A person at height 30 m on one bank observes light from the top of a 60 m tower across the river after reflection from the water. The reflected intensity is minimum through a polarizer, so the reflection is at Brewster angle. If μ=4/3, find the river width.

Question

G1 Physics · Accepted Answer

At Brewster reflection, tan i=μ=4/3. Let the reflection point be x from the observer-side bank and river width W. From the 30 m observer height, x/30=4/3, so x=40 m. From the 60 m tower height, (W-x)/60=4/3, so W-40=80 and W=120 m. Option A.