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### Different equations

Posted: Sun Apr 15, 2018 10:29 pm
Has anyone come up with any different methods or shortcuts in determining what equations to use for different problems. There have been quite a few during the last two lectures, so I was just wondering what would be useful in remembering.

### Re: Different equations

Posted: Sun Apr 15, 2018 11:26 pm
For far for quantum, I would say that you be familiar with the following equations:
c=wavelength * frequency
E= h (constant, *6.63x10^-34) * frequency
Ephoton(hv) - Ethreshhold(phi) = Eexcess (1/2me-ve-^2)<---- heads up that is mass and velocity, mass is constant

How I am memorizing or just understanding the equations better is by thinking in terms of frequency. You can literally convert from any of these equations, just by knowing or solving for the frequency. That has really helped me in doing practice problems.

Also, make sure you understand the equations really well individually and what concepts apply to each one, because then you will know which to use, and that helps a lot when converting/moving between equations.

### Re: Different equations

Posted: Sun Apr 15, 2018 11:31 pm
I'm struggling with the same thing haha. What I do is always try to determine what the question is asking for and what is given. Then you can determine which equation(s) you can use to find your answer.
Right now the most important equations are:
Kinetic Energy: 1/2mv^2 (or Ek)= hv-work function
Planck's constant (to find energy or frequency): E= hv; with h= 6.626x10^-34
To find wavelength or frequency: wavelength x frequency(v)= speed of light(c) or 3.00 x 10^8
There's probably some I forgot as well.

### Re: Different equations

Posted: Sat Apr 21, 2018 10:28 am
What I found helpful is realizing that in certain situations, the energy of the photon (E=hv) is equivalent to the work function. Instead of trying to figure out the work function, I simply use the Einstein equation. But this is only in particular cases.

### Re: Different equations

Posted: Sun Apr 22, 2018 10:25 pm
Yea I have been having this problem as well. I find the best way is to try and quickly realize what you have, and what you are looking for. Always remember there the things we always know the constants and like the mass of an electron. So we always know some things, and then based on what is given try and use the best equation that allows us to get where we need to. Hope this helps!