Year 8 Science: Waves

• Light and sound are considered as waves
• Light travels in straight lines
• Light can be reflected in all directions by some surfaces, in one direction by mirrors
• Light can be refracted by passing into a more-dense or less-dense medium
• White light can be dispersed into a spectrum (rainbow) - we name 7 colours
• Three primary colours of light, red, green, blue, can give you any colour
• objects must reflect a colour for us to see it, otherwise we “see” black - no light!
• The speed of light is 300,000,000 m/s, that is, 300,000 kilometres per second
• Sound is a disturbance of particles in solids, liquids and gases
• Sound travels faster in liquids than gases and faster still in solids
• Sound cannot travel in a vacuum, nothing to vibrate
• Sound can be reflected as an echo
• Small objects make higher-pitched notes than larger ones
• The number of times a wave changes in a second is its frequency
• The pitch of a note is higher at a higher frequency
• The speed of sound in air is 330 m/s or about 1km in 3 seconds

• amplitude
• dispersion
• echo
• frequency
• amplitude
• normal
• pitch (of a note)
• reflection
• refraction
• spectrum
• absorb
• vibration
• transparent
• translucent
• opaque

Concept diagram:

Click here for full size image....

Reflection

When light hits a flat mirror, it reflects at an angle equal to the angle at which it comes in. The angle must be compared to the normal, an imaginary line at a right-angle to the surface.

Curved mirrors give distorted reflections, because the ray of light reflects along a different path from that which we expect. It still follows the same rule, though.

Refraction

When light enters a more dense medium, it bends towards the normal.

A and B will not be equal.

When light enters a less-dense medium, it bends away from the normal:

or:

This explains why water looks shallower than it really is, and fish seem to be nearer the surface:

Dispersion:

Light passing through a triangular prism is dispersed into a continuous spectrum having an infinite number of colours, however, only seven are named for examination purposes, the conventional spectrum:

red, orange, yellow, green, blue, indigo, violet.

Remember “Richard of York gave battle in vain”

DO NOT SING THE SONG! It contains pink, which is wrong, and the song just annoys your science teachers and classmates.