A group of students investigates the relationship between the work function of different metals and the maximum kinetic energy of the ejected electrons when the metals are irradiated with light of suitable frequency - NSC Physical Sciences - Question 11 - 2018 - Paper 1

The dependent variable is the maximum kinetic energy of the ejected electrons.

One control variable could be the wavelength of the ultraviolet light used during the investigation.

The metal with the largest work function is Silver. This is because it has the smallest maximum kinetic energy (9.19 x 10^{18} J) compared to Lead (9.28 x 10^{18} J) and Potassium (9.58 x 10^{18} J). A higher work function indicates that more energy is required to eject electrons.

Using the photoelectric equation, we have:

$E_k(max) = hf - W_0$

Where:

• $E_k(max) = 9.58 imes 10^{18} ext{ J}$ for potassium
• $h$ (Planck's constant) = $6.63 imes 10^{-34} ext{ Js}$
• $f$ (frequency) can be calculated from the wavelength $\lambda = 2 imes 10^{-8} m$, using $c = f \lambda$:

$f = \frac{c}{\lambda} = \frac{3 \times 10^8 ext{ m/s}}{2 \times 10^{-8} ext{ m}} = 1.5 \times 10^{16} ext{ Hz}$

Substituting into the equation:

The maximum kinetic energy of the photoelectrons remains the same when the intensity of the ultraviolet light increases, assuming the frequency of the light stays constant.