Energy transfer and waves
InIBDP Physics, Waves arevibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred. Think of a Mexican wave in a football crowd - the wave moves around the stadium, while each spectator stays in their seat, only moving up then down when it's their turn.
Some waves must travel through a substance. The substance is known asthe mediumand it can be solid, liquid or gas. Sound waves and seismic wavesare like this. They must travel through a medium, and it is the medium that vibrates as the waves travel through.
InIBDP Physics, Other waves do not need to travel through a substance. They may be able to travel through a medium, but they do not have to. Visible light, infrared rays,microwaves, and other types of electromagnetic radiation, are like this. They can travel through empty space. Electrical and magnetic fields vibrate as the waves travel.
As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. It is important to note that the amplitude is not the distance between the top and bottom of a wave.
In IBDP Physics, The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the trough of one wave to the crest of the next wave. But it doesn't matter where you measure it - as long as it is the same point on each wave.
In IBDP Physics, The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second.
The unit of frequency is the hertz (Hz). It is common for kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) to be used when waves have very high frequencies. For example:
- most people cannot hear a high-pitched sound above 20 kHz
- radio stations broadcast radio waves with frequencies of about 100 MHz
- most wireless computer networks operate at 2.4 GHz
The period of a wave is the time taken for one wave to be produced. It is also the time taken for one whole wave to pass a point. Period is measured in seconds.
In IBDP Physics, This is an imaginary surface that we draw to represent the vibrating part of a wave. If you draw semi-circular sound waves spreading out from a speaker, the semi-circular lines are the wavefront.
All waves, including sound waves and electromagnetic waves, follow this equation. It should be noted that some particular waves have their own specific speeds:
- the speed of light and all of the electromagnetic spectrum in a vacuum (in vacuo) is 300,000,000 m/s or 3×108m/s
- the speed of sound in air is 340 m/s
In IBDP Physics, The frequency of a wave can be calculated using this equation:
frequency = 1/ time period
f is the number of waves produced by a source per second, it is measured in hertz (Hz).
T is the time it takes for one complete oscillation, it is measured in seconds.
All waves, including sound waves and electromagnetic waves, follow this equation. For example, a wave with a time period of 2 seconds has a frequency of 1 ÷ 2 = 0.5 Hz.
This is the end of this topic.