The diagram shows an area of 0.10 m² normal to a line connecting it to a point source of gamma radiation - AQA - A-Level Physics - Question 27 - 2021 - Paper 2

To calculate the number of photons passing through the area, we can use the formula for photon flux:

ext{Flux} = rac{ ext{Number of photons emitted}}{ ext{Surface area}}

Given that the source emits 5000 photons per second uniformly in all directions, the total area through which these photons can pass is the surface area of a sphere centered around the source. The surface area (A) of a sphere is given by the formula:

$A = 4\pi r^2,$

where r is the distance from the source, which is 2.0 m.

Calculating the surface area:

$A = 4\pi (2.0)^2 = 16\pi \approx 50.27 \text{ m}^2$

Now, we can calculate the flux:

$\text{Flux} = \frac{5000}{50.27} \approx 99.3 \text{ photons/m}^2\text{s}$

Once we have the flux, to find the number of photons passing through the given area (0.10 m²), we multiply the flux by the area:

$\text{Photons through area} = \text{Flux} \times \text{Area} = 99.3 \times 0.10 \approx 9.93 \text{ photons/s}$

Thus, rounding to the closest integers, the number of photons passing through the area every second is approximately 10. Therefore, the correct answer from the provided options is:

C. 10