Waves - Paper 1

unit of the phase of a wave

degree (°)

unit of frequency

hertz (Hz)

Longitudinal and Transverse Waves

Longitudinal: vibrations are parallel to direction wave travels, sound waves

Transverse: vibrations are perpendicular to direction wave travels, light waves

Amplitude

maximum displacement of particles from their resting or equilibrium position

Wavefront

line where all the vibrations are in phase and the same distance from the source

Frequency

number of waves produced each second by a source

Wavelength

distance between particular point on wave and same point on next wave

(Time) Period

time it takes for a source to produce one wave

Waves

transfer energy and information without transferring matter

Wave Speed Equation

wave speed = frequency x wavelength

Frequency Equation

Frequency = 1/time period

Doppler Effect (source moving away from you)

• (observed) frequency decreases

• speed of waves constant

• wavefronts behind source spread out

• causing an increased wavelength (at the observer)

• reference to f = speed ÷ wavelength

Electromagnetic Spectrum

- radio, microwaves, infrared radiation, visible light, ultraviolet, xrays, gamma rays (increasing frequency, decreasing wavelength)

- violet has highest frequency, lowest wavelength

- all transverse waves, travel at same speed in free space

Uses of Radiowaves

broadcasting and communications

Uses, Dangers and Protection of Microwaves

Uses: cooking and statellite transmissions

Dangers: internal heating of body tissue

Protection: metal walls and metal grid in glass door prevent escape

Uses, Dangers and Protection of Infrared

Uses: heaters and night vision equipment

Danger: skin burns

Protection: protective clothing (gloves)

Uses of Visible Light

Optical fibres and photography

Uses, Dangers and Protection of Ultraviolet

Uses: fluorescent lamps

Dangers: damage to surface cells and blindness

Protection: sunglasses and sunscreen

Uses of X-Rays

observing internla structure of objects and materials, including for medical applications

Uses and Dangers of Gamma Rays

Uses: sterilising food and medical equipment

Dangers: cancer, mutation

Protection: using rubber gloves when handling

Light Waves

transverse waves that can be reflected and refracted

Law of Reflection

angle of incidence = angle of reflection

Ray Diagrams

Refractive Index

n = sin i/ sin r

Refraction

ray enters denser medium → slows down → refracted towards normal

ray strikes boundary at 90° → no change in direction

Investigate the Refraction of Light

1. Draw around block on paper.

2. Mark point where light from ray box will enter block

3. Shine light into block and measure angle of incidence using protractor

4. Mark point where ray exits box.

5. Use ruler to draw path of ray

6. Measure angle of refraction

7. Repeat for different angle of incidence

Total Internal Reflection

rays of light travel towards less optically dense medium and the angle of incidence is greater than critical angle, light is reflected at boundary

Critical Angle

angle of incidence that produces an angle of refraction of 90°

Relationship between Critical Angle and Refractive Index

sin c = 1/n

Sound Waves

longitudinal waves that can be reflected and refracted