Waves

Question 1

Progressive Wave?

Answer 1

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

Question 2

Wave Cause?

Answer 2

A wave is caused by something making particles or fields oscillate at a source

Question 3

Wave Displacement?

Answer 3

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

Question 4

Phase?

Answer 4

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

Question 5

Wave Speed Proof?

Answer 5

Let distance = λ and time taken = 1/f. Using speed = distance / time, the equation looks like: speed = λ / (1/f) which simplifies to speed = fλ

Question 6

Wave Speed from ripple tank?

Answer 6

Record depth of ripple tank. Use the dipper to create vibrations at a regular frequency. Dim lights and turn on a strobe light: a light that flashes periodically. Increase strobe light frequency until the waves appear to be standing still. This indicates the frequency of light is the same as that of the water. Measuring the distance between two adjacent peaks as that is the wavelength. Substitute the data into the wave speed equation.

Question 7

Transverse Waves?

Answer 7

The displacement of the particles or field is perpendicular to the direction of energy propagation. Examples include all EM waves and earthquake shock waves called s-waves

Question 8

Longitudinal Waves?

Answer 8

The displacement of particles or fields is parallel to the direction of energy propagation. Examples include sound waves and earthquake shock waves called p-waves

Question 9

Polarised Wave?

Answer 9

A wave which oscillates in one direction only. They can only be transverse waves

Question 10

Polarising Filters?

Answer 10

Only transmits vibrations in one direction. Light is unpolarised but when reflected off a surface is partially polarised. This allows some of it to be filtered out with a polarising filter which makes the light vibrate in the same direction and reduces the intensity in other directions. The amount of polarisation depends on the angle of incidence of the light.

Question 11

Unpolarised?

Answer 11

Vibrations are possible in all directions

Question 12

Transmitting ariels?

Answer 12

The transmitting and receiving ariel have to be aligned as otherwise the signal strength will be lower due to the signals being polarised by orientation of transmitting ariel.

Question 13

Principle of superposition?

Answer 13

When two or more waves cross the resultant displacement equals the vector sum of the individual displacements

Question 14

Destructive Interference?

Answer 14

When displacement in opposing directions cancel each other out

Question 15

Constructive Interference?

Answer 15

When displacements in the same direction combine to produce a larger displacement

Question 16

Total destructive interference?

Answer 16

Two waves of equal and opposite displacement cancel each other out completely

Question 17

In Phase?

Answer 17

Two points on a wave are in phase if they are both at the same position in the wave cycle. Points in phase will have the same displacement and velocity

Question 18

Stationary Wave?

Answer 18

Superposition of two progressive waves with the same frequency, wavelength, amplitude, phase difference and wave speed. Stationary waves don’t transmit energy

Question 19

Resonant Frequencies?

Answer 19

A specific frequency at which a system oscillates at maximum amplitude

Question 20

Nodes?

Answer 20

Points on a stationary wave where the amplitude of vibration is zero and is where total destructive interference happens

Question 21

Antinodes?

Answer 21

Points on a stationary wave where the amplitude of vibration is at a maximum, this is where constructive interference happens

Question 22

Experimentally showing stationary microwaves waves?

Answer 22

Stationary Microwaves- Have a microwave beam at a metal plate. The superposition and reflection create a standing wave, moving a probe between the plate and transmitter will allow signal variations to be measured

Question 23

Experimentally showing stationary sound waves?

Answer 23

Have powder in a tube of air, a loudspeaker being connected will produce a standing wave when connected to a signal generator and the positions where the powder concentrates most are the undisturbed nodes

Question 24

Diffraction Conditions?

Answer 24

The amount of diffraction depends on the wavelength compared to the gap. When the gap is much larger there are low amounts of diffraction. When the gap is much smaller than the wavelength most of the waves reflect back. When the gap is the same as several wavelengths there is noticeable diffraction with the most happening when the sizes are the same

Question 25

Bright Spots?

Answer 25

Where waves arrive at the screen in phase and occur from constructive interference happening

Question 26

Dark Spots?

Answer 26

Where total destructive interference occurs from waves arriving completely out of phase with each other

Question 27

Coherent Source?

Answer 27

A source that emits waves with a fixed phase difference and the same frequency and wavelength

Question 28

Diffraction pattern of white light?

Answer 28

A white central maximum but fringes of spectra of colour which aren't as clear as pattern as produced with monochromatic source. The inside of each spectra will be violet and the outside will be red

Question 29

Central Maximum trends?

Answer 29

Increasing slit width decreases the amount of diffraction meaning a narrower central maximum but more intense. Increasing wavelength increases the amount of diffraction meaning a wider central maximum with lower intensity

Question 30

Intensity?

Answer 30

Power per unit area

Question 31

Path difference?

Answer 31

The amount by which the path travelled by one wave is longer than the path travelled by the other wave

Question 32

Path difference and interference?

Answer 32

Destructive interference occurs when the path difference is a multiple of 1/2 λ wavelengths and constructive interference occurs when a whole number λ wavelengths is the path difference

Question 33

Demonstrating two source interference?

Answer 33

Have two wave sources connected to the same generator. Then have a person or use a probe if microwaves go parallel to the source and record the points of maximum loudness or signal. This will allow the positions of maxima and minima to be identified

Question 34

High Refractive Index?

Answer 34

The more optically dense a material is and the more light will slow down when it enters it.

Question 35

Relative Refractive Index?

Answer 35

The ratio of the speed of light in one material compared to an other, or is the ratio of their refractive index's

Question 36

Light changing direction at a boundary?

Answer 36

It bends towards the normal if it passes from a less optically dense material into a more optically dense material. It bends away from the normal if it passes from a more optically dense material into a less optically dense material

Question 37

Angle of incidence behaviour at boundary?

Answer 37

If the angle of incidence is the same as the critical angle the light refracts along the boundary. If greater than the critical angle total internal reflection happens. If less than the critical angle the light just refracts away from normal. These interactions only happen from a more to a less optically dense material

Question 38

Optical Fibres?

Answer 38

A thin flexible glass tube or plastic fibre that can carry signals of light over long distances and round corners from total internal reflection. They have a higher refractive index core and a lower refractive index cladding

Question 39

Benefits of optical fibres compared to electricity through cable?

Answer 39

Signals can carry more information since light has a higher frequency. Light doesn't heat fibre so it's more efficient. No electrical interference. Cheaper to produce infrastructure. The signal can travel long distances with minimal signal loss

Question 40

Signal Degradation in optical fibres?

Answer 40

Signals can be degraded through absorption or dispersion. Absorption is where some of the signal energy is absorbed by the material the fibre is made from resulting in an energy loss and amplitude of signal reducing. Dispersion is where pulse broadening occurs from signal being more spread out than initial signal resulting in pulses overlapping and creating information loss

Question 41

Dispersion in optical fibres?

Answer 41

The two types are modal dispersion and material dispersion. Modal dispersion is where light enters the fibre at different angles causing different paths to be taken and pulses arriving at different times. Material dispersion is the varying amounts of refraction experienced by different wavelengths in addition to different wavelengths varying meaning different parts of signal arrive at different time