When light travels from a medium it moves faster in (such as air) to a medium it moves slower in (such as glass) its velocity decreases. what else happens? a) the frequency increases but the wavelength remains the same. b) the wavelength increases but the frequency remains the same. c) the wavelength decreases but the frequency remains the same. d) the frequency decreases but the wavelength remains the same.

c) The wavelength decreases but the frequency remains the same.

Explanation:

Light travels at different speed in different mediums.

Refractive index is equal to velocity of the light 'c' in empty space divided by the velocity 'v' in the substance.

Or ,

n = c/v.

The frequency of the light does not change but the wavelength of the light changes with change in the speed.

c = frequency × Wavelength

Frequency is constant,

The formula can be written as:

n = λ / λn.

Where,  

λn is the wavelength in the medium

λ is the wavelength in vacuum

When the light travels to glass, it speed slows down and also the wavelength decreases as both are directly proportional. There will be no effect on frequency.