Waves

Question 1

What is a wave?

Answer 1

A mechanism that allows energy to be moved from one place to another.

Question 2

What is a transverse wave?

Answer 2

A wave which oscillates perpendicular to the direction of propagation and energy transfer.

Question 3

What is a longitudinal wave?

Answer 3

A wave which oscillates parallel to the direction of propagation and energy transfer.

Question 4

Give an example of a longitudinal wave.

Answer 4

Sound

Question 5

What is the main difference between transverse and longitudinal waves?

Answer 5

Transverse waves can be polarised.

Question 6

What is wavelength?

Answer 6

The distance between adjacent troughs.

Question 7

What is frequency?

Answer 7

The number of waves passing a fixed point every second.

Question 8

What is amplitude?

Answer 8

The distance between the centre line of the wave and the top of the crest.

Question 9

What is the intensity of a wave?

Answer 9

• The energy deposited per second per metre squared.

- Power deposited per metre squared.

Question 10

What is the intensity of a wave proportional to?

Answer 10

Amplitude squared

Question 11

What is phase difference?

Answer 11

The fraction of one cycle between two vibrating points.

Question 12

How can phase difference be expressed?

Answer 12

Wavelength or angle

Question 13

What is the plane of polarisation?

Answer 13

The plane of oscillation of the particles that make up the wave.

Question 14

What is the plane of polarisation for an EM wave?

Answer 14

The plane in which the electric field component vibrates.

Question 15

What type of waves are slant polarised?

Answer 15

VHF (FM) radio waves

Question 16

What is needed to form and stationary wave?

Answer 16

Two waves of the same type travelling towards each other that have the same frequency and amplitude.

Question 17

What is an antinode?

Answer 17

The maximum displacement of the envelope.

Question 18

What is a node?

Answer 18

Where the displacement of the envelope is zero.

Question 19

What is a wavefront?

Answer 19

The line drawn along the crests of waves.

Question 20

What is a ray?

Answer 20

A line drawn perpendicular to the wavefronts showing the direction of the wavefronts.

Question 21

What two rules are always observed when reflecting at a plane mirror?

Answer 21

• angle of incidence = angle of reflection

- The incident and reflected ray are in the same plane.

Question 22

What is the main use for mirrors reflecting light at 45°?

Answer 22

A periscope

Question 23

What are the three properties of an image formed in a plane mirror?

Answer 23

• The image is virtual.
• The image is the same distance behind the mirror as the object is in front.
• The image is laterally inverted.

Question 24

What is refraction?

Answer 24

The bending of a ray as it passes from one material into another and changes speed.

Question 25

What is refraction?

Answer 25

The bending of a ray as it passes from one material into another and changes speed.

Question 26

What is Snell's Law?

Answer 26

sini/sinr = 1n2 = velocity in material 1 / velocity in material 2 = n2/n1

Question 27

What does 1n2 represent?

Answer 27

The relative refractive index from material 1 into material 2.

Question 28

What does 1n2 also equal?

Answer 28

- 1 / 2n1 | - velocity in material 1 / velocity in material 2

Question 29

What is absolute refractive index?

Answer 29

The relative refractive index between a vacuum and the material.

Question 30

What is the critical angle?

Answer 30

The angle of incidence for which the angle of refraction is 90°.

Question 31

What happens if the critical angle is exceeded?

Answer 31

Total internal reflection occurs.

Question 32

What is Snell's Law at the critical angle?

Answer 32

sinic = n2/n1 = velocity in material 1 / velocity in material 2

Question 33

What is Snell's Law at the critical angle?

Answer 33

sinic = n2/n1 = velocity in material 1 / velocity in material 2

Question 34

What are the two main problems with basic fibre optics?

Answer 34

- If another material comes into contact with the fibre the boundary is no longer glass-air so the critical angle is changed meaning light can escape. - If two glass fibres touch there is no boundary meaning light can travel between the two fibres.

Question 35

How is multipath dispersion prevented?

Answer 35

Cladding made of a second layer of glass with a lower refractive index is used.

Question 36

What are the two types of fibre optic bundles used for an endoscope?

Answer 36

- Coherent bundle | - Incoherent bundle

Question 37

What type of bundle is used in an endoscope to carry light into the patient?

Answer 37

Incoherent bundle

Question 38

What type of bundle is used in an endoscope to carry light out of the patient?

Answer 38

Coherent bundle

Question 39

What is the resultant wave displacement of two waves arriving at a point?

Answer 39

The vector sum of the individual wave displacements.

Question 40

When are waves coherent?

Answer 40

If they have the same frequency or wavelength and a constant phase relationship.

Question 41

What is diffraction?

Answer 41

The bending of a wavefront as it passes through a gap or close to the edge of an object.

Question 42

What are the two types of wave interference?

Answer 42

Constructive and destructive

Question 43

How is the maximum constructive interference of a laser light calculated?

Answer 43

λ = ws / D ``` w = separation in maxima s = slit separation D = distance from slits to screen ```

Question 44

How is the width of the central maxima calculated from a single slit?

Answer 44

w = 2λD / b ``` b = slit width w = central fringe width ```

Question 45

How is the n order maxima of a diffraction grating calculated?

Answer 45

dsinθn = nλ

Question 46

When are two polarising filters "crossed"?

Answer 46

When the transmitted energy is at a mimimum.

Question 47

What is the period of a wave?

Answer 47

The time for one complete wave to pass a fixed point.

Question 48

How is phase difference calculated in radians?

Answer 48

2πd/λ

Question 49

What is superposition?

Answer 49

When two waves the total displacement is equal to the sum of the individual displacements.

Question 50

How is a microwave used to demonstrate wave properties?

Answer 50

- Moving a receiver away shows that they become weaker. - Using a metal plate shows they can be reflected. - Using a slit shows how a larger gap reduces diffraction. - Using a double slit can show interference.

Question 51

How is the distance between two adjacent nodes calculated?

Answer 51

0.5λ

Question 52

When does a light ray bend towards the normal?

Answer 52

When going into the more refractive substance

Question 53

How is the refractive index of a substance calculated?

Answer 53

sini/sinr

Question 54

What is n1sini equal to?

Answer 54

n2sinr

Question 55

From double slit interference, what does a bright fringe show?

Answer 55

The light waves from each slit are in phase.

Question 56

From double slit interference, what does a dark fringe show?

Answer 56

The two light waves are 180 out of phase

Question 57

How wide is the central fringe of single slit diffraction compared to the outer fringes?

Answer 57

It is twice as wide