Physics multiple choice question

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#1
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
The answer is A but I don't understand why.
I was thinking it was B because charge is not in either 1/2mv^2 or hc/λ
Can someone please tell my why my way of thinking is wrong and how they would come to the answer.
Thanks
0
4 years ago
#2
Think about how you can work out how much kinetic energy the electron has. 1/2mv^2 is an equation for kinetic energy, but there's a much easier way to get kinetic energy using an equation that specifically applies to accelerating through a potential difference.

After you have the energy, you're right that E=hc/λ is what you use next.
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#3
Okay I got it I'd use ev=hc/ lambda so no need for mass.
1
4 years ago
#4
(Original post by c4c4)
Okay I got it I'd use ev=hc/ lambda so no need for mass.
No problem.
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4 years ago
#5
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#6
(Original post by MagicBloo)
1st you need to draw the circuit
You then need to use the resistivity formula to find an expression for the resistance
Then use V=IR to find the current on each branch using the knowledge that the voltage across each branch is the same
Then sub into ratio formula and that's it
1
4 years ago
#7
(Original post by c4c4)

1st you need to draw the circuit
You then need to use the resistivity formula to find an expression for the resistance
Then use V=IR to find the current on each branch using the knowledge that the voltage across each branch is the same
Then sub into ratio formula and that's it
Thank you s muchh!
Trick question haha!
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#8
That's okay
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4 years ago
#9
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4 years ago
#10
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4 years ago
#11
(Original post by MagicBloo)
Do you know what the two numbers on the answers mean, eg: the 234 and 90 on answer A?

If so, think about what the nucleus is losing when it does alpha or beta emission. How does this affect the two numbers?
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