Left/Right hand rule....not working?

  • Thread starter righthandbusy
  • Start date
  • Tags
    hand
In summary: What is confusing is that the images in your textbook don't always match the conventions that you use in your summary.
  • #1
righthandbusy
2
0
I learned the left hand/right hand rule like this:
Hold your hand in a stop motion, put your thumb perpendicular to the rest of your fingers. Like making an L sign with your index finger and thumb, but the rest of your fingers are with your index finger.

Thumb is charge/current, direction your fingers are pointing is magnetic field, and the direction your palm is facing is magnetic force. This is what it says in my workbook.

The problem is this isn't working?? Take this for example.
http://electrical4u.com/electrical/wp-content/uploads/2013/03/dc-motor-05.jpg
I have an image exactly like this in my workbook, same directions. If I try to work this out using the hand rule, magnetic force is pointing DOWNWARDS, not upwards. I've been using this method for all of my assignment, and now I'm second guessing if all my answers are wrong. What's going on??
 
Physics news on Phys.org
  • #2
Take the right part of the loop. Thumb points towards you, fingers extend to the left, palm faces down. The force is thus downwards, which is exactly what the figure shows.

Edit: using the right hand, of course, since the current follows the regular convention and flows from + to -.
 
  • Like
Likes righthandbusy
  • #3
Hello right one, :welcome:

Funny that my right hand seems to work OK in this exercise ! Did you notice there are two magnetic force arrows drawn in the picture ?

For the one on the right I let my thumb point towards me and my index finger to the left, and sure enough F points downwards.

For the one on the left I have to have my right thumb point away from me and my index finger to the left: my hand palm points up and so does the F there.

--

My personal way to remember this is that I have the Lorentz force $$F_L=q\left ( \vec E+\vec v\times\vec B\right)$$memorized and for the cross product I turn ##\vec v## (the current) over the smallest angle towards ##\vec B##. The way the corkscrew goes is the way the vector product goes.
 
  • Like
Likes righthandbusy
  • #4
thanks for replying,

I am not sure why you use your right hand instead of your left? I learned that I should use my left hand for negative charges, and right for positive? Also, does current travel from positive to negative? Because in the image, the current is traveling from the positive end of the battery to the negative one...How do I know which way electrons are moving? The image in my textbook only shows the direction of the current, no battery.
 
  • #5
Forget about left hands. It's confusing no end.
For loose electrons you use the sign of q to invert the direction if necessary.
For current you always use your right hand. The convention is that current travels from ##+## to ##-##
What actually travels doesn't matter: the effect is the same, whether positive charge moves one way or negative charge moves the opposite way.
 
  • Like
Likes righthandbusy

Related to Left/Right hand rule....not working?

1. Why is my left/right hand rule not working?

There could be several reasons for this. One possibility is that you are not applying the rule correctly. Another possibility is that there is an error in your calculations or measurements. Additionally, there may be external factors such as electromagnetic interference that are affecting the results. It is important to carefully follow the steps of the left/right hand rule and double check your work to determine the cause of the issue.

2. Can the left/right hand rule be used for any type of problem?

The left/right hand rule is a general rule that can be applied to a variety of problems in physics and engineering. However, it may not be applicable in certain situations, such as when dealing with non-conductive materials or when using different coordinate systems. It is important to understand the limitations of the rule and when it can be properly used.

3. Are there any alternative methods to the left/right hand rule?

Yes, there are alternative methods that can be used to solve problems that typically involve the left/right hand rule. These include the right hand grip rule and the right hand screw rule. These methods may be more suitable for certain problems or may provide a different perspective on the situation.

4. How can I improve my understanding and application of the left/right hand rule?

Practicing and applying the left/right hand rule in different scenarios is the best way to improve your understanding and skills. Additionally, seeking help from a teacher or tutor can provide valuable guidance and clarification. It is also important to have a solid understanding of the underlying concepts and principles behind the rule.

5. Is the left/right hand rule used in real-world applications?

Yes, the left/right hand rule is commonly used in real-world applications such as electromagnetism, circuit design, and mechanics. It is a fundamental tool in understanding and predicting the behavior of electric and magnetic fields, as well as the motion of charged particles. Familiarity with the left/right hand rule is essential for success in these fields.

Similar threads

  • Introductory Physics Homework Help
Replies
8
Views
3K
  • Introductory Physics Homework Help
2
Replies
43
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
2K
  • Introductory Physics Homework Help
Replies
1
Views
1K
  • Introductory Physics Homework Help
2
Replies
40
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
3K
Back
Top