Question

How is the pitch of sound in a guitar changed if:
(a) thin string is used
(b) string under less tension is used?

Answer 1

String instruments like guitar have several strings of different thickness under different tensions. Frequency (pitch) of the vibration of the string depends on the tension and thickness of the string.
(a) A note of higher pitch can be obtained by vibrating a thinner string.
(b) A note of lesser pitch can be obtained by vibrating the string under less tension.