Very fast right hand rule question

In summary, the electrons in a television tube have a kinetic energy of 2.40×10–15 J and initially move horizontally from west to east. The vertical component of the earth’s magnetic field, with a magnitude of 2.00×10–5 T, points down towards the surface of the earth. The force on the electrons is directed south, which can be determined using the right hand rule and the equation f=qv*b. It is also helpful to think in terms of vectors and cross products when understanding this concept. For more information and resources on the right hand rule, check out the provided link.
  • #1
michaelw
80
0
The electrons in the beam of a television tube have a kinetic energy of 2.40×10–15 J. Initially, the electrons move horizontally from west to east. The vertical component of the earth’s magnetic field points down, toward the surface of the earth, and has a magnitude of 2.00×10–5 T.

Just when i thought i had this right hand rule thing down, i come across this
heres what i did
used left hand, fingers down, thumb pointing right, force = out of page
yet the answer is the force is directed south??

what did i do wrong?
 
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  • #2
The charge of an electron is negative. :)
so f=qv*b. when q is negative, force is in the opposite direction.

If you ask me, instead of thinking in terms of this rule, try think in terms of vectors and cross products
 
  • #3
i have no clue how to do cross products :/ and i used left hand since its an electron :)
 
  • #4
michaelw said:
heres what i did
used left hand, fingers down, thumb pointing right, force = out of page
yet the answer is the force is directed south??

what did i do wrong?
You are just interpreting the answer incorrectly. I assume your picture (mental or otherwise) shows East as going to the right of the page, and down as going down the page? The answer, given that, is out of the page--but out of the page = South! (Always translate the answer back into the language of the question.)

Since you seem to be having quite a time with the right hand rule, check out the links I provide here: https://www.physicsforums.com/showpost.php?p=389039&postcount=8
 

1. What is the right hand rule?

The right hand rule is a technique used in physics to determine the direction of a magnetic field or current flow in a wire. It is based on the principle that the direction of the magnetic field is perpendicular to the direction of the current flow and can be determined using the right hand.

2. How do you use the right hand rule?

To use the right hand rule, extend your right hand and point your thumb in the direction of the current flow. Then curl your fingers towards the direction of the magnetic field. Your fingers will point in the direction of the magnetic field.

3. What is the difference between the left and right hand rule?

The left hand rule is used for determining the direction of force on a current-carrying wire in a magnetic field, while the right hand rule is used for determining the direction of the magnetic field or current flow. The two rules use the same hand, but for different purposes.

4. When is the right hand rule used?

The right hand rule is used in various fields of science and engineering, including electromagnetism, electronics, and mechanics. It is commonly used to solve problems related to magnetic fields and current flow, such as calculating the force on a current-carrying wire in a magnetic field.

5. Can the right hand rule be used for any type of current flow?

Yes, the right hand rule can be used for both direct current (DC) and alternating current (AC) flow. However, for AC flow, the direction of the current changes periodically, so the direction of the magnetic field also changes. In this case, the right hand rule can be used to determine the direction of the magnetic field at a specific moment in time.

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