Name: balancing weight with magnetic force
Uploaded: 2025-05-22T09:05:51.000Z
Duration: 1 min 22 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physical Science

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.PSc.6.4

magnetic-force-on-current-carrying-wires-example

Magnetic Force On Current-Carrying Wires: Example

Consider a conductor in the XY plane carrying current to the left. The conductor consists of two straight segments with a length of L parallel to the x-axis and a semicircle with a radius of R.
If the conductor is placed in a uniform magnetic field perpendicular to the plane of the wire, pointing outward, determine the total magnetic force on the conductor.
Firstly, determine the magnetic force for the individual straight sections carrying current in the x direction.
Secondly, divide the curved segment into infinitesimal straight sections having a length of dl at an angle of theta.
The infinitesimal length and the magnetic field are perpendicular to each other, and the direction of their cross product is radially outward. So, the magnitude and components of the force on the sections can be determined.
By integrating the expression with respect to theta, the force on the whole curved conductor can be determined.
Finally, by adding the forces on all three sections, the total force on the conductor in the positive y direction can be obtained.

magnetic force on current-carrying wires: example

In a magnetic field, moving charges encounter a force. If a wire contains these moving charges, i.e., if the wire is carrying a current, then a force acts on the wire as well. Consider a pair of flexible leads holding a wire that is 40 cm long and 10 g in weight in a horizontal position. The wire is placed in a constant magnetic field of 0.40 T, as shown in Figure 1(a). Determine the magnitude and direction of the current flowing in the wire needed to remove the tension in the supporting leads.
First, to solve the problem, draw a free-body diagram of the system, as shown in Figure 1(b). Second, use the right-hand rule to determine the direction of the magnetic force acting on the wire. Finally, equate the two forces to determine the current in the wire.
<img alt="magnetic field diagram; forces on current-carrying wire; &#931;F=0; physics experiment setup" src="/files/ftp_upload/13769/13769_Figure_1.png" style="text-align: center;" data-altupdatedat="1754904545000" data-alt="Magnetic field diagram, showing wire with current I, illustrating force interactions, equations &#931;F=0." />
In a free-body diagram, the tension in the supporting leads is zero when the magnetic and gravitational forces are balanced. By using the right-hand rule, the magnetic force points up, and by equating the two forces of weight and magnetic force on the wire:
<img alt="Static equilibrium equation mg=IB; analysis of magnetic force balance." src="/files/ftp_upload/13769/13769_Equation_2.svg" style="text-align: center; height: 20px;" data-altupdatedat="1754904545000" data-alt="Balance equation mg=IB; magnetic force in physics, formula diagram for educational use." />
<img alt="Physics formula for current calculation using torque in a magnetic field, featuring I=mg/LB." src="/files/ftp_upload/13769/13769_Equation_3.svg" style="text-align: center; height: 50px;" data-altupdatedat="1754904545000" data-alt="Magnetic force equation, \( I=\frac{mg}{lB} \), current calculation; physics formula analysis." />
The current in the wire can be determined. The large magnetic field creates a significant force on a length of wire to counteract the weight of the wire.

In a magnetic field, moving charges encounter a force. If a wire contains these moving charges, i.e., if the wire is carrying a current, then a force acts ...

Education

JoVE Core

Physics

Unit 1

Magnetic Forces and Fields

KEY TERMS AND CONCEPTS

balancing weight with magnetic force

Magnetic force can balance the weight of a current-carrying wire when the wire sits in a magnetic field. Moving charges in the wire feel a force, so the wire itself can be pushed upward or downward. This example uses a flexible wire that is 40 cm long and has a mass of 10 g. It is held in a horizontal position inside a constant 0.40 T magnetic field.

The goal is to find the current needed to remove the tension in the supporting leads. To do that, a free-body diagram is drawn first. The diagram shows the forces acting on the wire. Then the right-hand rule is used to find the direction of the magnetic force on the wire.

When the tension in the leads is zero, the magnetic force and the gravitational force are balanced. The magnetic force points up, so it can counter the wire’s weight. By setting the weight equal to the magnetic force, the current in the wire can be determined. The strong magnetic field produces a large enough force on the wire to support its weight.

Balancing Weight with Magnetic Force

magnetism

Magnetic Poles and Everyday Uses

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Reading Magnetic Field Lines

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Charged Particle Paths in Magnetic Fields

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magnetic force

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Magnetic fields and moving charges create magnetic force. A moving electric charge, or a current made of many moving charges, produces a magnetic field. When another current or moving charge enters that field, it feels a magnetic force in response. At the atomic level, magnetic forces come from interactions between moving electrons in the atoms of two bodies. The strength of magnetic force depends on several factors. It increases with the size of the charge and with the strength of the...

magnetic force on a current-carrying conductor

magnetic-force-on-a-current-carrying-conductor

Current and Magnetic Field Around a Wire

A current-carrying wire creates a magnetic field around it, and moving charges feel a force in that field. Because the magnetic field produced by moving charges is proportional to current, the wire itself acts as a source of magnetic field. A compass placed near the wire shows this effect by lining up tangentially around the wire. The magnetic field around a straight wire forms concentric circular loops. The right-hand rule helps determine the direction of those loops. If the thumb points in...

Magnetic force can balance the weight of a current-carrying wire when the wire sits in a magnetic field. Moving charges in the wire feel a force, so the wire itself can be pushed upward or downward. This example uses a flexible wire that is 40 cm long and has a mass of 10 g. It is held in a horizontal position inside a constant 0.40 T magnetic field. The goal is to find the current needed to remove the tension in the supporting leads. To do that, a free-body diagram is drawn first. The diagram...

force on a current loop in a magnetic field

force-on-a-current-loop-in-a-magnetic-field

Current Loops and Torque in Motors

Current loops in a magnetic field create the torque that drives a DC motor. A DC motor converts electrical energy into mechanical work. In a motor, wire loops sit inside a magnetic field. When current flows through the loops, the magnetic field pushes on them and makes the shaft rotate. The current is reversed when the loop lines up with the magnetic field. This keeps the torque on the loop going in the same direction. A commutator and brushes handle this reversal. The commutator switches the...

torque on a current loop in a magnetic field

torque-on-a-current-loop-in-a-magnetic-field

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Electron Speed Selector in Thomson’s Tube

A velocity selector uses electric and magnetic fields to choose charged particles with one speed from a beam. Many beams from a heated cathode contain particles moving at different speeds, so this setup helps produce a uniform beam. The electric and magnetic fields are perpendicular to the particle’s motion and to each other. In this arrangement, a particle with charge q, speed v, and mass m enters from the top. The magnetic field points into the plane of the paper, and the electric field...

key terms and concepts

Find out how a current-carrying wire can be supported by a magnetic field. Use a free-body diagram and the right-hand rule to solve for current.

Balancing Weight with Magnetic Force | JoVE K12

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

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Ohio’s Learning Standards and Model Curriculum

Electricity And Magnetism

Electromagnetic interactions

Tennessee Academic Standards

High School

Energy

PHYS.PS3.9

Virginia  Standards of Learning

HIgh School

PS.9

PS.9.d

PH.7

PH.7.a

PH.7.b

Alabama Course of Study Science

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Waves and Their Applications in Technologies for Information Transfer

9-12.PS.2.3.b

Florida Department of Education

SC.912.P.10

SC.912.P.10.10

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Balancing Weight with Magnetic Force

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