Question

At what distance will a 45 W lightbulb have the same apparent brightness as a 130 W bulb viewed from a distance of 35 m ? (Assume that both bulbs convert electrical power to light with the same efficiency, and radiate light uniformly in all directions.)

Answer 1

20.6 m

Step-by-step explanation:

P₁ = Power of first bulb = 45 W

P₂ = Power of second bulb = 130 W

r₁ = distance from the first bulb

r₂ = distance from the second bulb = 35 m

Using the equation

`(P_(1))/(r_(1)^(2)) = (P_(2))/(r_(2)^(2))`

Inserting the values

`(45)/(r_(1)^(2)) = (130)/(35^(2))`

r₁ = 20.6 m