PHYSICS TERM 3

YEAR 10 21/04/26

WAVES

FORMULAS

Frequency=1/T(Period)

Wavespeed= FxW (frequency x wavelength)

Period= time/no. of waves

Frequency = no. of waves/time

Wave

• an oscillation or vibration that transfers energy or information from one place to another without transferring

Frequency

• Definition: The number of complete waves (cycles) passing a fixed point per second.

• Unit: Hertz (Hz).

Wavelength

• Definition: The distance between two consecutive points in phase, such as from one crest to the next, or one compression to the next.

• Unit: Metres (m).

Amplitude

• Definition: The maximum displacement (distance) of a point on the wave from its undisturbed (rest) position.

• Unit: Metres (m).

Period

• Definition: The time taken to complete one full cycle or oscillation.

• Unit: Seconds (s).

Cycle

• Definition: One complete vibration or oscillation of a wave (one full crest and one full trough)

wavefront

• is an imaginary line or surface that connects all adjacent points on a wave that are in the same phase

Longitudinal Wave

• A wave in which the particles of the medium oscillate parallel to the direction of energy transfer,

Transverse Wave

• A wave in which the oscillations of particles are perpendicular (at right angles) to the direction of energy transfer, featuring peaks and troughs.

Stationary Wave

• A wave pattern formed by the superposition of two progressive waves of the same frequency and amplitude traveling in opposite directions, resulting in no net energy transfer.

Progressive Wave

• A wave that transfers energy from one point to another through a medium (or vacuum) without the permanent transfer of matter.

Mechanical Wave

• A wave that requires a physical medium (solids, liquids, or gases) to travel

Electromagnetic Wave

• A transverse wave consisting of oscillating electric and magnetic fields that can travel through a vacuum at the speed of light.

Nodes

• are the points on a stationary wave where there is zero displacement

Antinodes

• are the points on a stationary wave where there is maximum displacement

Reflection Definition

• The bouncing back of a wave as it hits a surface or boundary.

Refraction Definition

• The bending of a wave as it moves from one medium into another due to a change in speed.

Diffraction Definition

• The spreading out of waves as they pass through a gap or move around an edge

direct propagation

• the phenomenon where energy, such as light, travels in a straight line through a uniform medium.

TYPES OF WAVES

• Longitudinal Wave

  • Sound waves

  • Slinky (pushed/pulled)

  • Tsunami waves (deep ocean)

• Transverse Wave

  • Light waves

  • Stadium "crowd" wave

  • Ripples on water

• Stationary Wave

  • Vibrating guitar string

  • Air in a whistle

  • Microwaves inside an oven

• Progressive Wave

  • Ocean waves

  • Radio signals

  • X-rays

• Mechanical Wave

  • Seismic (earthquake) waves

  • Ultrasound

  • Vibrations on a drum skin

• Electromagnetic Wave

  • Visible light

  • Wi-Fi signals

  • Gamma rays

27/04/26

INFO TO REMEMBER

milli (m) = 1/1000 = 10^-3
micro (μ) = 1/1,000,000 = 10^-6
nano (n) = 1/1,000,000,000 = 10^-9
pico (p) = 10^-12

Big values (multiples)

kilo (k) = 1000 = 10^3
mega (M) = 1,000,000 = 10^6
giga (G) = 10^9

MIRRORS

• key terms

• Real image

• Virtual image

• Eclipse

• REMEMBER - Real image is always formed upside down

Reflection is when a wave bounces off a surface. There are two main types:

• Specular Reflection: Occurs on smooth surfaces. Light rays reflect in a uniform direction.

Example: a mirror

• Diffuse Reflection: Occurs on rough surfaces. Light rays reflect in various directions.

Example: paper

CONCAVE MIRRORS

A concave mirror is a mirror that curves inward. It converges light rays, meaning it brings them together.

Key aspects of concave mirrors:

• Focal point: The point where parallel light rays converge.

• Principal axis: An imaginary line that passes through the center of the mirror and is perpendicular to its surface.

When light rays parallel to the principal axis hit a concave mirror, they are reflected to the focal point. The distance from the mirror to the focal point is called the focal length (f).

Concave mirror:
Can be upright or inverted
Can be magnified or diminished (depends on object position)

COMMON USES: Shaving/Make up Mirrors, Dentist Mirrors, Reflectors in headlights

CONVEX MIRRORS

A convex mirror curves outwards, diverging light rays away from its surface. Unlike concave mirrors, the focal point of a convex mirror is behind the mirror.

Convex mirrors always form upright, diminished, and virtual images, meaning the images appear smaller and are not formed by actual light rays converging.

Convex mirror:
Always virtual, upright, diminished (smaller than the object)

COMMON USES: Car side view mirrors, Security Mirrors, Blind corner mirrors

PLAIN MIRRORS

A plain mirror is a flat mirror that reflects light. When light hits a plain mirror, it bounces back, creating a virtual image behind the mirror. The image appears to be the same size and upright as the object.

The law of reflection applies here: the angle of incidence equals the angle of reflection (θi=θr​). This means that the image in a plain mirror is a mirror image of the object.

Plain (Plane) mirror:
Virtual, upright, same size, laterally inverted

COMMON USES: Bathroom mirrors, Periscopes, Rear - view mirrors

REFLECTION & MORE

REMEMBER

Reflection

• Angles measured from normal

• Angle of incidence = angle of reflection

Refraction

• Towards normal = slowing down

• Away from normal = speeding up

• Frequency never changes

Diffraction

• Bigger wavelength → more diffraction

• Gap similar to wavelength → maximum diffraction

Reflection

What is reflection?

Reflection is when a wave bounces off a surface.

For light:

• Smooth surfaces → clear reflection (plane mirror)

• Rough surfaces → scattered reflection

Uses of Reflection

• Mirrors

• Periscopes

• Reflectors on roads/bikes

• Telescopes

Laws of Reflection

1. Angle of incidence = angle of reflection

2. The incident ray, reflected ray and normal all lie in the same plane.

Key Words

• Incident ray = incoming ray

• Reflected ray = outgoing ray

• Normal = imaginary line at 90° to the surface

• Angles are measured from the normal, NOT the surface.

Plane Mirrors

Plane mirrors:

• Form virtual images

• Image is:

  • upright

  • same size

  • laterally inverted (left-right reversed)

  • same distance behind mirror as object is in front

2. Refraction

What is refraction?

Refraction is the change in direction of a wave when it passes from one medium to another due to a change in speed.

Examples of media:

• air

• water

• glass

Important Rule

When light:

• slows down → bends towards the normal

• speeds up → bends away from the normal

Example

Air → Glass:

• light slows down

• bends towards normal

Glass → Air:

• light speeds up

• bends away from normal

Why does refraction happen?

Because wave speed changes in different materials.

Frequency stays the same, but:

• speed changes

• wavelength changes

Refractive Index

Refractive index tells us how much light slows down in a material.

n=speed of light in vacuumspeed of light in mediumn=\frac{\text{speed of light in vacuum}}{\text{speed of light in medium}}n=speed of light in medium/speed of light in vacuum​

Higher refractive index:

• light travels slower

• more bending

Effects of Refraction

• Pencil looks bent in water

• Swimming pools appear shallower

• Lenses focus light

Total Internal Reflection (important!)

Occurs when:

1. Light travels from denser → less dense medium

2. Angle of incidence is greater than critical angle

Result:

• ALL light reflects back inside

Used in:

• optical fibres

• endoscopes

3. Diffraction

What is diffraction?

Diffraction is the spreading out of waves.

It happens most when waves:

• pass through a gap

• go around an obstacle

When is diffraction greatest?

Greatest diffraction occurs when:

• gap size ≈ wavelength

Larger wavelength:

• more diffraction

Smaller gap:

• more diffraction

Examples

• Sound heard around corners

• Water waves spreading after gaps

• Radio waves bending around buildings

REMEMBER

waves transfer energy WITHOUT transferring matter

GIZMO CORRECTIONS

When you throw a stone into a pond, which key property of the ripples determines the energy being transferred from one point to another?

• AMPLITUDE

CORRECTIONS

When water waves (or any waves) refract by moving from one medium to another

• Frequency: Stays the same because it is determined by the source of the wave.

CORRECTION - PMT 3.2 LIGHT Q.6

When a ray of light travels from a denser medium (glass) to a less dense medium (air), its behavior depends on the angle of incidence:

• At the critical angle: The light refracts along the boundary at an angle of 90°.

• Greater than the critical angle: The light cannot exit the glass. Instead, it undergoes total internal reflection, meaning the entire ray reflects back into the glass.

CORRECTION - PMT 3.2 LIGHT Q.10

The name of the process where white light is split into different colors by a prism is:

• dispersion

CORRECTION - PMT 3.2 LIGHT Q.22

When a beam of light passes through a glass prism, it undergoes dispersion. This happens because different colors of light travel at different speeds in glass, leading to different amounts of refraction

• Wavelength and Frequency: Blue light has a shorter wavelength and higher frequency than yellow light.

• Refractive Index: Glass has a higher refractive index for shorter wavelengths. Therefore, blue light bends more than yellow light.

• Direction of Bending: Light slows down entering the prism and bends toward the normal, then speeds up exiting the prism and bends away from the normal (toward the base of the prism).

If parallel light rays hit a concave mirror, at what point do they converge after reflection?

• Focal point

• Convex mirrors always form images that are upright, diminished, and virtual