Question

Observer is 3.0 m from a tiny light bulb and observer Bis 12.0 m from the same bulb. Assume that the light spreads out uniformly and undergoes no significant reflections or absorption. If observer B sees a light of intensity I, the light intensity that A sees is A) 361. BI C) 161. D) 1441. E) 91. standing wave is oscillating at 690 Hz on a string, as shown in the figure. What is the speed of veling waves on this string? 60 cm 210 m/s B) 140 m/s C) 180 m/s D) 410 m/s E) 280 m/

Answer 1

Problem - 1

Given is :-

L = 12m,l = 3m

Light intensity seen by observer B is I

Now,

The light intensity sees by observer A is

= الالم 4

P is the power of bulb which is constant at all distances, thus

Iar = 1Br}

by plugging the values we get

IA (3m)2 = (12m)

which gives us

191 = 1

This is the intensity of light seen by observer A

hence,

option - C is correct answer.