• An electromagnetic wave is generated by the combined oscillation of an?electric?and a?magnetic field
• These fields oscillate?perpendicular?to each other and to the direction of motion of the wave (i.e. the direction in which energy is transferred)

An electromagnetic wave is generated by the combined oscillation of an electric and a magnetic field

• Electromagnetic waves are?transverse waves?and, as such, they can travel through?vacuum
• Regardless of their?frequency, all electromagnetic waves travel at the?speed of light?c?= 3 × 10⁸?m s^–1?in vacuum
• Electromagnetic waves form a continuous?spectrum?based on their frequency

The electromagnetic spectrum

• Humans can only sense electromagnetic waves with?wavelengths?in the range 700 nm - 400 nm, which are the limits of the so-called?visible spectrum
• Electromagnetic waves with longer and shorter wavelengths are invisible to the human eye

• Knowing the wavelengths of electromagnetic waves, their frequencies can be calculated using the?wave equation, and remembering that their speed in vacuum is always equal to the speed of light

Step 1: Write down the known quantities

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

• • • λlower?= 450 nm = 4.5 × 10^–7?m
    • λhigher?= 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 × 10⁸?m s^–1

Step 3: Write down the wave equation

c = fλ

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?flower?corresponds to the higher value of the wavelength?λhigher

= 6.1 × 10¹⁴?Hz

• • The higher frequency?fhigher?corresponds to the lower value of the wavelength?λlower

=?6.7 × 10¹⁴?Hz

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

f?= 6.1 × 10¹⁴?Hz - 6.7 × 10¹⁴?Hz