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Physics MCQ

Question:

An electron initially at rest is accelerated through a potential difference. It is then brought to rest in a collision, and all of its kinetic energy is converted into a single photon of electromagnetic radiation. Which one of the following quantities is not required to find a value for the wavelength of the photon?

A The mass of the electron
B The charge on the electron
C The velocity of electromagnetic waves
D The value of the potential difference

Why is the answer A?
When accelerating an object across a potential difference, the total amount of energy gained is the same for an object of a constant charge, regardless of mass.

To show this, suppose we accelerate an object of charge q q and mass m m across a P.D V V . The energy gained is q×V q\times V . As you can see, nowhere is the mass used in the equation. Furthermore λ=Ehc \lambda = \frac{E}{hc} , and as energy is not dependent on mass, neither is the wavelength.
Reply 2
Original post by MouldyVinegar
When accelerating an object across a potential difference, the total amount of energy gained is the same for an object of a constant charge, regardless of mass.

To show this, suppose we accelerate an object of charge q q and mass m m across a P.D V V . The energy gained is q×V q\times V . As you can see, nowhere is the mass used in the equation. Furthermore λ=Ehc \lambda = \frac{E}{hc} , and as energy is not dependent on mass, neither is the wavelength.

Thank you very much

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