Upload
brianna-rogers
View
218
Download
0
Embed Size (px)
Citation preview
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.
e-e-e-
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?
Junk yard trucks
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.
e-
e- e- e- e-
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