From the conventional current, we have created practical ways to find the shape and direction of a magnetic field around a straight wire and a solenoid.

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Current flows to the right (I)

2D Conventional current uses right hand rule

Magnetic Field (B)

Now, looking at a wire:

Looking at the bottom: OUTGOING current

Current flow (I)

Looking at the top: INCOMING current

Current flow (I)

Looking at the top: INCOMING current Looking at the bottom: OUTGOING current

ARROW HEAD ARROW TAIL WITH FEATHERS

1. RIGHT-HAND RULE: How to determine the magnetic fields around a straight wire

In the right hand, your fingers have roles in determining the magnetic field:

Thumb: The thumb points in the same direction as the conventional current (I).

4 fingers: The four fingers point in the direction of the magnetic field (B).

I

B

Looking at the bottom: OUTGING current

Looking at the top: INCOMING current

I I

Clockwise orientation Counter-clockwise orientation

I

Now since there are magnetic fields surrounding the wire, we can pinpoint the north and south poles.

Reminder: the magnetic fields start at the north pole and head to the south pole in a bar magnet.

Compass

Compass

B B

Please note that the magnetic fields generated by a wire are circular not elliptical.

2. RIGHT-HAND RULE: How to determine the magnetic fields around a solenoid or an electromagnet

But first: what is a solenoid?

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Components of a solenoid: a solenoid is made of an iron core wrapped in electrical wire.

Power source, e.g. battery.

Iron core.

Copper wire wrapped around the core.

- +

In the right hand, your fingers have roles in determining the magnetic field:

4 fingers: The four fingers point in the same direction as the conventional current (I).

Thumb: The thumb points in the direction of the magnetic field

(B), it points north.

In the case of a solenoid, a magnetic field is also generated.

B

I

So, here is a solenoid with an iron core wrapped in a wire. The letter I indicates the direction of the current.

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Now, lets look at the solenoids from an INGOING/OUTGOING perspective.

IB

IB

Electromagnet: So, an electromagnet is a magnet created by an electrical current passing through a solenoid. It was invented by William Sturgeon in 1823.

Direction of the Magnetic Field is always perpendicular to the current RIGHT HAND RULE

Electrical current in a

CIRCULAR WIRE Magnetic field is STRAIGHT Conventional current + to –

THUMB

Points to the north of the straight magnetic field

Thumb: Magnetic Field

FOUR FINGERS

Follows the circular wire (coil) around the core

from + to -

Four Fingers: Wire

Electrical current in a

STRAIGHT WIRE

Magnetic field is CIRCULAR

THUMB

Points along the straight wire (current) direction

from + to -

Thumb: Wire

FOUR FINGERS

Follows circular magnetic field direction from N to S

Four Fingers: Magnetic Field

Direction of the

current

Direction of the

magnetic field

N

+ _

Solenoid

Note