Light is incident on the cathode of a photoelectric cell connected to a battery and a sensitive ammeter, as shown below - NSC Physical Sciences - Question 10 - 2022 - Paper 1

The work function is the minimum energy required to remove an electron from the surface of a material. It is specific to each material and determines the threshold frequency of light that can cause the emission of electrons.

To calculate the maximum kinetic energy (E_k) of an ejected electron, we use the equation:

$E = hf - W_0$

where:

• $h = 6.63 \times 10^{-34} \text{ Js}$ (Planck's constant)
• $f = 5.96 \times 10^{14} \text{ Hz}$ (frequency of light)
• $W_0 = 3.42 \times 10^{-19} \text{ J}$ (work function)

Calculating:

$E_k = (6.63 \times 10^{-34} \text{ Js})(5.96 \times 10^{14} \text{ Hz}) - 3.42 \times 10^{-19} \text{ J}$ $\approx 5.30 \times 10^{-20} \text{ J}$

Using the formula for charge (q) in terms of current (I) and time (t):

$q = I \cdot t$

For a constant current of 0.012 A over 10 s:

$q = 0.012 ext{ A} \times 10 ext{ s} = 0.12 ext{ C}$

To find the number of electrons (n):

$n = \frac{Q}{e}$

where $e = 1.6 \times 10^{-19} \text{ C}$ (charge of an electron):

$n = \frac{0.12 ext{ C}}{1.6 \times 10^{-19} \text{ C/electron}} \approx 7.5 \times 10^{17} \text{ electrons}$

Since one photon can eject one electron, the minimum number of photons striking the cathode is also $7.5 \times 10^{17}$.

With an increase in the intensity of the incident light, more photons strike the cathode per unit time. As a result, more electrons will be ejected, resulting in a higher current reading on the ammeter. Therefore, the reading on the ammeter will INCREASE.