page 1-2
1. Loud but clear

 How loud are sounds? We can produce a sound by making something vibrate. For example, a vibrating guitar string makes a sound. If you pluck the string harder, it will make a louder sound than a gentle pluck. To make a louder sound, the string vibrates with a bigger amplitude than for a quiet sound. The amplitude is how far the string moves from its normal position.
 Picture 5. Plucking a string makes it vibrate and produces a sound.
 Plotting sounds In picture 5, you can see a guitar string vibrating. Its movement is being plotted out on the graph above – as the string moves up, the graph goes up and as it moves down, the graph moves down. The amplitude is the height of the graph from the axis, i.e. the furthest the string moves from its normal position. If the string moves more, then the amplitude of the graph is bigger. This would make a louder sound.
 Deafeningly loud The loudness of a sound depends on the amplitude of the wave. The bigger the amplitude, the louder the sound. Some sounds can be so loud that they can damage the ear. This is because the huge amplitude of the sound wave makes the ear drum move back and forth too violently. This can cause instant damage – for example a burst eardrum; or it can cause damage over a long period of time. Therefore, it is extremely important that people protect their ears from loud sounds, especially when they are continuous. Factory workers will wear ear defenders that absorb sound waves and reduce the effects on the ear.
 Picture 6. A powerful pair of loudspeakers give out sound energy more quickly.
 Loudness and power A loud sound carries energy at a faster rate than a quiet sound. It is more powerful (picture 6). Power is the rate of transfer of energy. We measure power in watts. A 10 watt loudspeaker transfers 10 joules every second and is not too loud. A 100 watt loudspeaker is louder. However, because of the way our ear and brain pick up sounds, it is not 10 times louder. This is reflected in the way that we measure the loudness of sounds using the decibel scale.

 Question 1-2.

Fill in the gaps in the paragraph below. Choose the best answer in each case. Make sure you spell the first one correctly.

The loudness of a sound wave is determined by its . This is how far the wave moves from . The is the unit we use to compare the loudness of sounds.
 Summary                   Close Something vibrating makes a soundThe amplitude of the vibration determines the loudness of the sound The amplitude is the maximum displacement from the mid point