Final answer:
The intensity of light from a lightbulb can be calculated using the Inverse Square Law for Light by dividing the power of the light source by the surface area of a sphere with a radius equal to the distance from the light source.
Step-by-step explanation:
The question you've asked is related to the intensity of light and how it is calculated using the Inverse Square Law. When dealing with a point source of light like a light bulb, the intensity of light at a certain distance from the source can be found by taking the power of the light (measured in watts) and dividing it by the surface area over which the light is spread (measured in square meters). Since the light spreads out uniformly in all directions, this surface area is a sphere whose radius is the distance from the light source to the point where the intensity is being measured.
Calculating Intensity
For a 40-watt lightbulb that is 1.5 meters from a screen, the surface area of the sphere (A) with a radius (r) of 1.5 meters is A = 4πr2. Plugging in the numbers, the surface area is A = 4π(1.5)2. The intensity (I) of light incident on the screen is then calculated by dividing the power (P) of the lightbulb by the surface area (A). So I = P / A, which gives us the intensity in watts per square meter (W/m2).
The solution for the intensity at a given distance using the Inverse Square Law, employing the same principle, if the distance was changed, as given in the example, would result in a different intensity due to the increase in surface area that the light is spread over.