Waves 1

Question 1

Progressive wave

Answer 1

A wave in which the peaks and troughs, or the compressions and rarefactions, move through the medium as energy is transferred e.g. P-waves (longitudinal seismic waves) and S-waves (transverse seismic waves)

Question 2

Transverse wave

Answer 2

A wave in which the medium is displaced perpendicular to the direction of energy transfer - the oscillations of the medium particles are perpendicular to the direction of travel of the wave

Question 3

Longitudinal wave

Answer 3

A wave in which the medium is displaced in the same line as the direction of energy transfer - oscillations of medium particles are parallel to the direction of the wave travel

Question 4

Displacement

Answer 4

The distance from the equilibrium position in a particular direction - displacement is a vector so it has a positive or negative value

Question 5

Amplitude

Answer 5

The maximum displacement from the equilibrium position (can be positive or negative)

Question 6

Wavelength

Answer 6

The minimum distance between two points oscillating in phase, for example the distance from one peak to the next or from one compression to the next

Question 7

Period

Answer 7

The time taken for one complete wavelength to pass a given point
OR the time taken for a particle to complete one cycle/oscillation

Question 8

Phase difference

Answer 8

The difference between the displacements of particles along a wave, or the displacements of particles on different waves, measured in degrees or radians, with each complete cycle or a difference of one wavelength representing 360˚ or 2π (360˚ = in phase; 180˚ = antiphase; anything else = out of phase)
OR
How out of phase two points on a wave are

Question 9

Frequency

Answer 9

The number of wavelengths passing a given point per unit time (f = 1/T)
OR number of cycles per second

Question 10

Speed

Answer 10

The distance travelled by the wave per unit time (v=fλ)

Question 11

Reflection

Answer 11

The change in direction of a wave at a boundary between two different media, so that the wave remains in the original medium

Question 12

Refraction

Answer 12

The change in direction of a wave as it changes speed (due to a change in density) when it passes from one medium to another

Question 13

Polarisation

Answer 13

The phenomenon in which oscillations of a transverse wave are limited to only one plane (plane polarised)
EM waves need special polarisers to be plane polarised if its electric field oscillates at random planes (unpolarised)

Question 14

Diffraction

Answer 14

The phenomenon in which waves passing through a gap or around and obstacle spread out (most observed when gap is the size of the wavelength)

Question 15

Total internal reflection

Answer 15

Reflection that occurs when:
- the light is travelling through the medium with the higher refractive index
- the incidence angle at the boundary is greater than the critical angle

Question 16

Critical angle

Answer 16

The angle of incidence at the boundary between two media that will produce an angle of refraction of 90˚ (sinC = 1/n)

Question 17

Electromagnetic wave

Answer 17

• Have oscillating electrical and magnetic components perpendicular to each other
• Travel at speed of light, c = 3x10^8, in a vacuum
• Don’t need a medium to propagate
• Transverse waves, so can be polarised

Question 18

Gamma rays

Answer 18

Short-wavelength electromagnetic waves, with wavelengths from 10^-10m to 10^-16m

Question 19

Infrared waves

Answer 19

Electromagnetic waves, with wavelengths from 10^-3m to 7x10^-7m

Question 20

Intensity

Answer 20

The radiant power passing through a surface per unit area - unit Wm^-2
- I=P/SA, where SA can be a sphere (4πr^2), so I∝1/r^2
- I∝ A^2, where A decreases due to energy spreading out

Question 21

Law of reflection

Answer 21

The angle of incidence is equal to the angle of reflection

Question 22

Microwaves

Answer 22

Long-wavelength electromagnetic waves, with wavelengths from 10^-1m to 10^-3,

Question 23

Radio waves

Answer 23

Long-wavelength electromagnetic waves, with wavelengths greater than 10^-1m

Question 24

Visible light

Answer 24

Electromagnetic waves with wavelengths from 4x10^-7m to 7x10^-7m

Question 25

X-rays

Answer 25

Short-wavelength electromagnetic waves with wavelengths from 10^-8m to 10^-13m, which can be used in medical imaging

Question 26

Refractive index

Answer 26

Measure of the bending of a ray of light when passing from one medium into another (n=c/v)

Question 27

Using an oscilloscope to determine wave frequency

Answer 27

The timebase (time interval represented by one horizontal square) for one wavelength gives the period
Using f=1/T, the frequency can be calculated with an oscilloscope (displays an electric signal in volts against a time trace)

Question 28

Law of refraction

Answer 28

Snell’s law: n1sinθ1=n2sinθ2

Question 29

Polarisation of light

Answer 29

First polaroid filter plane polarises light when held in front of the light source, then second filter when slowly rotated in front of the first filter, allows varying intensities of light, with the maximum and minimum intensities separated by a rotation of 90˚
- Malus’ Law: I = I0Cos^2θ

Question 30

Polarisation of microwaves

Answer 30

Artificially produced microwaves are already plane polarised. Can place a metal grille in front of the microwave source, to investigate the intensity of microwaves detected by the receiver

Question 31

Wave effects using a ripple tank

Answer 31

Wavelength - measure wavelength of ten ‘frozen’ waves using a metre ruler and divide by ten
Frequency - measure how long ten waves take to pass a point and divide by ten
Speed - calculate using wave equation
Refraction - slows down and wavelength shortens when wave enters shallower water

Question 32

Investigating refraction using a transparent rectangular block

Answer 32

Draw around block and a normal line at the boundary between air and glass
Direct a thin slit of light from the ray box to the normal
Draw the direction of the ray as it enters the block and as it leaves the block
Connect the points of entry and exit
Use a protractor to measure the angle of incidence and angle of refraction

Question 33

Investigate total internal reflection using a transparent semicircular block

Answer 33

Draw around block and a normal line at the centre of the boundary between glass and air
Direct a thin slit of light from the ray box to the normal, adjusting its direction until there is no light leaving the block i.e. the angle of refraction is 90˚
Use a protractor to measure the angle of incidence

Question 34

Ultraviolet

Answer 34

Electromagnetic waves with wavelengths from 4x10^-7m to 10^-8m