# Confused to the max! Re-aranging equations.

1. Jun 9, 2010

### slawted

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. Im 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?

2. Jun 9, 2010

### ZapperZ

Staff Emeritus
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.