We think you are located in South Africa. Is this correct?

End Of Chapter Exercises

Practise now to improve your marks

You can do it! Let us help you to study smarter to achieve your goals. Siyavula Practice guides you at your own pace when you do questions online.

Sign up to improve your marks

Exercise 12.3

Calculate the energy of a photon of red light with a wavelength of \(\text{400}\) \(\text{nm}\).

We first calculate the energy of the photons:

\begin{align*} E & = \frac{hc}{\lambda}\\ & = \frac{(\text{3} \times \text{10}^{\text{8}})(\text{6,63} \times \text{10}^{-\text{34}})}{\text{400} \times \text{10}^{-\text{9}}}\\ & = \text{2,01} \times \text{10}^{-\text{19}}\text{ J} \end{align*}

Next convert the work function energy into J:

\begin{align*} \text{2,9} \times \text{1,6} \times \text{10}^{-\text{19}} = \text{4,64} \times \text{10}^{-\text{19}}\text{ J} \end{align*}

The energy of the photons is less than the work function of calcium and so no electrons will be emitted.

Will ultraviolet light with a wavelength of \(\text{990}\) \(\text{nm}\) be able to emit electrons from a sheet of calcium with a work function of \(\text{2,9}\) \(\text{eV}\)?

\begin{align*} E & = \frac{hc}{\lambda}\\ & = \frac{(\text{3} \times \text{10}^{\text{8}})(\text{6,63} \times \text{10}^{-\text{34}})}{\text{990} \times \text{10}^{-\text{9}}}\\ & = \text{4,97} \times \text{10}^{-\text{19}}\text{ J} \end{align*}