A string is made to vibrate at its third harmonic. The diagram shows two points P and Q at a particular instant in time. Which of the following compares the period of vibration of P and Q?
(The string is closed at both ends; P is just before the first maximum antinode and Q is at the next minimum antinode).
A. Period of P and Q is the same
B. Period of P and Q is different
Why is it A not B?