# Thread: Compton Effect

1. photons can hit electrons as if they were particles, and we can apply conservation of energy and momentum.

incident photon---> electron at rest* ---> *splits* electron moves with momentum p', photon moves with momentum q', with angle theta between them.

electron at rest has energy E=mc^2 and no momentum.

The mathematics I've been shown makes sense, all up to one point:

using the conservation of momentum,
q = q' + p'
then they square the above term and suddenly:
p^2 = (q' - q)^2 = q'^2 + q^2 -2q' (dot product) q

Can anyone here explain how they did that?

2.

3.

4. dot product
i think its the Scalar product, not the Dot product.

or maybe this is a different one;

5. @ Magimaster:
Wow, that's awesome.
Only problem is, I can't get to the fourth step :?
I might want to revise dot products in a bit more depth...

edit: no wait, I worked it out

@ Heinsbergrelatz:
Dot product and Scalar products are exactly the same. Your equation is the same as magi's it just misses the dot on the second step and replaces q·q' with cos... etc.

6. Dot product and Scalar products are exactly the same

i see

7. Originally Posted by Futurist
@ Magimaster:
Wow, that's awesome.
Only problem is, I can't get to the fourth step :?
I might want to revise dot products in a bit more depth...
The dot product obeys the same comutative and associative properties as ordinary multiplication. That is all that is required in magimaster's calculation.

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