Question

If the energy required to remove an electron from sodium is `8.23*10^-19` `J`,, what frequency of light will cause sodium to ionize?

Answer 1

The frequency is `1.25 × 10^15color(white)(l) "Hz"`.

Explanation:

The formula for the energy of a quantum of light is

`color(blue)(bar(ul(|color(white)(a/a) E = hfcolor(white)(a/a)|)))" "`

where

`E` = energy
`h` = Planck's constant
`f` = frequency

We can rearrange the formula to get

`f = E/h`

∴ `f = (8.23 × 10^"-19" color(red)(cancel(color(black)("J"))))/(6.626 × 10^"-34" color(red)(cancel(color(black)("J")))·"s") = 1.25 × 10^15color(white)(l) "s"^"-1" = 1.25 × 10^15color(white)(l) "Hz"`