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### unit conversion hw Q 1.3

Posted: **Thu Oct 25, 2018 5:38 pm**

by **juliefilice 4A**

The question reads, "In each second, a certain lamp produces 2.4x10^21 photons with a wavelength of 633 nm. How much power (in watts) is produced as radiation at this wavelength?"

I know how to solve this problem and that you start using E=hc/lambda, but do I need to convert the wavelength to m? How do I know when to convert to SI base units before starting a problem?

### Re: unit conversion hw Q 1.3

Posted: **Thu Oct 25, 2018 5:50 pm**

by **Shash Khemka 1K**

You should generally always convert wavelength into meters when substituting into an equation. Just remember to put your answer back into the form that the question is asking for. Hope this helps!

### Re: unit conversion hw Q 1.3

Posted: **Thu Oct 25, 2018 6:35 pm**

by **MichelleRamirez_2F**

You should convert the given values to the required SI units before plugging them into the equation you are using (like e=hv etc) that way when you are solving the problem you are able to "cross out" the units that you don't need in your final answer. At the end, if they are asking for a certain SI unit you convert the solution you got to those units.

### Re: unit conversion hw Q 1.3

Posted: **Sun Oct 25, 2020 10:32 am**

by **Jade_Tai_2L**

Convert the units before computing the equation. You'll know when to convert if the constant units you're using in the equation are set, and the given numbers in the problem are different. ie: speed: m.s-1, wavelength given in problem: nm

### Re: unit conversion hw Q 1.3

Posted: **Sun Oct 25, 2020 11:59 am**

by **Sabrina Galvan 3A**

You always want to covert any units into the SI base units before beginning the problem. The only time you'd convert SI units into different units is if the problems asks for it in your final answer!

### Re: unit conversion hw Q 1.3

Posted: **Sun Oct 25, 2020 12:23 pm**

by **emmaferry2D**

I had this question earlier in the week too, and I was confused since wavelengths are given in nm on the visible light spectrum. However, in equations you mostly will have to convert the wavelength you are given to meters since some constants you use in equations are in meters. You want to be able to cancel out these units and are unable to do so if one is in meters and one is in nm. hope this helps!

### Re: unit conversion hw Q 1.3

Posted: **Sun Oct 25, 2020 3:57 pm**

by **Mingzi Yang 1E**

You should convert the wavelength to meters so units can be cancelled out in future calculations for that problem. It will be convenient if you convert all units into SI base units before starting your calculations.

### Re: unit conversion hw Q 1.3

Posted: **Sun Oct 25, 2020 11:33 pm**

by **IreneSeo3F**

I would suggest converting them to SI units so that you don't have to convert it every single time along the way. Whenever the wavelength is given in nm, I would convert it to m before using the equations like c=lambdav.