1. The speed of light in air is essentially c. (c = 3.00x108 m/s).
What is the frequency of a 650. nm light wave in air? (v = f, 650. nm = 650.E-9 m)
If the index of refraction of water is 1.33, what is the speed of light in water? (n = c/v)
What is the wavelength of the light in water, if it had a wavelength of 650. nm in air? (v = f, use the same frequency)
4.62E14 Hz, 2.26E8 m/s, 4.89E-7 m or 489 nm

2. The speed of light in air is essentially c. (= 3.00x108 m/s).
What is the frequency of a 650. nm light wave in air? (v = f, 650. nm = 650.E-9 m)
v = f
3E8 = f(650E-9m)
f = E14 Hz ≈ 4.62E14 Hz
If the index of refraction of water is 1.33, what is the speed of light in water? (n = c/v)
n = c/v
1.33 = 3.00E8/v
v = E8 m/s ≈ 2.26E8 m/s
What is the wavelength of the light in water, if it had a wavelength of 650. nm in air? (v = f, use the same frequency)
2.2556E8 m/s = ( E14 Hz) 
 = 4.887E-7 m ≈ 4.89E-7 m = 489 nm