Physics IGCSE - Waves and Reflections

Do waves transfer matter?

Waves transfer energy without transferring matter

Transverse

vibrates at right angles to the direction of travel

Examples of transverse waves

electromagnetic radiation, water waves and seismic S - waves (secondary)

Longitudinal

vibrates parallel to the direction of travel

Examples of longitudinal waves

Sound waves and seismic P - waves (primary)

Describe what is meant by wave motion as illustrated by vibration (oscillation) in ropes and springs and by experiments using water waves

Wave motion → the transfer of energy from 1 point to another

Rope → when the rope vibrates, particles stay in fixed position → energy transferred from 1 end to the other

Frequency (f)

the number of wavelengths produced per second

UOM: hertz (Hz)

Wavelength (λ)

the distance between a point on a wave and the same point on the next wave

UOM: metres (m)

Crest

Highest point → crest

Lowest point → trough

Amplitude

Maximum displacement (distance) of the crest from the equilibrium point

Wave speed (v)

how fast the wave is moving

UOM: metres per second (m/s)

Describe how waves can undergo reflection at a plane surface

when wave hits smooth surface → reflected so that its angle of incidence equals angle of reflection

Describe how waves can undergo refraction due to a change of speed

medium its travelling through has a different density → makes the speed change → the wavelength and direction changes → wave refracts

What happens when a wave enters a more dense medium

wavelength becomes shorter and the wave speed decreases → bends toward the normal

What happens when a wave enters a less dense medium?

light wave speeds and bends away from the normal

Equation for wave speed

v = f λ

Frequency and period are inverse of each other

Reflection

change in the direction of a wave when it travels back from a barrier or the boundary between 2 different media

Refraction

change in direction of wave at boundary between 2 mediums due to a difference in wave speed between medias

Diffraction

the bending of a wave when it encounters an obstacle or a slit

Describe how waves undergo diffraction through a narrow gap

narrower gap → more diffraction occurs → waves spread out greatly → wavefronts are almost semicircular

Describe how wavelength and gap size affects diffraction through a gap

gap width similar to the wavelength of the waves passing (narrower) → more curved → less distance

gap width larger than wavelength of waves → less curved → more distance

Ray diagrams

How to compare characteristics with object in ray diagram

its orientation → inverted/upright image

if its a real or virtual image → real/virtual

the size compared to the object → diminished/larger/equal

normal

the line runs perpendicular to the mirror between 2 rays

Angle of incident

The angle of the wave approaching the boundary

Angle of reflection

The angle of the wave leaving the boundary

Diagram of an optical image by a vertical plane mirror

Law of reflection

Virtual image

cannot be projected onto a screen → appears to come from behind the lens → only be seen by looking through lens.

Real image

an image that can be projected onto a screen → rays of light actually pass through the image.

Describe the formation of an optical image by a plane mirror and explain why it is virtual

angle of incidence equals angle of reflection → light rays diverge as if they're coming from an identical but reversed object behind mirror