Units


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Jaedyn_Birchmier3F
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Joined: Fri Sep 28, 2018 12:26 am

Units

Postby Jaedyn_Birchmier3F » Tue Oct 09, 2018 10:39 pm

I'm a little confused on how the units cancel out for the equation E= hv. Planck's constant is represented in J x s while frequency is represented in Hertz. How does the multiplication of Hertz with Joules and seconds end up canceling out to just have E in units of Joules?

Ashley Zhu 1A
Posts: 69
Joined: Fri Sep 28, 2018 12:16 am

Re: Units

Postby Ashley Zhu 1A » Tue Oct 09, 2018 10:49 pm

The unit "hertz" means 1/seconds, so when you multiply J x s by Hz = 1/s, the seconds cancel out and you're left with J.

tierra parker 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

Re: Units

Postby tierra parker 1J » Wed Oct 10, 2018 3:25 pm

hertz is equivalent to per second (1 s^-1) so in the equation E=hv, h has units of J x s and v has units of 1/s so when you multiply the two cancel out to get J which is the unit for energy

Madeera_Mian_3B
Posts: 30
Joined: Fri Sep 28, 2018 12:24 am

Re: Units

Postby Madeera_Mian_3B » Thu Oct 11, 2018 2:42 pm

Frequency is represented by Hz (or 1/s) when doing the calculations the h units cancel with the seconds and J is left. Which shows the units for energy is J, as said before in the other replies.

Nicolle Fernandez 1E
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Re: Units

Postby Nicolle Fernandez 1E » Thu Oct 11, 2018 2:55 pm

Since hertz is 1/second when you multiply (J x second)(1/second) the seconds cancel out which leads to J.

Minsub Lee 3E
Posts: 32
Joined: Fri Sep 28, 2018 12:25 am

Re: Units

Postby Minsub Lee 3E » Thu Oct 11, 2018 4:08 pm

I like to write it out like in dimensional analysis. It will help you follow your work, and you can clearly see what can be cancelled out. Since 1 Hertz is 1/s, if you multiply it with Jxs, the s will be cancelled out, leaving just s. I suggest writing out the units in your work for dimensional analysis throughout chemistry problems such as converting moles to grams and comparing molar ratios.


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