# Urgent help with physics question pleaseeeWatch

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Thread starter 9 months ago
#1
The electric potential is –1.2 *10&–4 J C–1 at a point 1.2*10^–5 m from an isolated electron. An α-particle 4 He, passes through this point.

What is the magnitude of the electric potential at the mid-point between the α-particle and the electron at this instant?

So I used v=((1.6*10^-19)*2)/(4pi*(8.85*10^-12)*(1.2*10^-5)) to calculate the electric potential - and then I added this to the electric potential given and divided by 2.. but this method is wrong - can anyone help please????
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9 months ago
#2
(Original post by MrToodles4)
The electric potential is –1.2 *10&–4 J C–1 at a point 1.2*10^–5 m from an isolated electron. An α-particle 4 He, passes through this point.

What is the magnitude of the electric potential at the mid-point between the α-particle and the electron at this instant?

So I used v=((1.6*10^-19)*2)/(4pi*(8.85*10^-12)*(1.2*10^-5)) to calculate the electric potential - and then I added this to the electric potential given and divided by 2.. but this method is wrong - can anyone help please????
V=((1.6*10^-19)*2)/(4pi*(8.85*10^-12)*(1.2*10^-5))

You did not calculate the electric potential properly because you use the wrong distance.
You are asked potential at the mid point between the α-particle and the electron.
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Thread starter 9 months ago
#3
(Original post by Eimmanuel)
V=((1.6*10^-19)*2)/(4pi*(8.85*10^-12)*(1.2*10^-5))

You did not calculate the electric potential properly because you use the wrong distance.
You are asked potential at the mid point between the α-particle and the electron.

I also tried dividing that distance in red by two and calculating - still wrong??
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9 months ago
#4
Calculate the electric potential of both the electron to the mid-point and then the electric potential of the alpha particle to the mid-point. Then add them together, I think? 2
9 months ago
#5
(Original post by MrToodles4)
I also tried dividing that distance in red by two and calculating - still wrong??
Without your actual working, I can say nothing.
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Thread starter 9 months ago
#6
(Original post by Alvie)
Calculate the electric potential of both the electron to the mid-point and then the electric potential of the alpha particle to the mid-point. Then add them together, I think? Now this was extremely helpful Thank you so much - so you just ignore the electric potential they give in the question
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9 months ago
#7
(Original post by MrToodles4)
Now this was extremely helpful Thank you so much - so you just ignore the electric potential they give in the question
Yeah, kinda... I think they gave it to you so you can work out the charge of the electron but that's already known!
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9 months ago
#8
(Original post by MrToodles4)
....... so you just ignore the electric potential they give in the question
(Original post by Alvie)
Yeah, kinda... I think they gave it to you so you can work out the charge of the electron but that's already known!
The answer can be either a yes or no depending on situation.

If the electric potential of a charged particle 1 is ϕ1 at a distance r1, then the electric potential of a charged particle 1 at ½r1 is 2ϕ1.

Then the electric potential due to a charged particle 2 at a distance ½r1 and given that the magnitude of electric charge for particle 2 is twice that of particle 1, then the electric potential of a charged particle 2 at ½r1 is 4ϕ1.

Total electric potential at ½r1 due to charged particle 1 and 2 is
2ϕ1 + 4ϕ1

As for the actual question, total electric potential will be +2ϕ1 = 2 × 1.2 × 10–4 J C–1 .
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