Question

A stroboscopic system is used for measuring the speed of a rotating shaft. The shaft has one target mark on it. The maximum strobe rate at which synchronism is achieved is r₁ flashes per minute. The next lower flash rate at which synchronism is achieved is r₂ flashes per minute. The speed of the shaft in rpm is-
1. \(\frac{{{r_1}{r_2}}}{{{r_1} - {r_2}}}\)
2. \(\frac{{{r_1}{r_2}}}{{{r_1} + {r_2}}}\)
3. \(\frac{{r_2^2}}{{{r_1} + {r_2}}}\)
4. \(\frac{{r_1^2}}{{{r_1} + {r_2}}}\)

Answer 1

Correct Answer - Option 1 : \(\frac{{{r_1}{r_2}}}{{{r_1} - {r_2}}}\)

The maximum strobe rate at which synchronism is achieved = r₁ flashes per minute

The next lower flash rate at which synchronism is achieved = r₂ flashes per minute

The speed of the shaft in rpm is \(\frac{{{r_1}{r_2}}}{{{r_1} - {r_2}}}\)