## Equation/Formula Clarification

$c=\lambda v$

Frenz Cabison 1B
Posts: 54
Joined: Fri Sep 29, 2017 7:07 am

### Equation/Formula Clarification

For what type of problems should I use each formula?
c = λ ν
E = h ν
Ek= 1/2 mev^2
Ek=hv- phi

Derek Waters 1A
Posts: 16
Joined: Thu Jul 13, 2017 3:00 am

### Re: Equation/Formula Clarification

For E=hv you use it when asked to find energy of a photon day a blue light photon with frequency 6.4x10^14Hz

Scott Chin_1E
Posts: 55
Joined: Sat Jul 22, 2017 3:00 am

### Re: Equation/Formula Clarification

The equation $E_{k}=hv-phi$, should be used when trying to find out the kinetic energy of an ejected electron. Also, you may rearrange the terms to solve for hv in which this would be the energy of the photon released. Notice that $E_{k}$ is also equal to $\frac{1}{2}(m_{e^{-}})(v_{e^{-}}^2)$. This means when combined, The energy of the photon (hv) minus phi (work function) is equal to the kinetic energy of the electron. This can be rewritten as $hv-phi = \frac{1}{2}(m_{e^{-}})(v_{e^{-}})^2$. This makes sense because the kinetic energy of the electron should equal the energy of the photon due to conservation of energy.

Nina Gautam 1K
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am

### Re: Equation/Formula Clarification

A condensed/combined equation relating energy and wavelength is E= hc/λ. You would use it when given the wavelength and asked to find energy or vice versa.

Sandhya Rajkumar 1C
Posts: 50
Joined: Fri Jun 23, 2017 11:40 am

### Re: Equation/Formula Clarification

You can use c = λ ν to find the wavelength when you are given the frequency, or vice versa. You can combine this formula with E = h ν to get E = hc/λ to solve for either the photon energy or the wavelength, as long as you know one of the 2 variables.