Waves, light and sound, Year 7: more practice

Light travels much faster than sound

HintCompare the two speeds.

The whyLight travels at about 300 000 000 m/s, but sound travels at about 340 m/s in air.

35

HintThe law of reflection.

The whyThe angle of incidence equals the angle of reflection, measured from the normal.

The mirror reflects light in one direction

HintCompare how rays bounce off the two surfaces.

The whyA smooth surface reflects the rays in a regular way, but a rough surface scatters them in all directions.

The fork is vibrating

HintWhat is happening to the prongs when it makes a sound?

The whySounds are made by vibrations. The splash shows the fork is moving quickly to and fro.

The drum skin

HintIt is the part you hit.

The whyHitting the skin makes it vibrate, and it makes the nearby air vibrate.

200

HintFrequency is the number of vibrations per second.

The why1200 ÷ 6 = 200 Hz.

Higher

HintThink about which string vibrates faster.

The whyA shorter string vibrates faster, so its frequency is higher.

decibels

HintThe unit is named after Alexander Graham Bell.

The whySound level, or loudness, is measured in decibels using a sound level meter.

Their amplitude increases

HintWhich property of a wave means the size of the vibration?

The whyA harder hit makes bigger vibrations, so a greater amplitude and a louder sound. The pitch stays the same.

The particles in a solid are closer together

HintThink about how vibrations pass from one particle to the next.

The whyClose-packed particles pass vibrations on to their neighbours more quickly than those far apart in a gas.