Units in Solving Questions regarding De Broglie Equation


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Anirudh Mahadev 1G
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Units in Solving Questions regarding De Broglie Equation

Postby Anirudh Mahadev 1G » Mon Oct 19, 2020 10:21 am

In the lecture from today, 10/19, Dr. Lavelle worked out a question where a car, weighing 1500 kg travelled at 27 m/s, and we had to find the De Broglie Wavelength. In terms of units, Planck's Constant is in Joule seconds, mass is in kilograms, and velocity is in meters per second. This question worked out fine, since all of the units are correct. If the question gave us a different mass unit, such as grams, would we have to convert the mass into kilograms to use the De Broglie Equation? If we use grams instead of kilograms for a smaller object, I think our answer for the wavelength would be a thousand times too large.

Sophia Hu 1A
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Re: Units in Solving Questions regarding De Broglie Equation

Postby Sophia Hu 1A » Mon Oct 19, 2020 10:23 am

Yes, you have to convert the mass from grams to kilograms. Joules is measured in kg m^2 s^-2. Therefore, in order for the De Broglie Equation to work you have to use a mass with kilograms in order to cancel out with the kg in Joules in Planck's Constant.

Cecilia Cisneros 1F
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Re: Units in Solving Questions regarding De Broglie Equation

Postby Cecilia Cisneros 1F » Mon Oct 19, 2020 10:26 am

Yes, you must always convert your units to match within your calculations! Therefore, in that case a mass of grams should be converted to kilograms in order to solve the problem.

Abby Lam 3F
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Re: Units in Solving Questions regarding De Broglie Equation

Postby Abby Lam 3F » Mon Oct 19, 2020 11:06 am

Yes, you should convert to kg

Pranav Daggubati 3C
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Re: Units in Solving Questions regarding De Broglie Equation

Postby Pranav Daggubati 3C » Mon Oct 19, 2020 11:09 am

If you were to use grams, you would get milliJoules instead of Joules and you would have to multiply by to get the right units in joules.


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