Question

Compare blue and red light from the visible spectrum. which has: the longer wavelength? the greater frequency? the greater energy?

Answer 1

1) By looking at the table of the visible spectrum, we see that blue light has a wavelength in the range [450-490 nm], while red light has wavelength in the range [620-750 nm]. Therefore, red light has longer wavelength than blue light.

2) The frequency f of an electromagnetic wave is related to its wavelength $\lambda$ by the formula
$f= \frac{c}{\lambda}$
where c is the speed of light. We see that the frequency is inversely proportional to the wavelength, so the shorter the wavelength, the greater the frequency. In this case, blue light has shorter wavelength than red light, so blue light has greater frequency than red light.

3) The energy of the photons of an electromagnetic wave is given by
$E=hf$
where h is the Planck constant and f is the frequency. We see that the energy is directly proportional to the frequency, so the greater the frequency, the greater the energy. In this problem, blue light has greater frequency than red light, so blue light has also greater energy than red light.