A pair of students measure the intensity of light from a desklamp in Sec. 4.5 of the experiment. When the detector is 25 cm from the lamp, the signal measured by the detector is 0.74 V. How large a signal (in V) do the students expect when the detector is 69 cm away?

I₂ = 0.0971 V

Explanation:

Light is an electromagnetic wave that expands uniformly throughout the space, after it is created, so that the energy is conserved, it must be distributed on the surface of the expansion sphere. The surface area of the sphere is

A = 4 π R²

The first surface has I₁ = 0.74 V with a radius of 0.25 m

I₁ = E / A₁

On the second surface that is rn r = 0.69 m

I₂ = E / A₂

Let's clear let's calculate

E = I₁ A₁ = I₂ A₂

I₁ A₁ = I₂ A₂

I₂ = I₁ A₁ / A₂

I₂ = I₁ 4 π r₁² / 4 π r₂²

I₂ = I₁ r₁² / r₂²

calculate

I₂ = 0.74 0.25² / 0.69²

I₂ = 0.0971 V