Answer
(a) $9.38\times 10^{14}Hz$ to $1.07\times 10^{15}Hz$.
(b) $UV-A$
Work Step by Step
(a) We know that
$f=\frac{c}{\lambda}$
$\implies f_1=\frac{3\times 10^8m/s}{400\times 10^{-9}m}=7.50\times 10^{14}Hz$
$f_2=\frac{3\times 10^8m/s}{320\times 10^{-9}m}=9.38\times 10^{14}Hz$
The frequency range of UV-B is:
$f_3=\frac{c}{\lambda}$
$f_3=\frac{3\times 10^8m/s}{280\times 10^{-9}m}=1.07\times 10^{15}Hz$
The frequency range of UV-c is given as
$f_4=\frac{c}{\lambda}$
We plug in the known values to obtain:
$f_4=\frac{3\times 10^8m/s}{100\times 10^{-9}m}=3.00\times 10^{15}Hz$
Thus, the range of frequencies for UV-B radiation is $9.38\times 10^{14}Hz$ to $1.07\times 10^{15}Hz$.
(b) As given that the frequency is $f=7.9\times 10^{14}Hz$. We know that this frequency is observed in the range of category $UV-A$ and it ranges from $7.50\times 10^{14}Hz$ to $9.38\times 10^{14}Hz$.
