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### Calculating the wavelength of light

Posted: Tue Oct 10, 2017 7:56 pm
Exactly when do you use the equation E= hc/ lambda (wavelength) ?

### Re: Calculating the wavelength of light

Posted: Tue Oct 10, 2017 8:08 pm
This equation is used to calculate the energy of a photon when you are given the wavelength of the light. For example, you could use this equation on homework question 1.9 where you are given the wavelength 2.5 nm and asked for the frequency and energy of the photon.

### Re: Calculating the wavelength of light  [ENDORSED]

Posted: Tue Oct 10, 2017 8:47 pm
When calculating wavelength of light you actually use E=hc/v, where h is Planck's constant, c is the speed of light, and v is the frequency that you are given. You would not use E=hc/lambda because lambda is the wavelength of light, thus you would not need to calculate it.

When using the first equation, it is relatively simple - just plug in the value of frequency that you are given. If you are not given a frequency, you probably need to solve for it some other way and then find the value of lambda. If you cannot, then it will be impossible to find the wavelength of light.

Hope this helps!

### Re: Calculating the wavelength of light

Posted: Wed Oct 11, 2017 2:29 pm
First, you should remember the formula E=hv, where v stands for frequency and h is a constant number. Also, we know that ν = c/λ. If you plug ν = c/λ into the equation E=hv, you'll get E=hc/λ. In some questions they only give you the wavelength instead of the frequency, that's when you can apply this formula.

### Re: Calculating the wavelength of light

Posted: Wed Oct 11, 2017 10:15 pm
Since both h and c are constants, you can use the equation to either find E, energy or lambda, wavelength.
-Wenxin Fan 1H

### Re: Calculating the wavelength of light

Posted: Wed Oct 11, 2017 10:21 pm
This equation is just a combination of the equations: E=hv and c= λv. When asked for the wavelength and given the energy or asked for the energy and given the wavelength, this equation is just quicker than using the two equations above.