Force on an electron in a magnetic field

In summary, the conversation discusses the calculation of the force on an electron with a given velocity in a magnetic field. The formula F=qvBsinθ is used, and the cross product is calculated to be (1.92i + 1.28j + 5.77k)10^-13 N. The question arises as to why the value is positive instead of negative, considering the charge of the electron. The expert suggests discussing this with the professor and double-checking the work.
  • #1
chopnhack
53
3

Homework Statement


What is the force on an electron with a velocity v = (2i – 3j) Mms-1 in a magnetic field B = (0.8i +
0.6j – 0.4k) T

Homework Equations


F=qvBsinθ

The Attempt at a Solution


using cross product I got: (1.92i + 1.28j + 5.77k)10^-13 N which is the listed correct answer.

My question is since this was an electron, why the value wasn't negative 1.92i, etc. Wouldn't the charge have contributed to the direction? Can someone please explain this to me?
Thanks
 
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  • #2
The sign of q in the vector qvB contributes to the sign of the cross product answer...Can you show your work including the calculation of the cross product?
 
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  • #3
berkeman said:
The sign of q in the vector qvB contributes to the sign of the cross product answer...Can you show your work including the calculation of the cross product?
sure
solution.jpg
 
  • #4
Yeah, your work and your answer with the "-" signs looks right to me. You are saying that the "+" answer is listed as the correct answer?
 
  • #5
berkeman said:
Yeah, your work and your answer with the "-" signs looks right to me. You are saying that the "+" answer is listed as the correct answer?
Yes, but the professor has been known to make mistakes.
 
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  • #6
Does he/she have office hours before this is due? Show them your work and ask politely if you've missed anything...?
 
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  • #7
berkeman said:
Does he/she have office hours before this is due? Show them your work and ask politely if you've missed anything...?
I have done just that. Hopefully I can get a clarification. It's very difficult to learn magnetism while correcting typos!
Thank you!
 
  • #8
You're welcome. Just keep doing the math, and you should be fine. :smile:
 
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1. How does a magnetic field affect the force on an electron?

When an electron moves through a magnetic field, it experiences a force perpendicular to both its velocity and the direction of the magnetic field. The direction of this force can be determined using the right-hand rule.

2. What is the equation for calculating the force on an electron in a magnetic field?

The force on an electron in a magnetic field can be calculated using the equation F = qvB, where F is the force, q is the charge of the electron, v is its velocity, and B is the strength of the magnetic field.

3. How does the direction of the force on an electron change with the direction of the magnetic field?

The direction of the force on an electron changes with the direction of the magnetic field. If the direction of the magnetic field is reversed, the direction of the force will also be reversed.

4. How does the strength of the magnetic field affect the force on an electron?

The strength of the magnetic field directly affects the force on an electron. As the strength of the magnetic field increases, the force on the electron also increases. This relationship is described by the equation F = qvB.

5. Can the force on an electron in a magnetic field be controlled?

Yes, the force on an electron in a magnetic field can be controlled by adjusting the strength or direction of the magnetic field. This is why magnetic fields are commonly used in technologies such as MRI machines and particle accelerators.

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