Wave speed
v = f x lambda
Almost every mark lost here is a unit conversion: kHz, MHz, cm and nm all need converting first.
Know the equation
| Symbol | Quantity | Unit |
|---|---|---|
| v | wave speed | m/s |
| f | frequency | Hz |
| lambda | wavelength | m |
Rearrangements
- f = v / lambda
- lambda = v / f
Apply it — mark your own working
Work each one out on paper first, then reveal the mark scheme and tick the marks you actually earned. That is exactly how you should mark past papers.
Radio waves travel at 3.0 x 108 m/s. A radio station broadcasts at a frequency of 100 MHz. Calculate the wavelength of the radio waves.
Do the calculation on paper first — then mark it.
Where the marks get lost
- Not converting the frequency: 1 kHz = 1000 Hz, 1 MHz = 1 000 000 Hz.
- Leaving the wavelength in cm or nm; convert to metres before substituting.
- Mixing up f and lambda when rearranging — write the rearranged form out first.
Exam tip: Convert every quantity to SI units (Hz, m, m/s) on your first line. Then the number you get out is already in metres or hertz with no extra conversion.
Still losing marks on the calculations?
I'll go through your working line by line and show you exactly where the marks are — your first lesson is free.