## Using Joules

$E=hv$

Sarah Bui 2L
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

### Using Joules

When do you know to use the equivalent of Joules units (kgm^2s^-2)? Is it so that we can cancel in dimensional analysis?

Cienna Henry 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am
Been upvoted: 1 time

### Re: Using Joules

Yes, it's used to cancel units

Justin Haggard 1E
Posts: 17
Joined: Fri Sep 28, 2018 12:18 am

### Re: Using Joules

Yes, since Joules are not in SI units, it becomes hard to do dimensional analysis without the conversion. One application where you would find the conversion to be very useful would be when using the De Broglie Equation:

Wavelength= $\frac{h}{m\cdot v}$

The units would be:

Wavelength = $\frac{(J\cdot s)}{(kg)(m\cdot s^{-1})}$

Converting Joules to it's SI units would make this easier to simplify:

Wavelength = $\frac{(kg\cdot m^{2}\cdot s^{-2}\cdot s)}{(kg)(m\cdot s^{-1})}$ which, after dimensional analysis, would give you the wavelength in meters (m).