Waves

What is a wave? A wave is some kind of disturbance that transports energy. It DOES NOT transport matter. Waves can propagate in 2 different ways:

1. Transverse Waves In a transverse wave, the energy input is perpendicular to the direction of propagation.

2. Longitudinal Waves In longitudinal waves, the energy input is parallel to the direction of propagation.

Before continuing, you need to be able to label different parts of a wave. This is a transverse wave

Wave definitions Crest: The maximum points (peaks) of the wave. Trough: The minimum points of the wave. Amplitude: The distance between the vertical midpoint and the crests (or, between the vertical midpoint and the troughs)

Definitions Wavelength: The horizontal distance between any two of the same points on the wave. For example, the horizontal distance between consecutive crests. Frequency: A measure of how many wavelengths pass by in a certain period of time.

Frequency The frequency of a wave is calculated by counting how many wavelengths pass by in a certain period of time. Each wavelength is called a cycle. The unit of frequency is called cycles/second or Hertz.

What’s the frequency? If you are watching a wave and you count 100 crests pass by in 25 seconds, what is the frequency?

What’s the frequency? Another wave passes by that has 360 000 crests pass by in 10 minutes. What’s the frequency?

What’s the frequency? You listen to the radio for 5 minutes. In that time, 28 770 000 000 crests from radio waves make their way to your radio’s antenna. What’s the frequency?

Light waves

X-rays X-rays have short wavelengths, so they can pass through your skin easily.

Electromagnetic spectrum Different wavelengths of light appear differently to us. We can see waves between 400-700 nm in wavelength as colours.

important to know The longer the wavelength in an electromagnetic wave, … The shorter the wavelength in an electromagnetic wave,…

Some questions If we increase the wavelength of a wave of coloured light, what happens? If we increase the amplitude of a wave of coloured light, what happens?

Very important to know… Electromagnetic waves do not require a medium to propagate. They can move through vacuums and outer space. Mechanical waves do require a medium to propagate.

Is sound a mechanical or electromagnetic wave?

Changing sound waves What happens when you increase the frequency of a sound wave? What happens when you increase the amplitude of a sound wave?

Remember Higher pitched notes: have higher frequency, shorter wavelength Lower pitched notes: have lower frequency, longer wavelength