Physics Yr 9

Period

The time it takes for one complete cycle of the wave

Frequency

The number of waves that pass a point in one second (measured in Hertz, Hz)

Wavelength

The distance between two consecutive crests or troughs

Amplitude

The maximum displacement from the rest position (how “tall” the wave is)

Crest

The highest point of a wave

Trough

The lowest point of a wave

Light

A type of energy that travels in waves, emitted by sources

Radiation

Any energy given off by objects as waves or particles

Why is light considered electromagnetic radiation

Because light waves are made of both electric and magnetic fields

Electromagnetic Spectrum

The full range of electromagnetic radiation

Visible light

It’s the small part of the EM spectrum humans can see (400–700 nm).

Do all EM waves travel at the same speed?

Yes, all EM waves travel at the speed of light

What determines how EM waves behave

Their wavelength (shorter wavelength = higher energy)

Order of EM spectrum (lowest to highest frequency)

Radio → Microwaves → Infrared → Visible → Ultraviolet → X-rays → Gamma rays

Example use of X-rays

Doctors use them to see inside bodies

Example use of microwaves

Heating food

Example of UV light use

Sterilizing equipment, water, or phones

The relationship between frequency and wavelength

They are inversely proportional. Formula: c = f × λ

Reflection

Light bouncing off a surface

Absorption

Light energy being taken in and transformed into heat

Transmission

Light passing through a material

Diffuse Reflection

Scattering of light off a rough surface

Regular Reflection

Light reflecting in a pattern off a smooth surface

Incidence

the intersection of a line, or something moving in a straight line, such as a beam of light, with a surface

Angle of Incidence

The angle between the incident ray and the normal

Angle of Reflection

The angle between the reflected ray and the normal

Law of Reflection

Angle of incidence = Angle of reflection

Refraction

The bending of light as it passes between different mediums

When light bends towards the normal

Entering a denser medium (e.g., air → glass)

When light bends away from the normal

Entering a less dense medium (e.g., glass → air)

Formula for refractive index (n)

n = sin(i) ÷ sin(r)

Why objects under water look shallower

Because refraction bends light away from the normal, making depth appear less

Concave Lens

Curves inward, spreads rays out (diverges)

Convex Lens

Curves outward, brings rays together (converges)

Focal Point

The point where light rays converge (convex) or appear to diverge from (concave)

Focal Length

The distance from the focal point to the lens

Example uses of convex lenses

Peepholes, projectors, correcting short-sightedness

Example uses of concave lenses

Magnifying glasses, cameras, correcting long-sightedness

The lens in the human eye

Convex Lens

Accommodation

The eye lens changing shape to focus light on the retina

Cornea

Starts bending light

Pupil

Hole that lets light in

Iris

Controls pupil size

Lens

Focuses light

Retina

Contains photoreceptors (rods & cones)

Optic nerve

Sends signals to the brain

How to correct myopia (short-sightedness)

With a concave lens

How to correct hyperopia (long-sightedness)

With a convex lens

Astigmatism

Irregularly shaped cornea/lens → corrected with special lenses

What telescopes do

Magnify distant objects

What microscopes do

Magnify very small nearby objects