Using kg in DeBroglie Equation instead of g


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Connie Liang 3L
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Using kg in DeBroglie Equation instead of g

Postby Connie Liang 3L » Sun Oct 25, 2020 2:06 pm

Does anyone happen to know why we use kg as the convention for mass in the DeBroglie Equation rather than grams?

Leo Naylor 2F
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Re: Using kg in DeBroglie Equation instead of g

Postby Leo Naylor 2F » Sun Oct 25, 2020 2:07 pm

Kg is the SI unit for mass, just as, for example, meters is the SI unit for distance and seconds is the SI unit for time. Mass is sort of unusual as it is one of the only SI units with a prefix. In fact, it might actually be the only SI unit with a prefix, but I'm not sure.

Silvi_Lybbert_3A
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Re: Using kg in DeBroglie Equation instead of g

Postby Silvi_Lybbert_3A » Sun Oct 25, 2020 2:16 pm

Adding on to the reply above, because kg is the SI unit for mass, it is a part of the units for the constants. Plank's constant has units of J*s, and a joule is kg*m^2*s^-2. Because the units of Plank's constant incorporate kg, it is needed that the mass in de Broglie's equation is measured in kg so the units can cancel in the equation wavelength= h/mv and we end up with an answer in meters.

Keshav Patel 14B 2B
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Re: Using kg in DeBroglie Equation instead of g

Postby Keshav Patel 14B 2B » Sun Oct 25, 2020 2:40 pm

Planck's constant which is 6.626 times ten to the negative thirty fourth power has Joules. To cancel the joules, which is kilogram times m2 and s-2. This Kg needs to be removed to find the final frequency. You can only do this by having Kg at the denominator.


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