Waves

What is a wave

A disturbance that transfers energy through oscillations

What are mechanical waves

Waves that require a medium

3 examples of mechanical waves

• Water waves

• Waves on rope

• Sound

What is amplitude (meaning, symbol, unit)

Maximum displacement from equilibrium

Symbol: A

Unit: m

What is wavelength (meaning, symbol, unit)

Distance between equivalent points on successive waves

Symbol: λ

Unit: m

What is a period (meaning, symbol, unit)

Time for a wave to complete 1 cycle

Symbol: T

Unit: s

What is frequency (meaning, symbol, unit)

Number of cycles per second

Symbol: f

Unit: Hz

What is speed (meaning, symbol, unit)

Distance travelled by wave per unit time

Symbol: v

Unit: m/s

Frequency equation

f = 1/T

Period equation

T = 1/f

Formula for wave speed

v = fλ

Formula for wave speed of electromagnetic waves in a vacuum

c = fλ

What is the value of c (speed)

3×10⁸m/s

What are transverse waves + 2 examples

Particles oscillate perpendicular to direction of propagation, e.g. waves on rope, electromagnetic waves

What are longitudinal waves + example

Particles oscillate parallel to direction of propagation, e.g. sound

What is reflection + 2 examples

Waves bounce off a barrier (e.g. echo/mirror)

What is diffraction + example

Waves bend/spread around obstacles/through openings (e.g. light under a door)

What is interference

When two or more waves combine (W1+W2=W3)

What is light

An electromagnetic wave

4 properties of electromagnetic waves

• Can travel through a vacuum

• Are transverse

• Consist of oscillating electric & magnetic fields

• Travel at 3×10⁸ m/s in vacuum

What is a photon

A quantum/particle-like unit of electromagnetic radiation

3 properties of photons

• Travel at speed of light in vacuums

• Carry energy

• Show both wave-like and particle-like behaviour

Formula for photon energy

E = hf

Where E - photon energy

h - planck’s constant (6.626×10^-34Js)

f = frequency

What can we conclude from the photon energy formula

Higher frequency, higher photon energy

what is a milli

0.001m → 1mm

what is a micro

1×10^-6m → 1μm

What is a nano

1×10^-9m → 1nm

What is a pico

1×10^-12m → 1pm

Organise the electromagnetic spectrum from longest wavelength to shortest wavelength

Radio waves → microwaves → infrared → visible → ultraviolet → x-rays → gamma rays

What are the two rules of the electromagnetic spectrum

• High frequency - high energy - low wavelength

• Low frequency - low energy - high wavelength

What can c = fλ and E = hf be combined to give

E = hc/λ

What are x-rays

Photons/electromagnetic radiation

What 3 pathways can x-rays take

• Be transmitted - pass through body

• Be scattered - change direction after interacting with matter

• Be absorbed - transfer energy to tissue

What produces radiographic image contrast

Different tissues attenuate x-rays by different amounts