A group of scientists perform an investigation by shining five different light sources A, B, C, D and E of different wavelengths onto a platinum metal surface - NSC Physical Sciences - Question 10 - 2017 - Paper 1

To find the work function (W₀) of platinum, we can use the equation W₀ = hf₀, where 'f₀' is the threshold frequency from the graph. From the graph, at the threshold frequency of approximately $1.4 \times 10^5$ Hz, we can calculate:

$W₀ = (6.63 \times 10^{-34} J.s) \times (1.4 \times 10^5 Hz)$

Calculating this gives:

$W₀ = 9.28 \times 10^{-19} J$

Each of the sub-parts regarding the number of ejected electrons should be addressed individually. In both cases:

• 10.3.1 If the intensity of light source A is increased: Remains the same
• 10.3.2 When light source B is used instead of light source A: Increase.

To calculate the speed (v) of an ejected electron when light source C (with maximum kinetic energy E_k) is used, we start with the kinetic energy equation:

$E_k = \frac{1}{2} mv^2$

From the information, we know:

• $E_k = 2 \times 10^{-18} J$\ (from the graph for light source C)
• The mass of an electron (m) is $9.11 \times 10^{-31} kg$.

Rearranging gives us:

$v = \sqrt{\frac{2E_k}{m}}$

Now substituting in the values:

= \sqrt{\frac{4 \times 10^{-18}}{9.11 \times 10^{-31}}} \ = \sqrt{4.39 \times 10^{12}} \ \approx 2.1 \times 10^6 m/s$$