Question

wavelength range of visible spectrum extends from violet 400nm to red 750nm. express these wavelengths in frequencies (Hz)

Answer 1

frequency=velocity of light*wavelength
=3×10^8×400=1200×10^8 Hz
Similarly frequency of higher wavelength=2250×10^8 Hz

Answer 2

We know that v=λf where v is velocity, λ is wavelength and f is frequency.

Range of spectrum is 400 nm to 750 nm which equals

400 nm=4×10⁻⁷ m

750 nm=7.5*10⁻⁷m

Here v=c=3*10⁸ m/s

So, Upper limit

v=λf

∴3*10⁸=4*10⁻⁷*f

∴f=3*10⁸/4*10⁻⁷

∴f=0.75*10¹⁵

So f=7.5*10¹⁴ Hz

Similarly The lower limit will be

4*10¹⁴Hz

Thus the range of spectrum in frequency is 4*10¹⁴ Hz-7.5*10¹⁴ Hz

or 400 Thz to 750 Thz