4.4 Waves

Question 1

What is a progressive wave

Answer 1

An oscillation that travels through matter or a vacuum, transferring energy (not matter) from one place to another

Question 2

What happens to the particles in progressive waves

Answer 2

They vibrate as the wave passes through them but don’t move along with the wave

Question 3

What are the two types of progressive waves

Answer 3

Transverse and longitudinal

Question 4

What is a transverse wave and give an example

Answer 4

Where oscillations are perpendicular to direction of energy transfer

Eg EM waves

Question 5

What does a transverse wave look like

Answer 5

They have peaks / troughs at the maximum / minimum points of displacement

Question 6

What are longitudinal waves and give an example

Answer 6

Where particles oscillate parallel to direction of energy transfer

Eg sound waves

Question 7

What do longitudinal waves look like

Answer 7

Areas of compressions where particles are close together and areas of rarefaction where particles are spread out

Question 8

What is the displacement of a wave and state its units

Answer 8

The distance form the equilibrium position to the given point in a particular direction

Metres (m)

Question 9

What is the amplitude of a wave and state its units

Answer 9

The maximum displacement from its equilibrium point

Metres (m)

Question 10

What is wavelength (λ) and state its unit

Answer 10

The distance from peak to peak on a wave oscillating in phase

Metres (m)

Question 11

What is the time period (T) and state its units

Answer 11

The time taken for a full oscillation of one wavelength to pass a given point

Seconds (s)

Question 12

What is the frequency (f) and state its units

Answer 12

The number of complete oscillations passing a point per unit time

Hertz (Hz)

Question 13

What is wave speed (v) and state its units

Answer 13

The distance travelled by a wave per unit time

Metres per second (ms ^-1)

Question 14

What is phase difference and state its units

Answer 14

The difference in displacement of particles along a wave or two waves

Radians

Question 15

What is in phase

Answer 15

When the particles oscillate in sync with each other

Phase difference will be a multiple of 2π

Question 16

What is antiphase

Answer 16

When the particles are oscillating with a phase difference of an odd multiple of π

They are half a wavelength apart

Question 17

What is out of phase

Answer 17

When the particles are not moving in phase or in antiphase

Question 18

What is the equation for frequency (f)

Answer 18

Frequency (Hz) = 1 / time period (T)

f = 1/T

Question 19

What is the equation for wave speed (v)

Answer 19

Wave speed (ms ^-1) = frequency (Hz) x wavelength (m)

V = f λ

Question 20

What is reflection

Answer 20

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

Question 21

What is the relationships between the angles in reflection

Answer 21

Angle of incidence = angle of reflection

Question 22

What happens to the wavelength / frequency / wave speed in reflection

Answer 22

All stay the same

Question 23

What is refraction

Answer 23

When the wave changes direction due to a change in speed when it enters a new medium

Question 24

What happens to the wavelength / frequency and/ wave speed in a denser material in refraction

Answer 24

Wave speed - longitudinal speed up, transverse slow down
Frequency - stays the same
Wavelength - changes proportionally to wave speed

Question 25

What is diffraction

Answer 25

The spreading out of a wave for t as it passes through a gap

Question 26

How does diffraction vary with the size of the gap

Answer 26

Smaller than wavelength - no diffraction as wave doesn’t pass though Equal to wavelength - maximum diffraction Bigger than wavelength - diffraction will decrease gradually

Question 27

What happens to the wavelength / frequency / wave speed in diffraction

Answer 27

All stay the same

Question 28

What is polarisation

Answer 28

Unique to transverse waves When oscillation of the wave is restricted to only one plane (plane polarised)

Question 29

How are light waves and microwaves polarised

Answer 29

Polarising filters - when two polarising filters are perpedicular to each other they completely block light Metal grilles - free electrons in the metal bar cancel out the electric field around the grille and absorb it - the horizontal electric field passes as if the grilles are positioned vertically and vies versa

Question 30

What is intensity (I) of a progressive wave and state its units

Answer 30

The radiant power passing at a right angle per unit area Watts per metre squared (Wm ^-2)

Question 31

What are the equations for intensity (I)

Answer 31

Intensity Wm^-2) = power (W) / area (m²) I = P/A Intensity (Wm^-2) ∝ Amplitude² (m) I ∝ A²

Question 32

What are electromagnetic (EM) waves

Answer 32

Transverse waves Travel in a vacuum All travel at the speed of light in a vacuum 3.0x10⁸ ms^-1

Question 33

Name the EM waves in order from lowest frequency to highest

Answer 33

Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays

Question 34

What happens to the energy of the waves as frequency increases

Answer 34

It increased meaning the aves become more ionising and harmful to cells This is why UV, X-rays and gamma rays can cause cancer

Question 35

What is the main use of radio waves

Answer 35

Communications (radio and TV)

Question 36

What are the main uses of microwaves

Answer 36

Heating food Communications (Wi-Fi, mobile phones, satellites)

Question 37

What are the main uses of infrared

Answer 37

- remote controls - fibre optic communications - thermal imaging (medicine and industry) - night vision - heating and cooking - motion sensors

Question 38

What is the main use of visible light

Answer 38

Seeing things Taking photos or videos

Question 39

What are the main uses of UV

Answer 39

- Security marking (fluorescence) - fluorescent bulbs - tanning

Question 40

What is the main use of X-rays

Answer 40

X-ray images (medicine, industry, airport security)

Question 41

What is the main use of gamma rays

Answer 41

- sterilising medical instruments - cancer treatment

Question 42

What is the principle of superposition

Answer 42

When two or more waves with the same frequency arrive at a point, the resultant displacement in the sum of the displacements of each wave

Question 43

What is constructive interference

Answer 43

Where both displacements are in the same direction and add together

Question 44

What is destructive interference

Answer 44

Where individual displacements are in opposite directions and counteract each other leaving a flat line

Question 45

When are waves coherent

Answer 45

When they are emitted with a constant and unchanging phase difference

Question 46

What is interference

Answer 46

The superposition occurring between two coherent waves when phase difference is an event multiple of pi so the crests of the wave combine

Question 47

When does minimum resultant displacement occur

Answer 47

When phase difference is an odd multiple of pi so one crest and one trough act to cancel earth other out

Question 48

What is the equation for wavelength used in Young’s double-slit experiment

Answer 48

Wavelength (m) = ( distance between slits (m) x distance between maxima (m) ) / distance between double slits and the screen (m) λ = ax/D

Question 49

What is the equation for refractive index (n)

Answer 49

Refractive index = speed of light (ms^-1) / speed of light in medium (ms^-1) n = c/v

Question 50

What is total internal reflection

Answer 50

When no refraction occurs Light must be travelling from a medium with a higher refractive index to a lower refractive index Angle of incidence must be above the critical angle

Question 51

What is the equation to work out the critical angle (C)

Answer 51

sinC = n₂/n₁

Question 52

What is a stationary wave

Answer 52

A wave that stores energy It appears to stay in place

Question 53

How do stationary waves form

Answer 53

When two or more progressive waves superpose

Question 54

What conditions are needed to form stationary waves

Answer 54

- two progressive waves travelling in opposite directions - same frequency - almost the same amplitude - same speed

Question 55

What is a node

Answer 55

The region of the stationary wave with the displacement of zero

Question 56

What is an anode

Answer 56

The region of the stationary wave at maximum displacement

Question 57

what is the separation between adjacent nodes

Answer 57

half the wavelength λ/2

Question 58

What is the equation used in polarisation

Answer 58

Final intensity (Wm^-2) = original intensity (Wm^-2) x cos²(θ) I = I₀cos²(θ)