noise generated by a pair of helical gears is less than that of an equivalent pair of spur gears

Question

Assertion (A): While transmitting power between two parallel shafts the noise generated by a pair of helical gears is less than that of an equivalent pair of spur gears

Reason (R): A pair of helical gears has fewer teeth in contact as compared to an equivalent pair of spur gears.

 a) Both A and R are true and R is the correct explanation of A

 (b) Both A and R are true but R is NOT the correct

 (c) A is true but R is false

 (d) A is false but R is true

Answer 1

c.

Contact ratio of Helical gear is more than that of spur gear.

Reason for less noisy power transmission: In helical gears, small part of teeth engages at a time rather than the entire face at once.