Unit 2 - waves

Question 1

define a wave

Answer 1

transfers energy from one point to another

Question 2

define wavelength

Answer 2

Wavelength (λ) - the distance from one point of a wave to the same point of the next wave - measured in metres (m)

Question 3

define amplitude

Answer 3

Amplitude (a) - the distance from the centre of the wave to a peak or trough - measured in metres (m)

Question 4

define the period of a wave

Answer 4

Period (T) - the time taken for one wave to pass - measured in seconds (s)

Question 5

define frequency

Answer 5

Frequency (f) - the number of waves that pass a point in one second - measured in Hz

Question 6

define wave speed

Answer 6

Wave speed (v) - the distance a wave travels in a second - measured in metres per second (ms-1)

Question 7

what are the four properties that waves show?

Answer 7

reflection, diffraction, refraction and interference.

Question 8

what is the law of reflection?

Answer 8

angle of incidence = angle of reflection - v, f and λ remain unchanged

Question 9

what is diffraction?

Answer 9

the spreading out of waves when they go through a gap, or past the edge of a barrier.

Question 10

does a low frequency diffract more or less than high frequency wave?

Answer 10

diffracts more

Question 11

what is refraction?

Answer 11

when waves change direction when passing from one medium to another due to a change in velocity. λ and v change, f stays the same.

Question 12

when does the light bend towards the normal?

Answer 12

Less dense to more dense

Question 13

what happens when white light refracts?

Answer 13

disperses into continuous spectrum (rainbow of colours) - violet light refracts more than red

Question 14

what does the amount of refraction depend on?

Answer 14

refractive index of the material

Question 15

define refractive index

Answer 15

the ratio of the speed of light in a vacuum to the speed of light in the medium (no units)

Question 16

finish this sentence: Higher the refractive index … the amount of refraction

Answer 16

higher

Question 17

with Snell’s law what must air always be?

Answer 17

sin⁡θ1

Question 18

define the critical angle?

Answer 18

the angle of incidence which produces and angle of refraction of 90 degrees.

Question 19

what is TIR?

Answer 19

occurs when the angle of incidence is greater than the critical angle - e.g. Optical fibres

Question 20

what is Interference evidence for?

Answer 20

the wave model of light

Question 21

define coherent

Answer 21

same frequency (connected to the same source) and in phase (peaks meet peaks and troughs meet troughs).

Question 22

when is maxima produced?

Answer 22

constructive interference takes place - the two waves meet in phase

Question 23

what must waves do to meet in phase?

Answer 23

must travel some distance but with a whole number of wavelengths

Question 24

when is minima produced?

Answer 24

when destructive interference takes place - the two waves meet out of phase (peaks line up with troughs)

Question 25

what must waves do to meet in phase?

Answer 25

must travel some distance but with a whole and a half wavelengths difference

Question 26

what is a diffraction grating?

Answer 26

clear window with vertical lines on it - cause light passing through to refract and the overlapping waves interfere with one another

Question 27

why is a laser a good source when using a diffraction grating?

Answer 27

the light is monochromatic (one colour, one frequency) and coherent (same frequency, same phase)

Question 28

how can you make the maxima further apart?

Answer 28

Use light with a longer wavelength, increase λ - towards the red end of the visible spectrum
Decrease d, the slit separation - have more lines per mm
Move the screen further away for the diffraction grating

Question 29

define irradiance

Answer 29

the rate at which electromagnetic energy is transferred over a given area - power per unit area

Question 30

what is irradiance measured in?

Answer 30

irradiance measured in Wm-2

Question 31

what are the reasons why the irradiance graph may not by completely accurate?

Answer 31

Other light sources in the room providing “background” irradiance
The light source may not be behaving like a point source - may look like a extended source

Question 32

what is the Bohr model of the atom?

Answer 32

Electrons occupy certain discrete energy levels. They can be excited and therefore move to a higher energy level. The electrons cannot exist between two energy levels.

Question 33

define ground state

Answer 33

lowest possible energy state of an electron

Question 34

define energy levels

Answer 34

possible energy state that an electron can occupy

Question 35

define ionisation

Answer 35

when an electron is given enough energy to escape from an atom

Question 36

define zero potential energy

Answer 36

highest possible energy state an electron can occupy while still being part of the atom

Question 37

what is continuous spectra?

Answer 37

caused by heating objects - they produce every colour form red through to violet (if at a high enough temperature)

Question 38

what is line emission spectra?

Answer 38

black with coloured lines - occurs when electrons in a higher energy level transition to a lower energy level emitting a photon

Question 39

what is absorption line spectra?

Answer 39

has black lines on a continuous spectrum - occurs when electrons in a lower energy level absorb radiation and are excited to a higher energy level

Question 40

what provides evidence for the composition of the Sun’s outer atmosphere.

Answer 40

the absorption lines (Fraunhofer lines) in the spectrum of sunlight

Question 41

how can an electron transition between energy levels?

Answer 41

by either absorbing or emitting (in the form of a proton) which matches the energy change of the electron. Only a certain transitions exist as there is only a certain number of energy levels.