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Physics multiple choice 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
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
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.
Reply 2
Avatar for c4c4
c4c4
OP
8
Okay I got it I'd use ev=hc/ lambda so no need for mass.
Thanks for your help
Original post by c4c4
Okay I got it I'd use ev=hc/ lambda so no need for mass.
Thanks for your help


No problem.
Reply 4
Avatar for MagicBloo
MagicBloo
How is the answer D?
Screenshot 2017-06-03 at 2.45.23 PM.png27.7KB
Reply 5
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c4c4
OP
8
IMG_20170603_122402949.jpg
Original post by MagicBloo
How is the answer D?

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
Reply 6
Avatar for MagicBloo
MagicBloo
Original post by c4c4
IMG_20170603_122402949.jpg
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!
Reply 7
Avatar for c4c4
c4c4
OP
8
That's okay
Reply 8
Avatar for MagicBloo
MagicBloo
How is the answer B?
Screenshot 2017-06-05 at 11.16.50 AM.png24.6KB
Reply 9
Avatar for MagicBloo
MagicBloo
How is the answer A?
(edited 6 years ago)
Original post by MagicBloo
How is the answer A?


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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