Summary IEB Grade 12 Electrodynamics notes

ELECTROMAGNETISM

INDUCTION OF A MAGNETIC FIELD:
*Magnetic field: a region of space around a magnet where a magnetic / fero-magnetic material will
experience a magnetic force
-When current passes through a conductor a magnetic field is induced around the wire
-If you have a conductor with current through it it becomes an electromagnet (induced temporary
magnet)


THE RIGHT HAND THUMB RULE FOR A CURRENT CARRYING WIRE:
-To determine the direction of the magnetic field in a conductor
*point the thumb of your right hand in the direction of the conventional current and your fingers will curl
in the direction of the induced magnetic field
m in to
A Am Mm
CURRENT Way
CURRENT
field
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-To determine the direction of the magnetic field around a conductor where the current is flowing into or
out of the page
*into CURRENT INTO X

*out Dtt need
CURRENT OUT

FIELD I
THE RIGHT HAND RULE FOR A SOLENOID:
*Solenoid: a coil of wire, usually in cylindrical form, that generates a magnetic field when an electric
current flows through it (The magnetic field produced by a solenoid is similar to that of a bar magnet,
with distinct north and south poles)
-When current flows in a solenoid a magnetic field is induced
*Curl your fingers in the direction of the current your thumb will point to the North pole
CURRENT




C
POLES N S
CURRENT
L
POLES
S N

, FORCE ON A CURRENT CARRYING CONDUCTOR: THE MOTOR EFFECT
*When the magnetic field around a current carrying conductor interacts with another magnetic field the
conductor will experience a force
FIELD GOES FROM N TO S
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DORIGIN OF FORCE Themagnetic


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L BETWEEN
hignefEetaiai CONDUCTOR AND
EIE.gg MAGNETIC FIELD

fir 99 d lines
ygnf.ge LENGTH of conductor m

CURRENT OUT CURRENT IN
CANCELLATION IS COMPLIMENT D
MY M
N s n s
i
LE
COMPLIMENT
CANCELLATION IS




UPWARDS FORCE DOWNWARDS FORCE

To increase force on the conductor:
• Increase length of conductor between the magnetic field (add loops) Fdl
• Increase the current in the conductor FKI
• Increase the EMF across the conductor
• Increase the strength of magnetic field FAB
• The force will be at maximum if angle = 90* Fosine
min 0
FLEMING’S LEFT HAND MOTOR RULE
-To determine direction of either the force, current or magnetic field when
a current carrying conductor is in a magnetic field
*Hold left hand with thumb, index finger and middle finger at right angles
• Thumb = direction of the force
• Index finger = direction of magnetic field
• Middle finger = direction of the current