Tutorial 6.1: Part 1

The Wave Nature of Light: $$c = \lambda \nu\\$$

The speed of light: c

• Light can vary by its size or wavelength, but all types of light have one thing in common – they travel at a set speed – the speed of light.
• The speed of light is denoted by the letter c, and is equal to 186,000 miles/s = 300,000 km/s = $$3.00 \times 10^8 m/s$$
• The speed of light is the same regardless of the frequency of the light.
• Long wavelength radiation has lower frequency, and short wavelength radiation has higher frequency, but all radiation travels at the same speed - the speed of light.

The wavelength of light: λ

Different types of radiation have different wavelengths.

We can distinguish the different types of light by measuring the distance between consecutive peaks or consecutive valleys.

This distance is known as the wavelength. It is often abbreviated with the Greek letter "lambda" or λ .

As a distance, we can measure it in units for length, like cm, m, or nm.

The frequency of light: ν

The speed of light is not the same as the frequency.

How many peaks pass in a unit of time at some location is called the frequency of a wave.

It is measured in Hz (hertz) meaning waves per second, peaks per second, or more generally cycles per second.

We will write it as Hz, waves/second, or s-1.

It is often abbreviated with the Greek letter "nu" or ν .

If the length of the grey arrow is $$6.25 \times 10^{-7} \, m$$ what is the frequency of the blue (shorter) wave?

The wavelength of the blue wave is $$\frac{6.25 \times 10^{-7} \, m}{5} = 1.25 \times 10^{-7} \, m$$

\begin{align*} c & = \lambda\nu\\ \nu & = \frac{c}{\lambda}\\\\ \nu & = \frac{3.00 \times 10^8 \, m/s}{1.25 \times 10^{-7} \, m}\\\\ \nu & = 2.40 \times 10^{15} s^{-1} \end{align*}