# Wave Frequency in a Medium

• I
Hi I was told by physics lecturer that both the wave speed and wave length of light changes when it enters a medium, however I questioned this stating that if both wave speed and wave length changed then frequency must also according to the formula c = fλ. He stated that "frequency is energy and energy is conserved"

I was wondering if I would be able to get a more in depth answer from someone here and correct my lecturers statement.

## Answers and Replies

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BvU
Homework Helper
2019 Award
No joy: teacher is right. You can convince yourself easily if you think of the conditions at the interface. If the one 'vibrates' at a certain frequency, then the other won't 'vibrate' at a different frequency

davenn
Gold Member
2019 Award
however I questioned this stating that if both wave speed and wave length changed then frequency must also according to the formula c = fλ.
No joy: teacher is right. You can convince yourself easily if you think of the conditions at the interface. If the one 'vibrates' at a certain frequency, then the other won't 'vibrate' at a different frequency
indeed

@Theud try rearranging your formula and fix the frequency so f = c/λ .... you can have any number of variations of c and λ and have the same frequency

Dave

Last edited:
Theudius
You mean the same frequency.

davenn
davenn