Find the wavelength of a radio wave if the frequency is 11 x 10 ^6 Hz and the speed of radio waves in air is 3 x 10 ^8 m/s.

The key equation here is v = fL ( v is wave speed (m/s), f is frequency (Hz), L is wavelength (m)). We need to rearrange it to get L (the wavelength). To do this, we divide by f to get L = v/f. Frequency is given in the question and it already has units of Hz so that's fine already. The speed is also given so the equation is now simple! L = 3 x 10⁸ / 11 x 10⁶ = 27.273 m.Hint: This equation is easy to remember if you just think of it as a speed equation, meaning it is the same as speed = distance/time because distance is wavelength (note that the units are both metres, units of distance) and 1/time is the definition of frequency. You can also work out the equation if you forget it by looking at the units: the units for wavespeed are m/s. This means we need units of m and units of s or 1/s. This is wavelength and frequency as we have said.