Physics IGCSE - Waves and Sound (continued)

Refraction

change in direction of a light ray passing from one medium to another

Angle of refraction

angle between the normal and the refracted ray

terms normal, angle of incidence and angle of refraction in a ray diagram

Describe the passage of light through a transparent material (boundaries between two media)

Light travels from a less dense material to a more dense material (e.g. from air to glass) → light ray bends towards the normal → angle of incidence > angle of refraction.
Light travels from a more dense material to a less dense material (e.g. from glass to water) → light ray bends away from the normal → angle of refraction > angle of incidence.

Refractive index

n → the ratio of the speeds of a wave in 2 different regions

Refractive index formula

Refractive index formula #2

speed of light in a vacuum → 3 x 10⁸ m/s

Total internal reflection

angle of incidence is greater than the critical angle → light reflects back into the medium

Critical angle

angle of incidence at which angle of refraction is 90° + above which all light is totally internally reflected

Describe total internal reflection in optical fibres

Light enters one end of optical fibre cable → undergoes total internal reflection until reaches end of cable → digital signals emitted as pulses of light → reflected along cable until reach destination

common applications of optical fibres

• telecommunications

• Broadcasting

• Medical instruments

Describe the action of a thin converging lens on a parallel beam of light

converging lens causes light rays that are travelling parallel to its principal axis to refract → cross the principal axis at fixed point called the focal point.

rays of light distance

rays of light from an object at distance → parallel

Principal axis

A line which pass through the centre of the lens

Principal focus

the point where rays of light travelling parallel to the principal axis intersect the principal axis → converge.

Focal length

distance between the centre of lens + principal focus.

Ray diagrams for the formation of an image by a thin converging lens: real images

Ray diagrams for the formation of a virtual image by a thin converging lens

Describe an image using the terms:

enlarged / same size / diminished + upright / inverted + real / virtual

use of a single lens

as a magnifying glass

dispersion of light

the refraction of white light by a glass prism

Order of the colours on the visible spectrum

Which colour has the shortest wavelength and highest frequency

violet

Which colour has the longest wavelength and the lowest frequency

red

Electromagnetic spectrum

Which ems has the longest wavelength, least amount of energy and lowest frequency

Radiowaves

Which ems has the smallest wavelength, highest frequency and highest energy

gamma rays

Speed EMS travel

same speed in a vacuum → 3.0 × 10⁸ m/s → same in the air

Uses of radio waves

radio, television transmissions + radar

Uses of microwaves

satellite television, mobile phone + microwave ovens

Uses of infrared

remote controllers for televisions + thermal imaging

Uses of visible light

vision + photograph

Uses of ultraviolet

detecting fake bank notes

Uses of X-rays

medical scanning + security scanners

Uses of gamma rays

detection of cancer + treatment

Harmful effects of ultraviolet waves

damage to surface cells and eyes → leads to skin cancer + eye conditions

Harmful effects of X-rays and gamma rays

mutation or damage to cells in the body

production of sound

produced by vibrating sources

longitudinal nature of sound waves in air

a series of compressions and rarefactions

compressions

regions of higher pressure → particles being closer together

Rarefactions as regions of lower pressure due to particles being spread further apart

regions of lower pressure → particles being spread further apart

Range of audible frequencies for a healthy human ear

20Hz to 20000Hz

How to transmit sound waves

through a medium

Determine the speed of sound in air

timing how long it takes for the sound waves to travel a known distance through a medium → stopwatch, ruler, or sonic ranger

how fast sound travels in different states of matter

faster in solids than in liquids

faster in liquids than in gases

how changes in amplitude affect loudness of sound waves

larger the amplitude → louder the sound

how changes in frequency affect the pitch of sound waves

higher the frequency → higher the pitch

Echo

reflection of a sound wave

Ultrasound range

frequency higher than 20 kHz