Electric potential question (check my work)

AI Thread Summary
The discussion centers on calculating the velocity of electrons in a beam directed at a copper sphere and determining the charge required to repel the electrons. The user attempts to solve for velocity using the equation 1/2mv^2 = -qΔV but arrives at an implausibly high speed of 2.19 x 10^33 m/s, which exceeds the speed of light. Participants point out that this result is incorrect and highlight the need for a proper approach to the calculations. The user expresses uncertainty about how to proceed with the second part of the problem regarding the charge on the sphere. Clarification and guidance on both parts of the question are requested.
AnthroMecha
Messages
26
Reaction score
0

Homework Statement



A beam of electrons with energy 1.20 keV (per electron) is directed towards a solid copper sphere of radius 1.25cm.
a) Determine the velocity of the electrons in the beam.
b) The beam continues to send electrons into the sphere until it is charged up enough to repel the electrons. What is the charge on the sphere at which it stops further electrons from hitting it?

Homework Equations



1/2mv^2=-qΔV
mass of an electron=9.12X10^-31kg
elementary charge=1.602X10^-19 C

The Attempt at a Solution



Not sure if I'm going part a right:
.5(9.12X10^-31kg)v=(-1.602X10^-19 C)(1.2KeV)

Solving for v (velocity) I get 2.19 X 10^33 m/s

Does this look right?

Not even sure what to do to answer part b.

Any help is appreciated!
 
Physics news on Phys.org
Sorry, I have no time to check it fully, but 10^33 if way to much for a speed. It's 10^25 times higher than the speed of light!
 
Innoko said:
Sorry, I have no time to check it fully, but 10^33 if way to much for a speed. It's 10^25 times higher than the speed of light!

Yeah, I knew that answer sounded ridiculous.
 

Thread 'Rolling without slipping on a curved surface'

Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
View full post »

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »

Similar threads

Why Is Work Positive When Done Against the Electric Field?
Replies
22
Views
3K
Electron brought to rest by the E-field, potential difference question
Replies
4
Views
6K
Charge on a grounded conducting sphere in a uniform electric field, after ungrounding and movement
Replies
1
Views
1K
Electric field between two parallel plates
2
Replies
58
Views
5K
Potential difference between two points in an electric field
Replies
1
Views
2K
Poisson's equation: Calculating the Laplacian of an electric potential
Replies
3
Views
1K
Kinetic and potential energy of a particle attracted by charged sphere
Replies
6
Views
2K
Conceptual Issue RE: electric potential difference
Replies
1
Views
1K
How electric potential boundary condition works
Replies
5
Views
3K
Electrical Potential Energy and Potential
Replies
2
Views
2K

Hot Threads

Recent Insights

Back
Top