When distant astronomical transients such as fast radio bursts are detected there is often a time delay between the arrival time of signals at different frequencies that can give information about the distance to the source. Light from a pulsar reaches Earth after travelling through an interstellar medium with an average electron density over the path length of 10⁵ m^-³. If the pulsar emits short bursts of radiation with a bandwidth of 100 MHz at a centre frequency of 2.5 GHz and the spread of arrival times is 10 ms estimate the distance to the pulsar in light years.

When distant astronomical transients such as fast radio bursts are detected there is often a time delay between the arrival time of signals at different frequencies that can give information about the distance to the source. Light from a pulsar reaches Earth after travelling through an interstellar medium with an average electron density over the path length of 10⁵ m^-³. If the pulsar emits short bursts of radiation with a bandwidth of 100 MHz at a centre frequency of 2.5 GHz and the spread of arrival times is 10 ms estimate the distance to the pulsar in light years.