Question

Light from a mains powered fluorescent lamp is falling on a gear rotating clockwise. The gear wheel has one tooth painted white. The white tooth appears to be rotating in the anti-clockwise direction with a speed of 60 rpm. If the mains frequency is 50 Hz, the true speed of the gear wheel is

• A. $2940rpm$
• B. $3060rpm$
• C. $5940rpm$
• D. $5960rpm$

Answer 1

The correct option is A $2940rpm$

$\text{True speed =}(60\times 50)-60$

$\text{= 3000 - 60 = 2940 rpm}$