Question

If the wavelength of light is $4000\stackrel{\circ }{A}$, then the number of waves in 1 mm length will be

• A. $25$
• B. $0.25$
• C. $0.25\times {10}^4$
• D. $25\times {10}^4$

Answer 1

The correct option is C

$0.25\times {10}^4$

Number of waves $=\frac{{10}^{-3}}{4000\times {10}^{-10}}=0.25\times {10}^4$