Question

Suppose a wave of visible light of wavelength equal to 555nm was traveling at a velocity of 55.5 cm/s past a point "A". How long would it take for one wavelength of the light to travel past the point "A"?

Answer 1

Answer:

The answer is "$1 \times 10^{-6}\ s$"

Explanation:

$v = velocity = 55.5 \ \frac{cm}{s} = 55.5 \times 10^{-2} \ \frac{m}{s}\\\\\lambda = wavelength = 555 \ nm = 555 \times 10^{-9}\ m\\\\\upsilon = frequency\\\\v = \lambda \upsilon \\\\\upsilon = \frac{v}{ \lambda}$

$\upsilon= 55.5 \times 10^{-2} \ \frac{m}{s} \div 555 \times 10^{-9}\ m\\\\\ \ \ \ \ = \frac{10^6}{s}$

In 1 second, $10^6$ cycles take place.

1 wavelength cycle included. Thus, $10^6$ cycles include $10^6$ wavelengths.

$10^6$ wavelengths 1 second until point A $10^6$

1 wavelength is $\frac{1}{10^6}\ sec = 10^{-6}$seconds after A.