Question

A photon has energy of 20keV. What are its frequency and wavelength?​

Answer 1

So we know that: E = h*(frequency)

but for this equation, we need energy in joules

so since 1eV is 1.6 *
`10^(-19)`

we will multiply the energy in eV to 1.6 * 10^-19

so energy in joules:

20000 * 1.6 * 10^-19

3.2 *
`10^(-15)` j

Now, finding the frequency:

3.2 * 10^-15 = 6.6 *
`10^(-34)` * frequency

frequency = (3.2 *
`10^(-15)`) / (6.6 *
`10^(-34)`)

frequency = 4.8 *
`10^(18)` Hz

Finally, finding the wavelength:

we will use a different formula here,

frequency * wavelength = speed of light

wavelength = speed of light / frequency

wavelength = 3 *
`10^(8)` / 4.8 *
`10^(18)`

wavelength = 3 *
`10^(-10)` / 4.8

wavelength = 0.625 *
`10^(-10)`

wavelength = 6.25 *
`10^(-11)` m

frequency = 4.8 *
`10^(18)` Hz