Question on The "Big Rules" for Waves

[Perseverance7779311]

Hey guys, Ive been going over the two big rules for waves, but im very confused because for them to be true, how could you possibly use the equation c=lambda(v)/ v=lambda(f) to answer certain questions.

Big Rule 1: The speed of a wave is determined by the type of wave and the characteristic of the medium, not by the frequency

Big Rule 2: When a wave passes into another medium, its speed changes, but its frequency does not.

Thank you.

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[Eaglefan]

not sure what your question is, really. but this might clear it up

v=lambda*f f=v/lambda f is constant, v changes when entering a different medium (since v is dependent on medium) and v changes in response. v increases in direct proportion with wavelength. c is just speed of light waves in a vacuum; if it's not in a vacuum, the speed changes from c to something else.

 

[Perseverance7779311]

@Eaglefan ,Thank you. Let me just ask you this though, in questions where we are asked to determine the frequency, how would frequency be constant?

 

[Cawolf]

If you are asked to determine frequency, you will either be given (or be able to determine) the speed of the wave and it's wavelength. From there you can find the frequency.

If I asked you what the frequency of 600 nm light where the speed of light is 0.9c, you could figure it out using the formula you listed. The thing to see is that this light would have a different wavelength in a medium where light isn't as slow, but the frequency would be the same.

It is all just conservation of energy.

 

[Perseverance7779311]

Thank you.