Confused to the max Re-aranging equations.

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The discussion revolves around a student's confusion after manipulating equations from an AS level physics exam. They derived an equation suggesting that velocity could equal twice the speed of light, which raised questions about the validity of their substitutions. A key point made is that the equations E=hc/λ and λ=h/mv represent different concepts: the first relates to photon energy, while the second pertains to the deBroglie wavelength of a particle. The response emphasizes that substituting terms without considering their context leads to nonsensical results. Overall, the conversation highlights the importance of understanding the distinct meanings of physical equations before manipulating them.
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Okay so today i sat a AS level physics paper and after finishing the exam i looked threw the equation booklet and decided to do some manipulation and i came up with this and was wondering what you guys think of it. I am confused! :)

E=hc/λ AND λ=h/mv
subbing in gives E=hcmv/h which is E=cmv
conservation of energy...
cmv=1/2mv^2
2c=v

how can velocity = 2*speed of light?

Thoughts?
 
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slawted said:
Okay so today i sat a AS level physics paper and after finishing the exam i looked threw the equation booklet and decided to do some manipulation and i came up with this and was wondering what you guys think of it. I am confused! :)

E=hc/λ AND λ=h/mv
subbing in gives E=hcmv/h which is E=cmv
conservation of energy...
cmv=1/2mv^2
2c=v

how can velocity = 2*speed of light?

Thoughts?

Just because something has the same name or the same symbol, does not mean they are representing the SAME thing.

E=hc/\lambda is the energy per photon with that particular wavelength, whereas \lambda=h/mv is the deBroglie wavelength for a non-relativistic particle with mass m at velocity v!

You can't simply substitute apples into oranges. If you do that, you get ridiculous answer like what you got.

Zz.
 

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