A small potassium foil is placed (perpendicular to the direction of incidence of light) a distance `r( =0.5 m)` from a point light source whose output power `P_(0)` is `1.0W`. Assuming wave nature of light how long would it take for the foil to soak up enough energy `(=1.8eV)` from the beam to eject an electron? Assume that the ejected photoelectron collected its energy from a circular area of the foil whose radius eqals the radius of a potassium atom `(1.3xx10^(-10)m)`

Explanation

To solve the problem step-by-step, we will follow these steps:

### Step 1: Calculate the Intensity of the Light Source
The intensity (I) of the light from a point source is given by the formula:

\[ I = \frac{P_0}{A} \]
...