of 90 degrees.

Question 24

What happens when the angle of incidence is greater than the critical angle?

Answer 24

total internal reflection

Question 25

What is the relationship between critical angle and refractive index?

Answer 25

sinx = 1/n

x = critical angle
n = refractive index

Question 26

What is the frequency of a wave?

Answer 26

the number of waves per second

Question 27

What is the period of a wave?

Answer 27

time taken for one complete wave to pass a point

Question 28

What is wave speed?

Answer 28

the distance travelled in one second

Question 29

What is the wavelength?

Answer 29

the minimum distance in which a wave repeats

Question 30

What does wave behaviour show?

Answer 30

• reflection
• refraction
• diffraction
• interference

Question 31

What is interference?

Answer 31

occurs when two or more waves are superimposed. The total effect is the sum of the waves

Question 32

What are the bright spots called?

Answer 32

Maxima

Question 33

What are the dark regions called?

Answer 33

minima