Chapter 11 and 12 - Waves

Question 1

What is a progressive wave?

Answer 1

An oscillation that travels through matter and transfers energy from one place to another.

Question 2

What are radio waves used for?

Answer 2

Communication (TV and Radio)

Question 3

What are microwaves used for?

Answer 3

Communications(Satellite, Mobile phones)

Cooking

Question 4

What is infrared used for?

Answer 4

infrared cameras
electrical heaters
remote controls

Question 5

What is visible light used for?

Answer 5

fibre optic communications

Question 6

What is ultraviolet used for?

Answer 6

Sterilisation

Question 7

What are Gamma waves used for?

Answer 7

Treating Cancer

Question 8

What is diffraction?

Answer 8

When a wave passes through a gap that is a similar size to the wave’s wavelength, the wave will spread out

Question 9

What is polarisation?

Answer 9

When a wave is made to oscillate along only one plane.

Question 10

Why can’t longitudinal waves be polarised?

Answer 10

Longitudinal waves only oscillate in one direction (the direction of energy transfer)

Question 11

Define intensity of a progressive wave

Answer 11

The radiant power passing through a surface, per unit area

Question 12

What kind of relationship does intensity have with distance?

Answer 12

An inverse square relationship

Question 13

Why does the amplitude of a wave get smaller the further it travels?

Answer 13

The further the wave travels the more spread out the energy of the wave becomes, this causes the intensity to of the wave to drop. Intensity is directly proportional to the amplitude squared so the amplitude also decreases.

Question 14

What are the conditions for total internal reflection?

Answer 14

The light must be travelling through a medium with a higher refractive index than the material it meets at the boundary.

The angle the light hits the boundary must be greater than the critical angle.

Question 15

What happens when light is travelling through a medium with a higher refractive index than the material it meets at the boundary and the angle the light hits the boundary is smaller than the critical angle?

Answer 15

refraction and partial reflection occurs.

Question 16

What happens when light is travelling through a medium with a higher refractive index than the material it meets at the boundary and the angle the light hits the boundary is the critical angle?

Answer 16

The light refracts along the boundary

Question 17

What is constructive superposition?

Answer 17

When two waves superimpose to create a wave with a greater amplitude.

Question 18

What is destructive superposition?

Answer 18

When two waves superimpose to create a wave with a smaller amplitude.

Question 19

What is coherence?

Answer 19

when two waves emitted from different sources have a constant phase difference, and therefore the same frequency.

Question 20

What happens when two waves meet at a point with a phase difference of λ?

Answer 20

The waves are in phase and will constructively superimpose.

Question 21

What happens when two waves meet at a point with a phase difference of 1/2 λ?

Answer 21

The waves are out of phase and will destructively superimpose.

Question 22

How does a stationary wave form?

Answer 22

When a progressive wave is reflected directly backwards on to itself so that the two waves superimpose to create a new wave.

Question 23

What is a node on a stationary wave?

Answer 23

A point of minimum displacement

Question 24

What is an antinode on a stationary wave?

Answer 24

A point of greatest displacement

Question 25

What is the fundamental frequency for a string?

Answer 25

The minimum frequency of a harmonic stationary wave on that string

Question 26

The frequency of each harmonic of a string with two fixed ends is...

Answer 26

A multiple of the fundamental frequency

Question 27

The frequency of each harmonic of a air column with one open end is...

Answer 27

(1/2n - 1/4) of the harmonic frequency

Question 28

The frequency of each harmonic of a air column with two open ends is...

Answer 28

1/2n of the harmonic frequency

Question 29

For a standing wave to form in an air column what must be at an open end?

Answer 29

An antinode

Question 30

For a standing wave to form in an air column what must be at a closed end?

Answer 30

A node

Question 31

Describe the set up for Young's double slit experiment.

Answer 31

In front of a monochromatic source of light there is a single narrow slit, and in front of that there is a double slit, from there the light travels towards a screen.

Question 32

Why is monochromatic light used in Young double-slit experiement?

Answer 32

So that the light arrives at the double slits in phase, as all of the waves of light have the same frequency.

Question 33

State Young's double slit experiment equation and what each symbol represents

Answer 33

Wavelength = (ax)/D a - Separation between the double slits x - Separation between fringes in the interference pattern D - Distance between screen and slits

Question 34

What did Young double-slit experiment prove?

Answer 34

The experiment demonstrates that light can form an interference pattern and so must be acting as a wave. As the waves must be superimposing to create bright and dark fringes.

Question 35

What is special about the harmonics of a standing wave in a pipe with one open end?

Answer 35

There is only odd number harmoincs

Question 36

Why do two polarising filters perpendicular to each other block all light?

Answer 36

The first filter blocks all light oscillating on the horizontal plane, so the light is oscillating vertically. When the light tries to pass through the next filter, it is blocked. As only light oscillating horizontally can pass through.

Question 37

Why does light pass through two perpendicular polarising filters, with a diagonal filter in between them?

Answer 37

Light passing through the first filter is made to oscillate vertically. When it passes through the second filter, it is oscillating vertically but there is still a vertical and horizontal component of the light, so half of the light can pass through. When the light passes through the third filter, there is a horizontal component of the light, so half of the light can pass through.

Question 38

What is the path difference of two waves?

Answer 38

The difference in wavelengths (measured in radians) between the distance travelled by the two waves.

Question 39

How long is one wavelength measured in radians?

Answer 39

2pi

Question 40

State the principle of superposition

Answer 40

When two or more waves meet at a point, the resultant displacement is equal to the sum of the displacement of each wave

Question 41

State the law of reflection

Answer 41

The angle of incidence is equal to the angle of reflection

Question 42

Whenever a wave refracts there is always some...

Answer 42

Partial reflection off the surface

Question 43

If a wave slows down when it refracts it will...

Answer 43

Refract towards the normal

Question 44

If a wave speeds up when it refracts it will...

Answer 44

Refract away from the normal

Question 45

The greater the refractive index...

Answer 45

The slower light travels through the material

Question 46

When total internal reflection happens, all...

Answer 46

light is reflected back into back into the original medium

Question 47

How can the refractive index be found from the critical angle of a material?

Answer 47

Directing a ray of light through a semi-circular block so that the light enters the block 90 degrees to the boundary. The critical angle is between the normal and the ray of light in the block.