waves very detailed (help)

What is a wave?

A wave is a transfer of energy from one place to another without transfer of matter

What does "no transfer of matter" mean in waves?

Particles only vibrate about fixed positions and do not travel with the wave

Describe wave motion using a rope

A vibration at one end travels along the rope as energy while the rope itself does not move along

Describe wave motion using a spring (slinky)

Energy travels through compressions and rarefactions while coils oscillate in place

Describe wave motion in water waves

Water particles move in circular motion but energy travels across the surface

What is a wavefront?

A line joining points that are in phase (same stage of vibration)

What is wavelength?

Distance between two consecutive points in phase (e.g. crest to crest)

What is frequency?

Number of complete waves passing a point per second (Hz)

What is amplitude?

Maximum displacement from the rest position

What is wave speed?

Distance travelled per unit time by the wave

State the wave equation

v = fλ

What happens to wavelength if speed increases but frequency stays constant?

Wavelength increases

What is a transverse wave?

Wave where vibrations are perpendicular to direction of energy transfer

Give examples of transverse waves

Light waves

What is a longitudinal wave?

Wave where vibrations are parallel to direction of energy transfer

Give examples of longitudinal waves

Sound waves

What is reflection?

Bouncing of waves off a surface

What happens during reflection?

Angle of incidence = angle of reflection and wave speed does not change

What is refraction?

Change in direction of a wave due to change in speed in a different medium

What causes refraction?

Change in wave speed when entering a medium of different density

What is diffraction?

Spreading of waves as they pass through a gap or around edges

What happens to diffraction when wavelength increases?

Diffraction increases

What happens to diffraction when gap size decreases?

Diffraction increases

What happens when wavelength is similar to gap size?

Maximum diffraction occurs

How does a ripple tank demonstrate reflection?

Waves bounce off a barrier showing equal angles

How does a ripple tank demonstrate refraction?

Wave speed changes in shallow vs deep water causing bending

How does a ripple tank demonstrate diffraction?

Waves spread out after passing through a gap or edge

What is the normal?

An imaginary line drawn perpendicular to the surface at the point of incidence

What is angle of incidence?

Angle between incoming ray and normal

What is angle of reflection?

Angle between reflected ray and normal

State the law of reflection

Angle of incidence = angle of reflection

What type of image is formed in a plane mirror?

Virtual

What does virtual image mean?

Image cannot be projected onto a screen

What is angle of refraction?

Angle between refracted ray and normal

Describe refraction experiment

Light passes through a glass block and bends due to speed change

What happens when light enters a denser medium?

It slows down and bends towards the normal

What happens when light enters a less dense medium?

It speeds up and bends away from the normal

What is the critical angle?

Angle of incidence at which refracted ray is 90° to the normal

What is total internal reflection?

When light is completely reflected inside a medium

Give examples of total internal reflection

Optical fibres

Define refractive index (qualitative)

Measure of how much light slows in a medium

What is the formula for refractive index (supplement)?

n = sin i / sin r

What is another refractive index formula?

n = 1 / sin c

What is a converging lens?

Lens that brings parallel rays to a focus

What is a diverging lens?

Lens that spreads rays apart

What is focal length?

Distance from centre of lens to principal focus

What is principal axis?

Straight line passing through centre of lens

What is principal focus?

Point where parallel rays converge

Describe image formed by converging lens (far object)

Real

Describe image formed by converging lens (near object)

Virtual

Why can't virtual images be projected?

Because rays do not actually meet

What is dispersion?

Separation of white light into colours

Order of colours (low → high frequency)

Red

Which colour has longest wavelength?

Red

Which colour has shortest wavelength?

Violet

What is monochromatic light?

Light of a single frequency

What is the EM spectrum?

All electromagnetic waves arranged by frequency or wavelength

State order of EM waves

Radio → Microwave → Infrared → Visible → UV → X-ray → Gamma

What is the speed of EM waves?

3.0 × 10^8 m/s in vacuum

Why do all EM waves travel at same speed?

They are all electromagnetic radiation

Uses of radio waves

TV

Uses of microwaves

Satellite communication

Uses of infrared

Heaters

Uses of visible light

Vision

Uses of ultraviolet

Sterilisation

Uses of X-rays

Medical imaging

Uses of gamma rays

Cancer treatment

Harm of microwaves

Internal heating of body cells

Harm of infrared

Skin burns

Harm of ultraviolet

Skin cancer

Harm of X-rays and gamma rays

Cell mutation and cancer

Why are microwaves used in communication?

They can penetrate atmosphere and require small antennas

Difference between analogue and digital signals

Analogue is continuous

Advantages of digital signals

Less interference

What produces sound?

Vibrating objects

Why is sound longitudinal?

Because particles vibrate parallel to direction of wave travel

What are compressions?

Regions of high pressure where particles are close together

What are rarefactions?

Regions of low pressure where particles are spread out

What is the audible range for humans?

20 Hz to 20

Why does sound need a medium?

Because it relies on particle vibrations

What is speed of sound in air?

Approximately 330–350 m/s

How does sound speed vary?

Fastest in solids

How can you measure speed of sound?

Distance ÷ time using echo or timing methods

What affects loudness?

Amplitude (higher amplitude = louder sound)

What affects pitch?

Frequency (higher frequency = higher pitch)

What is an echo?

Reflection of sound waves

What is ultrasound?

Sound with frequency above 20 kHz

Uses of ultrasound

Medical scans

How is depth calculated using sound?

distance = speed × time ÷ 2