units

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Julia Lee
Posts: 80
Joined: Fri Sep 28, 2018 12:29 am

units

Postby Julia Lee » Thu Oct 18, 2018 6:37 pm

Hey guys,

I'm really confused about the units that we use in the Quantum World. So if you're given the wavelength in nm, should we convert it to meters before solving the problem? Also what are the units for Energy? I know that energy can be given as Joules, eV, cal, and Watts. So if we are given one of these units, should we convert them all to Joules before solving the problem as well?

904936893
Posts: 62
Joined: Fri Sep 28, 2018 12:29 am

Re: units

Postby 904936893 » Thu Oct 18, 2018 6:46 pm

Wavelength is measured in meters, so always convert to meters! Energy is in Joules. eV, Watts, and cal can all be converted into Joules (the conversion are in the back of the book). So yes, always convert back to meters or Joules

Julia Jones 1G
Posts: 29
Joined: Fri Sep 28, 2018 12:16 am

Re: units

Postby Julia Jones 1G » Thu Oct 18, 2018 6:57 pm

When measuring wavelength, the standard unit is meters so make sure you convert it. For energy, the standard until is Joules.

anishathomas
Posts: 35
Joined: Fri Sep 28, 2018 12:25 am

Re: units

Postby anishathomas » Thu Oct 18, 2018 7:04 pm

Unless specified always stick with meters. It's just easier in the long run especially when using a specific formula.

Saima Salam 3J
Posts: 32
Joined: Fri Sep 28, 2018 12:25 am

Re: units

Postby Saima Salam 3J » Thu Oct 18, 2018 7:27 pm

As the others have said, meters is the standard use in solving for the wavelength of the photon. When we use the formula, c is the speed of light in m/s and turning nanometer into meter cancels out the meters. Finally, to represent energy we usually write it in Joules because when we use Planck's constant it is joules/second which is the universal unit for Planck's constant so using Joules allows the units to be canceled.

Jaqueline Monreal 2L
Posts: 57
Joined: Fri Sep 28, 2018 12:28 am

Re: units

Postby Jaqueline Monreal 2L » Thu Oct 18, 2018 7:31 pm

yes to calculate wavelength you should always convert to meters to make sure youre converting correctly, and im pretty sure that most problems use joules as the unit for energy

SummerLee1F
Posts: 18
Joined: Fri Sep 28, 2018 12:16 am

Re: units

Postby SummerLee1F » Thu Oct 18, 2018 7:35 pm

One really easy way I learned to convert nanometers back to meters is to just take the sig figs and move the decimals to multiply by 10^-7. For example, 340 nanometers would be 3.40 x 10^-7m.

annabel 2A
Posts: 67
Joined: Fri Sep 28, 2018 12:18 am

Re: units

Postby annabel 2A » Thu Oct 18, 2018 11:41 pm

do we need to memorize the conversion factor between Joules and eV?

Jessica Pham_4B
Posts: 9
Joined: Wed Nov 15, 2017 3:00 am

Re: units

Postby Jessica Pham_4B » Fri Oct 19, 2018 6:28 am

I'm a little confused if you look at question 1.9 I noticed that a lot of my answers came out as meters but I all ended up having to convert it to nanometers. How do I know when I can keep it meter vs. nanometers, vs. picometer, vs etc?

Margaret Akey
Posts: 80
Joined: Fri Sep 28, 2018 12:18 am

Re: units

Postby Margaret Akey » Sat Oct 20, 2018 7:24 pm

Pretty much always convert to meters, Joules, seconds, and be wary of kg/g. (You need kg when working with joules, but with conversions to moles you need grams).

Brandon Sanchez 3J
Posts: 30
Joined: Wed Oct 03, 2018 12:16 am

Re: units

Postby Brandon Sanchez 3J » Sat Oct 20, 2018 10:34 pm

Always use meters (m) for wavelength when solving a problem. Also, the units for energy are Joules (J) and should be converted to otherwise.

Madison Gil 3D
Posts: 32
Joined: Fri Sep 28, 2018 12:23 am

Re: units

Postby Madison Gil 3D » Sun Oct 21, 2018 1:56 am

A helpful tip to also know is that kg.m^2.s^-2 is equal to 1 Joule. You can use this when using the Ek = 1/2mv^2 equation. Example 1.5 in the Chemistry Principles Textbook version 6 explains this well.

Kevin Arokiaraj 4E
Posts: 18
Joined: Wed Nov 15, 2017 3:03 am

Re: units

Postby Kevin Arokiaraj 4E » Sun Oct 21, 2018 3:08 pm

Unless otherwise stated, convert to meters and stick with joules.


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