Question

Find the range of frequenc of light that is visisble to an average human being (400 nm < \lambda < 700 nm.)

Answer 1

Given that:
$400nm<\lambda <700nm\frac{1}{700nm}<\frac{1}{\lambda }<\frac{1}{400}nm\Rightarrow \frac{1}{7\times {10}^{-7}}<\frac{1}{\lambda }<\frac{1}{4\times {10}^{-7}}\frac{3\times {10}^8}{7\times {10}^{-7}}<\frac{c}{\lambda }<\frac{3\times {10}^8}{4\times {10}^{-7}}$
[where, c = speed of light $=3\times {10}^{8}m/s$]
$\Rightarrow 4.3\times {10}^{14}<\frac{c}{\lambda }<7.5\times {10}^{14}4.3\times {10}^{14}Hz<f<7.5\times {10}^{14}Hz$