Waves

Understanding Waves

Amplitude describes the greatest displacement from the resting position. A larger amplitude usually means that more energy is being carried. On a guitar string, plucking harder makes the string move farther and produces a louder sound.

For sound in air, amplitude is linked to changes in pressure, which our ears interpret mainly as loudness. For light, amplitude is linked to brightness. Amplitude does not usually make a wave travel faster.

A common mistake is to confuse a tall wave drawing with a fast wave. Height shows displacement, while speed describes how quickly a particular part of the pattern moves through space.

Frequency tells how many complete vibrations occur each second. Its unit is hertz, meaning cycles per second. Period is the time taken for one complete vibration.

Frequency and period are inverses. If a source makes more vibrations each second, each vibration must take less time. This relationship is useful when reading graphs.

A displacement against time graph shows the period by measuring the horizontal distance between matching points. A displacement against distance graph shows the wavelength instead. Students often mix these graphs up because both can look like repeating curves, but their horizontal axes represent different quantities.

The material carrying a mechanical wave strongly affects its motion. A pulse on a tight string travels faster than one on a loose string because the tension pulls neighbouring parts of the string back more strongly. A heavier string tends to respond more slowly.

Sound travels at different speeds in air, water, and solids because their particles interact differently. In a solid, closely connected particles pass vibrations on efficiently. At a boundary between materials, a wave can reflect, change direction, or change wavelength.

Light bending as it enters water is a familiar example. Its frequency stays fixed because the source still sets the timing, while the speed and wavelength change in the new material.

Interference becomes especially important when waves overlap repeatedly. In noise cancelling headphones, microphones detect unwanted sound and the device produces a carefully timed sound that reduces it at the ear. Musical instruments use repeated reflections to form standing waves.

In a standing wave, some positions barely move and are called nodes, while other positions move the most and are called antinodes. Only certain wavelengths fit neatly into a guitar string, an air column, or a drum skin.

These allowed patterns create harmonics and help determine the notes an instrument can make. When solving wave problems, write down the units first, identify whether a graph uses time or distance, and check that frequency, wavelength, and speed use compatible units before calculating.