Right hand rule finding direction of magnetic force

In summary, a strong magnet placed under a horizontal conducting ring with current I creates a magnetic field at an angle θ with the vertical. The direction of the resultant magnetic force on the ring is inward and upward, perpendicular to both the current and the magnetic field. Using the right hand rule, this can be determined by curling your fingers in the direction of the current and pointing your thumb in the direction of the magnetic field. The vertical components of the magnetic force cancel out, resulting in a net downward force on the ring.
  • #1
JosephK
40
2

Homework Statement



A strong magnet is placed under a horizontal conducting ring of radius r that carries current I as shown in the figure below. The magnetic field makes an angle θ with the vertical at the ring's location.
untitled.jpg


(b) What is the direction of the resultant magnetic force on the ring?

2
to the left
to the right
upward
downward
into the screen
out of the screen


Homework Equations


Right hand rule

The Attempt at a Solution


?
 
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  • #2
What have you tried?

Where are you stuck?
 
  • #3
Crossing L and B from equation F = ILXB , where L is pointing in the same direction as current, magnetic force would point in a downward angle.

To point straight downwards the magnetic force, B has to point in a direction perpendicular to the current, although here it is pointing at an angle. So, is the B pointing not straight downwards but downwards at an angle?
 
  • #4
Umm...remember that the force is always perpendicular to both the current and the magnetic field. In the right hand rule, your thumb is the force, pointing finger is the current, and your middle finger is the field.
What are you having trouble with?
 
  • #5
Consider any small piece, ΔL, of the ring, where the direction of ΔL is the same as the direction of the current, I. Using the right hand rule for the magnetic force, ΔF = IΔL×B, the direction of which is outward and downward at an angle of θ below the horizontal.

What is the result of summing ΔF over the whole ring?
 
  • #6
amy andrews said:
Umm...remember that the force is always perpendicular to both the current and the magnetic field. In the right hand rule, your thumb is the force, pointing finger is the current, and your middle finger is the field.
What are you having trouble with?

The curvy B field throws me off.
 
  • #7
At the points where the B field intersects the ring, B is at an angle θ from the vertical, pointing outward from the ring (as well as upward).

Consider two small pieces of the ring located directly opposite each other, (ΔL)1 & (ΔL)2. Now take the magnetic force on each and add these forces. The vertical components add (they're both downward) and the horizontal components cancel.

What does that tell you about the net magnetic force on the ring?
 
  • #8
The magnetic force is downward.

Untitled-1.jpg


This is how I curl my fingers, correct?
 
  • #9
Would the magnetic force point inwards and downwards or outwards and downwards?
 
  • #10
Last edited by a moderator:
  • #11
Thank you
 

Related to Right hand rule finding direction of magnetic force

What is the right hand rule for finding the direction of magnetic force?

The right hand rule is a method used to determine the direction of the magnetic force on a charged particle moving through a magnetic field. It states that if you point your right thumb in the direction of the particle's velocity and your fingers in the direction of the magnetic field, then the direction of the magnetic force will be perpendicular to both your thumb and fingers, pointing either towards or away from your palm depending on the charge of the particle.

Why is the right hand rule important in magnetism?

The right hand rule is important in magnetism because it allows us to predict and understand the direction of the magnetic force on a charged particle. This is crucial in many real-world applications, such as designing motors and generators, as well as in understanding the behavior of charged particles in magnetic fields.

What is the difference between the right hand rule and the left hand rule in magnetism?

The right hand rule and the left hand rule are two different methods used to determine the direction of the magnetic force on a charged particle. The main difference between them is the orientation of the hand used. In the right hand rule, the right hand is used, while in the left hand rule, the left hand is used. The right hand rule is more commonly used, but both methods follow the same principle.

Can the right hand rule be used for any type of magnetic field?

Yes, the right hand rule can be used for any type of magnetic field, whether it is a uniform field or a non-uniform field. As long as you know the direction of the particle's velocity and the direction of the magnetic field, you can use the right hand rule to determine the direction of the magnetic force.

Are there any exceptions or limitations to the right hand rule?

Yes, there are some exceptions and limitations to the right hand rule. It only applies to charged particles moving through a magnetic field, and it does not work for stationary charges. Additionally, the right hand rule does not take into account the strength of the magnetic field, only the direction. In some cases, the direction of the magnetic force may not be easily determined using the right hand rule, and more advanced methods may be necessary.

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