Waves, light and sound, Year 7: more practice

Light travels much faster than sound

提示Compare the two speeds.

为什么Light travels at about 300 000 000 m/s, but sound travels at about 340 m/s in air.

35

提示The law of reflection.

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

The mirror reflects light in one direction

提示Compare how rays bounce off the two surfaces.

为什么A smooth surface reflects the rays in a regular way, but a rough surface scatters them in all directions.

The fork is vibrating

提示What is happening to the prongs when it makes a sound?

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

The drum skin

提示It is the part you hit.

为什么Hitting the skin makes it vibrate, and it makes the nearby air vibrate.

200

提示Frequency is the number of vibrations per second.

为什么1200 ÷ 6 = 200 Hz.

Higher

提示Think about which string vibrates faster.

为什么A shorter string vibrates faster, so its frequency is higher.

decibels

提示The unit is named after Alexander Graham Bell.

为什么Sound level, or loudness, is measured in decibels using a sound level meter.

Their amplitude increases

提示Which property of a wave means the size of the vibration?

为什么A 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

提示Think about how vibrations pass from one particle to the next.

为什么Close-packed particles pass vibrations on to their neighbours more quickly than those far apart in a gas.