Waves

Question 1

What is a progressive wave?

Answer 1

A moving wave that transfers energy from one place to another without transferring any material.

Question 2

What does it mean if a wave is reflected?

Answer 2

Bounce back when they hit a boundary.

Question 3

What does it mean when a wave refracts?

Answer 3

The wave changes direction and speed as it enters a new median

Question 4

When does it mean when a wave is diffracted?

Answer 4

Wave spreads out as it passes through a gap or round an object.

Question 5

What is displacement?

Answer 5

How far a point on the wave has moved from its undisturbed position

Question 6

What is amplitude?

Answer 6

The maximum displacement from a wave’s undisturbed position

Question 7

What is wavelength?

Answer 7

The length of one whole wave oscillation.

Question 8

What is the period?

Answer 8

Time taken for one whole wave cycle

Question 9

What is frequency?

Answer 9

Number of whole wave cycles passing a given point per second

Question 10

What is phase?

Answer 10

A measurement of the position of a certain point along the wave cycle

Question 11

What is phase difference?

Answer 11

The amount by which one wave lags behind another wave

Question 12

How do to measure the speed of sound in air?

Answer 12

• Set up 2 microphones a set distance apart connected to the same computer with different inputs so that the signals from each microphone can be picked up.
• Use a signal generator to produce a sound from a loudspeaker and use the computer to record the time between the first and second microphone picking up the sound.
• Then measure the time delay between the first peak of the signal received by each microphone on a graph of voltage against time.

Question 13

How do to measure the speed of sound in water?

Answer 13

• Use a ripple tank and measure the depth of the water using a ruler.
• Then turn on the ripple tank dipper and increase the frequency until the wave appears to not be moving ( a stationary wave is formed).
• Then use a ruler on a white piece of paper below to measure the wavelength between 2 peaks.
• Then repeat for different depths of the ripple tank.
• Use wave speed equation to calculate speed of sound in water.

Question 14

What is a transverse wave?

Answer 14

Wave oscillations move perpendicular to the direction of energy propagation

Question 15

What is a longitudinal wave?

Answer 15

Wave oscillations move parallel to the direction of energy propagation

Question 16

What is a polarised wave?

Answer 16

A wave that only oscillates in one plane.

Question 17

What is the principle of superposition?

Answer 17

When two or more waves pass through each other, the resultant displacement is equal to the vector sum of all the individual displacements

Question 18

What is a stationary wave?

Answer 18

The superposition of two progressive waves of equal frequency and amplitude but opposite direction.

Question 19

What is a node?

Answer 19

Where the amplitude of a wave equals 0

Question 20

What is an anti-node?

Answer 20

Points of maximum amplitude

Question 21

What is diffraction?

Answer 21

The spreading of waves as they pass through a gap of similar size to their wavelength.

Question 22

What does monochromatic mean?

Answer 22

One colour, single frequency

Question 23

What does coherent mean?

Answer 23

Fixed phase difference and same frequency and wavelength.

Question 24

What causes bright fringes on a diffraction pattern?

Answer 24

It is due to total constructive interference as waves arrive at a screen in phase

Question 25

What causes dark fringes on a diffraction pattern?

Answer 25

It is due to total destructive interference as waves arrive at a screen completely out of phase

Question 26

How can you increase the width of the central maxima on a diffraction pattern?

Answer 26

- Increase the wavelength of the light - Decrease the slit width

Question 27

What is Two source interference?

Answer 27

Where waves from 2 sources (superimposing) to form a constructive and destructive interference pattern.

Question 28

What is path difference?

Answer 28

It is a measure of how far ahead a wave is compared to another.

Question 29

What is a diffraction grating?

Answer 29

A slide containing many equally spaced slits very close together.

Question 30

What can Diffraction gratings be used for?

Answer 30

- Line absorption spectra - X-ray crystallography

Question 31

What is Line absorption spectra?

Answer 31

When you split up light from a star, the line absorption spectra shows you which elements are present in the star.

Question 32

What is X-ray crystallography?

Answer 32

When X-rays are directed at a thin crystal sheet, a diffraction pattern is shown. The pattern can be used to measure the atomic spacing of molecules.

Question 33

What is the refractive index?

Answer 33

It is a property of a material which measures how much it slows down light passing through it.

Question 34

What is the critical angle?

Answer 34

Where the angle of refraction is equal to 90°

Question 35

What is total internal reflection?

Answer 35

Complete reflection if a ray of light in a medium.

Question 36

What is an application of TIR?

Answer 36

Optical fibres carrying information in the form of pulses of light. - Internet data - Light can carry more information due to its high frequency - Light doesn't heat up the fibre, therefore there is very little energy dissipation - Minimal signal loss

Question 37

What are the 2 types of signal degradation?

Answer 37

- Absorption: part of the signals energy is absorbed by the fibre reducing the amplitude of the signal - Dispersion: this caused pulse broadening. Broadened signals can overlap causing a loss of information.

Question 38

What are the 2 types of Dispersion and what can be used in order to reduce this?

Answer 38

- Modal Dispersion: Because rays of light enter the fibre at different angles, some TIR more than others, leading to shorter and flatter paths. Solution: make core narrower - Material Dispersion: light of different frequencies travel at different speeds along the fibre, therefore taking different amounts of time to arrive. Solution: use monochromatic light An optical fibre repeater reduces both absorption and dispersion by regenerating the signal during its travel.

Question 39

What is the description of the pattern produced when monochromatic light passes through a very narrow slit?

Answer 39

A wide central maximum with narrower side fringes.

Question 40

A diffraction pattern is formed by passing monochromatic light through a single slit. If the width of the single slit is decreased, what happens to the width and intensity of the central maximum?

Answer 40

Intensity will decrease Width will increase.