Understanding how energy travels through space and matter.
Waves transfer energy from one place to another without transferring matter.
Vibrations are perpendicular ($90^\circ$) to the direction of energy transfer.
Examples: Light, Water ripples, S-waves.
Vibrations are parallel to the direction of energy transfer.
Examples: Sound, Ultrasound, P-waves.
Q1: Which type of wave requires a medium (matter) to travel through?
Mechanical waves (such as sound and water waves) require a medium.
Note: Sound waves are specifically longitudinal mechanical waves.
Q2: Describe the motion of a cork floating on water as a wave passes.
The cork moves up and down (perpendicular to the wave), but it does not move forward with the wave.
Louder sound = higher amplitude.
Higher pitch = higher frequency.
$$ v = f \times \lambda $$
What it calculates: Wave speed ($v$).
When it applies: To any wave (sound, light, water).
Common misuse: Forgetting to convert kHz to Hz or cm to m before calculating.
Q1: A wave has a frequency of 50 Hz and a wavelength of 2m. Calculate its speed.
$$ v = 50 \times 2 = 100 \, m/s $$
Q2: If the frequency of a wave increases (at constant speed), what happens to its wavelength?
The wavelength decreases (they are inversely proportional).
Law of Reflection: Angle of Incidence = Angle of Reflection.
Refraction is the change in direction of a wave when it changes speed as it crosses a boundary between materials.
Real-world Anchor: A straw in a glass of water looks "broken" because light waves slow down and bend as they enter the water.
When a wave enters a more optically dense medium (like air to glass), it slows down and bends towards the normal.
Q1: What property of a wave never changes during refraction?
The Frequency. (Only speed and wavelength change).
Q2: If a light ray hits a glass block along the 'normal' ($90^\circ$ to surface), does it bend?
No. It will change speed, but it will not change direction.
All EM waves are transverse and travel at the same speed in a vacuum ($3 \times 10^8 \, m/s$).
| Type | Hazard/Property | Typical Use |
|---|---|---|
| Radio | Lowest Energy | Television & Radio signals. |
| Microwaves | Internal heating | Satellite communication, cooking. |
| UV / X-ray | Ionising | Medical imaging, tanning. |
| Gamma | Highest Energy | Sterilising, Cancer treatment. |
Q1: Which EM waves have the shortest wavelength?
Gamma rays. Short wavelength = High frequency = High energy.
Q2: Why are X-rays and Gamma rays dangerous to humans?
They are ionising radiation, meaning they can damage DNA and cause mutations or cancer.
1. Don't say waves transfer matter; they only transfer energy and information.
2. Don't forget that "Ionising" means removing an electron from an atom.
3. Don't confuse the order of EM waves—remember: "Rich Men In Vegas Use X-ray Guns".