What is the Correct Way to Calculate Magnetic Force on an Electron or Proton?

In summary, the conversation discusses the calculation of the force on an electron moving through a magnetic field using the Lorentz Force equation. The correct calculation requires the use of the vector form of the equation and understanding the meaning of the negative signs in the cross product. The negative signs do not indicate subtraction, but rather follow the rule for calculating the cross product of two vectors.
  • #1
SHOORY
30
1
<Moderator's note: Moved from a technical forum and thus no template.>

So there was this question
An electron that has velocity (2*10^6 i +3*10^6 j)m/s
moves through the uniform magnetic field (0.03 i - 0.15 j) T
(a) Find the force on the electron due to the magnetic field. (b) Repeat your calculation for a proton having the same velocity.
so I used this equation
F=q(vx By + vy Bx)
By is negative so I put negative and the answer was -3.364*10^-14
but the correct answer is 6.2*10^-14 and we gut it when we use By positive
Why do we have to use it positive although it is in the negative direction?
 
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  • #2
SHOORY said:
so I used this equation
F=q(vx By + vy Bx)
check that + sign...
 
  • #3
BvU said:
check that + sign...
i am sure of it its from my school book
 
  • #4
SHOORY said:
F=q(vx By + vy Bx)
Are you familiar with the vector form of the Lorentz Force equation? That would make the signs, etc., easier to see.
 
  • #5
That + sign is wrong, irrespective of what book it is from.
 
  • #6
Chandra Prayaga said:
That + sign is wrong, irrespective of what book it is from.
why is it wrong
do you know what it means
it means the total force
 
  • #7
SHOORY said:
why is it wrong
do you know what it means
it means the total force
The total force is: ##\vec F~=~q(\vec {v}~X~\vec B)##
The cross product of ##\vec v## and ##\vec B## means that the force components are:
Fx = q(vyBz - vzBy)
Fy = q(vzBx - vxBz)
Fz = q(vxBy - vyBx)
The negative signs do not mean that you are subtracting forces. They are part of the rule for calculating the cross product of two vectors. With the negative signs present, it gives the total force.
 
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  • #8
Chandra Prayaga said:
The total force is: ##\vec F~=~q(\vec {v}~X~\vec B)##
The cross product of ##\vec v## and ##\vec B## means that the force components are:
Fx = q(vyBz - vzBy)
Fy = q(vzBx - vxBz)
Fz = q(vxBy - vyBx)
The negative signs do not mean that you are subtracting forces. They are part of the rule for calculating the cross product of two vectors. With the negative signs present, it gives the total force.
Oh my god i was wrong all along thank you
 
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1. What is magnetic force?

Magnetic force is the force exerted by a magnetic field on a charged particle or a current-carrying wire. It is a fundamental force of nature, just like gravity and electromagnetic force.

2. What is a magnetic field?

A magnetic field is an area around a magnet or a current-carrying wire where the magnetic force can be detected. It is represented by lines of force that show the direction and strength of the field.

3. How is magnetic force and field related to electricity?

Magnetic force and field are closely related to electricity through the electromagnetic force, which is one of the four fundamental forces of nature. Moving electric charges create magnetic fields, and changing magnetic fields can induce electric currents.

4. How is magnetic force and field used in everyday life?

Magnetic force and field are used in many everyday applications, such as electric motors, generators, speakers, and magnetic compasses. They are also used in medical imaging techniques like MRI and in data storage devices like hard drives.

5. How can we measure magnetic force and field?

Magnetic force can be measured using a magnetometer, while magnetic field can be measured using a gaussmeter. Both instruments use magnetic sensors to detect the strength and direction of the magnetic field at a specific location.

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