Answer
The frequencies of electromagnetic waves that are visible are in the range $~4.3\times 10^{14}~Hz~$ to $~7.5\times 10^{14}~Hz$
Work Step by Step
We can find the frequency of EM waves with a wavelength of $400~nm$:
$\lambda~f = c$
$f = \frac{c}{\lambda}$
$f = \frac{3.0\times 10^8~m/s}{4.0\times 10^{-7}~m}$
$f = 7.5\times 10^{14}~Hz$
We can find the frequency of EM waves with a wavelength of $700~nm$:
$\lambda~f = c$
$f = \frac{c}{\lambda}$
$f = \frac{3.0\times 10^8~m/s}{7.0\times 10^{-7}~m}$
$f = 4.3\times 10^{14}~Hz$
The frequencies of electromagnetic waves that are visible are in the range $~4.3\times 10^{14}~Hz~$ to $~7.5\times 10^{14}~Hz$
