Question

A gamma ray has a frequency of `2.88 * 10^21` Hz. What does this mean?

Answer 1

That means it goes through `\mathbf(2.88xx10^(21))` cycles per second. `"1 Hz = 1/s"`.

One cycle is any of the following:

• from one crest/antinode to the next crest/antinode
• from one trough to the next trough
• from one node (zero-crossing) to the next node

The equation relating frequency to wavelength and speed is:

`color(blue)(upsilon = lambdanu)`

Hence, the speed `upsilon` of a wave is the wavelength `lambda` of the wave multiplied by its frequency `nu`. If we say wavelength is in `"nm"`, then the speed is in `"nm" xx "1/s" = \mathbf("nm/s")`.

The frequency, then, is really just a measure of how fast the wave is propagating forward irrespective of knowing the wavelength.

You can further realize that we have the following equation:

`color(blue)(E = hnu)`

where we should not confuse `upsilon` with `nu`. `upsilon` is speed, while `nu` is frequency (I didn't use `f` because then I would have to redefine `nu = f`).

We can then see that a higher `nu` means a higher energy `E`. The frequency of the gamma ray is very high (it is on the order of `~10^(21)`), so the gamma ray is very strong (high-energy).