Question

a laser fires at frequency of 40 hertz.. Using c=3x10 to the 8 meters per second,how far apart is each pules?

Answer 1

A laser fires at frequency of 40 hertz. Using $c = 3 \times 10$ to the 8 meters per second, how far apart is each pulse?

Distance between two adjacent pulses (look at figure):

$$d = x + \frac {l}{2} + \frac {l}{2} = x + l$$

Total length of the $N$ pulses:

$$S = N d = c t$$

where $N$ number of pulses, $c$ - speed of light, $t$ - time.

$$d = \frac {c t}{N} = \frac {c}{\frac {N}{t}} = \frac {c}{f}$$ $$d = \frac {3 * 1 0 ^ {8} m / s}{4 0 H z} = 7. 5 * 1 0 ^ {6} m$$

Answer: $d = 7.5 * 10^{6}m$