Waves 1

Question 1

What is a progressive wave?

Answer 1

An oscillation that travels through matter and transfers energy but not matter.

Question 2

What happens when a progressive waves travels through a medium?

Answer 2

• The particles move from their equilibrium positions to a new position
• The particles in the medium exert forces on each other
• The particles experience restoring forces from their neighbours and return to the equilibrium positions

Question 3

What are transverse waves?

Answer 3

The oscillations travel perpendicular to the direction of energy transfers.
They have peaks and troughs

Question 4

What are longitudinal waves?

Answer 4

Oscillations travel parallel to the direction of energy transfer.
Comprised of compressions (areas of high pressure) and rarefactions (areas of low pressure).

Question 5

What is displacement in a wave?

Answer 5

The distance from the equilibrium position in a particular direction, vector quantity.

Question 6

What is amplitude?

Answer 6

Max displacement from the equilibrium position, vector quantity

Question 7

What is wavelength?

Answer 7

Min distance between two points in phase on adjacent waves

Question 8

What is the period of oscillation?

Answer 8

The time taken for one oscillation or time taken for wave to move one whole wavelength past a given point

Question 9

What is frequency?

Answer 9

The number of wavelengths passing a given point per unit time

Question 10

What is wave speed?

Answer 10

The distance travelled by the wave per unit time.

Question 11

What do displacement-distance graphs show?

Answer 11

The displacement of the particles in the wave along the distance along the wave. Can be used to determine the wavelength and amplitude of both types of waves.

Question 12

What is phase difference?

Answer 12

The difference between the displacements of particles along a wave (or on different waves). Depends on the separation of particles in terms of the wavelength.

Question 13

What do displacement-time graphs show?

Answer 13

The displacement of a given particles of the medium varying with time. Looks the same for both types of waves.

Question 14

What is reflection?

Answer 14

When a wave changes direction at a boundary between two different media, remaining in the original medium.

Question 15

What is a ray?

Answer 15

The direction taken by a wave

Question 16

What is the law of reflection?

Answer 16

The angle of incidence is equal to the angle of reflection.

Question 17

What are wavefronts?

Answer 17

A line joining points of the wave which are in phase. The distance between wavefronts is equal to the wavelength of the wave.

Question 18

What is refraction?

Answer 18

When a wave changes direction as it changes speed when it passes from one medium to another

Question 19

What is partial reflection?

Answer 19

Some reflection off the surface when a wave refracts

Question 20

Where will the wave refract when it slows down?

Answer 20

Towards the normal

Question 21

Where will the wave refract when it speeds up?

Answer 21

Away from the normal

Question 22

What happens to the wavelength when the wave refracts?

Answer 22

If the wave slows down, the wavelength decreases and vice versa.

Question 23

Refraction of water waves:

Answer 23

When a water wave enters shallower water, it slows down as the wavelength gets shorter.

Question 24

What is diffraction?

Answer 24

When waves pass through a gap or travel around an obstacle, they spread out.

Question 25

What does diffraction depend on?

Answer 25

The size of the gap that the wave travels around/through. If the gap is similar to the wavelength, then the diffraction here is the largest.

Question 26

What is polarisation?

Answer 26

Polarisation is when waves are confined to a single plane, so the particles oscillate along one direction only.

Question 27

What is the plane of oscillation?

Answer 27

Contains the oscillation of the particles and the direction of travel of the wave.

Question 28

What is partial polarisation?

Answer 28

When more waves are oscillating in one particular plane, but the wave is not completely plane polarised.

Question 29

What is intensity?

Answer 29

Defined as the radiant power passing through a surface per unit area. I=P/A or I=P/4pir^2 for a wave travelling out from a source

Question 30

What is the relationship between intensity and amplitude?

Answer 30

Intensity=k(amplitude^2)
- The intensity drops as the areas increases so the amplitude decreases
- This reduces the speed and also the KE

Question 31

What are EM waves?

Answer 31

Transverse, their vibrations are changes in electrical and magnetic fields at right angles

Question 32

How to polarise EM waves?

Answer 32

With polarising filters: each filter only allows waves with a certain orientation through.

Question 33

What is refractive index?

Answer 33

n=c/v
- The angle at which the light refracts depends on the refractive index

Question 34

What is the refraction law?

Answer 34

nsintheta=k
n1sintheta1=n2sintheta2

Question 35

When does TIR occur?

Answer 35

• At the boundary between two different media when light strikes the boundary at a large enough angle to the normal.

Question 36

What are the two conditions for TIR?

Answer 36

• The light must be travelling through a medium with a higher refractive index as it strikes the boundary with a medium with a lower refractive index
• The angle at which the light strikes the boundary must be above the critical angle which depends on the refractive index of the medium

Question 37

What happens when the angle is less than the critical angle?

Answer 37

Refraction and partial reflection occurs

Question 38

What happens when the angle is equal to the critical angle?

Answer 38

Light refracts along the boundary between two different media

Question 39

What happens when the angle is larger than the critical angle?

Answer 39

TIR