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

1. 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?
2. 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.
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?
4. (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.
Absolutely,
Here: from the markscheme they use the speed as 3*10^8
5. (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!
Absolutely,
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.
Oh so its a general rule of thumb? Yeah it doesnt seem very practical:/ Thanks!
Yes the reason being because of maxwell's equation:

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

All electromagnetic waves travel at the speed of light. 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!
9. (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!

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