Electromagnetic Waves (DP IB Physics)

The wavelength of blue light falls within the range 450 nm – 490 nm.

Determine the range of frequencies of blue light.

Answer:

Step 1: Write down the known quantities 

• Note that you must convert the values of the wavelength from nanometres (nm) into metres (m)

• λ_lower = 450 nm = 4.5 × 10^–7 m

• λ_higher = 490 nm = 4.9 × 10^–7 m

Step 2: Remember that all electromagnetic waves travel at the speed of light in vacuum

• From the data booklet, c = 3.00 × 10⁸ m s^–1

Step 3: Write down the wave equation 

Step 4: Rearrange the above equation to calculate the frequency f 

Step 5: Substitute the lower and higher values of the wavelength to calculate the limiting values of the frequency of blue light 

• The lower frequency f_lower corresponds to the higher value of the wavelength λ_higher

• The higher frequency f_higher corresponds to the lower value of the wavelength λ_lower

Step 6: Write down the range of frequencies of blue light 

You don't need to memorise the order or the wavelengths of waves in the electromagnetic spectrum, as this is given in your data booklet. However, you must remember all electromagnetic waves travel at the speed of light, c.

You must be able to identify the features of either mechanical or electromagnetic waves, depending on the question.

A common misconception is that mechanical waves are just longitudinal, like sound waves. However, they can also be transverse waves that travel through a medium such as seismic waves (created during an earthquake) and water waves.