One end of a horizontal string is fixed to a wall. A transverse pulse moves along the string as shown.

Which of the following statements are correct for the reflected pulse compared to the forward pulse?

I.     It moves more slowly.

II.     It has less energy.

III.     It is inverted.

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

C

A surprising number of candidates chose D, perhaps thinking that if it has less energy then it must necessarily be going slower. The energy of a wave, however, is a function of its amplitude – not its velocity.

If the wall had been rigid then ‘III only’ would have been a correct response, but as this was not available, C is the only possibility and we must assume the wall is not rigid.