A Current-Carrying Wire in a Magnetic Field
Magnetic force on a wire and the operating principle of an electric motor
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World's smallest electric motor
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Electric Motor 2 kinds of magnets - permanent and electric
Are the outside magnets N, N or S, S or N, S?
N, S - creates strongest field
Show Me The Physics
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The repulsive force between the electric
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Review Identify these magnetic poles
Describe the shape of this field
South Left, North Right Field is straight in the middle and curved at the top and bottom
D) Direction of the force on a wire carrying current in a magnetic field
(Top View - Wire in a magnetic Field)
Force on wire? Into, Out of Page?
Out of Page
3rd Left Hand Rule Why Left and not right?? 1) Draw Flux lines (N to S)
2) Left Thumb - direction of current
3) Four finger tips in direction of magnetic field
4) Palm shows direction of force on conductor
Figure 2 - Force on wire? Out or In?
Out of Page
Figure 3
- Force on wire? Out or In?
In
Force on conductor maximum
when conductor placed
perpendicular to field
Direct Current Electrical Motor
Why does the light filament wiggle? Show Me
The
Physics
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. The magnetic force on a current-carrying wire in a magnetic field is zero when the wire is:
2. In the 3rd left-hand rule for a wire in a magnetic field, what does the palm show?
3. Electron current flows north in a wire. The magnetic field points east. Using the 3rd left-hand rule, the force on the wire is:
4. The outer magnets of an electric motor are arranged as N facing S. Why?
5. What causes an electric motor to spin?
A Wire in a Magnetic Field
A straight wire 0.50 m long carries a current of 3.0 A. It is placed between the poles of a magnet, perpendicular to a uniform field of 0.20 T.
What is the magnitude of the magnetic force on the wire?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. The wire is turned so it is parallel to the magnetic field. What is the force now?
C2. The current in the wire is increased to 5.0 A. Substitute numerical values into a mathematical representation that can be used to determine the new magnitude of the magnetic force on the wire. Then calculate the force.
C3. With the current directed to the right (east), the force on the wire is observed to point toward the top of the page with a magnitude of 0.30 N. The current is then reversed (directed to the left) and increased to 4.0 A. Choose the direction of the new force on the wire, and determine its magnitude.
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C4. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C5. How does an electric motor use this effect?
C6. An engineer wants a small electric motor to produce larger forces on its current loop. Identify one design change that would accomplish this, and identify one drawback of that change.