9702/May Jun/11/2015/Q26

A wave of amplitude a has an intensity of 3.0 Wm^–2.

What is the intensity of a wave of the same frequency that has an amplitude 2a?

A 4.2 Wm^-2

B 6.0 Wm^–2

C 9.0 Wm^–2

D 12 Wm^–2

Solution:

Answer: D.

Intensity is directly proportional to the square of the amplitude.

I = ka²

3 Wm^-2 = ka²

x = k(2a)²

x = 12ka² / ka²

   = 12Wm^-2

Reference: PYQ - May/Jun 2015 Paper 11 Q26