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When do you assume the speed of a wave is 3*10 ^ 8

I get that we assume its 3*10^8 in air and anything with a refractive index of 1... but what about waves on a string etc. Somehow questions expect you to assume that the speed is 3*10^8 through a string or a wire. Is this a general rule?
Err never seen a question where it assumes that the speed through a string or wire is the speed of light. Can you show a screenshot of one of these questions? Only waves that should be are EM waves through a vacuum.
Original post by Someboady
I get that we assume its 3*10^8 in air and anything with a refractive index of 1... but what about waves on a string etc. Somehow questions expect you to assume that the speed is 3*10^8 through a string or a wire. Is this a general rule?


If the wave is an Electromagnetic wave then it's speed is 3x10^8 unless otherwise. A string with a speed of light seems impossible right?
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Original post by Vikingninja
Err never seen a question where it assumes that the speed through a string or wire is the speed of light. Can you show a screenshot of one of these questions? Only waves that should be are EM waves through a vacuum.


AbsolutelyPhysics4.png,
Here: from the markscheme they use the speed as 3*10^8
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Original post by SirRaza97
If the wave is an Electromagnetic wave then it's speed is 3x10^8 unless otherwise. A string with a speed of light seems impossible right?


Oh so its a general rule of thumb? Yeah it doesnt seem very practical:/ Thanks! :smile:
Original post by Someboady
AbsolutelyPhysics4.png,
Here: from the markscheme they use the speed as 3*10^8


Yeah as I said EM waves travel at the speed of light. This question states that EM radiation (aka waves) is travelling down the copper.
Original post by Someboady
Oh so its a general rule of thumb? Yeah it doesnt seem very practical:/ Thanks! :smile:


Yes the reason being because of maxwell's equation:

All electromagnetic waves travel at the speed of light. :smile: That is unless said otherwise. Light can move slower if were in denser medium but dont worry too much about that
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Original post by SirRaza97
Yes the reason being because of maxwell's equation:

All electromagnetic waves travel at the speed of light. :smile: That is unless said otherwise. Light can move slower if were in denser medium but dont worry too much about that


Ahhh thanks very much! :smile:
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Original post by Vikingninja
Yeah as I said EM waves travel at the speed of light. This question states that EM radiation (aka waves) is travelling down the copper.


Ohhh thanks that clears things up! :smile:

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