Question

The wavelength range of the visible spectrum extends from violet (400 nm) to red (750 nm). Express these wavelengths in frequencies (Hz). (1nm = 10 –9 m)

Answer 1

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

Answer 2

Answer:

Explanation:

V=400cm

=400×10^–9m

R=750nm

=750×10^–9m

C=3×18^8m/s

Knew V=?

Knew R=?

=c/lamda V

=3×10^8m/s

_________

400×10^–9m

=0.0075×10^17S

=7.5×10^14

R=c/lamda R

=3×10^8m/s

______________

750×10^–9m

=0.004×10^17s

=4.0×10^14 S^–1