Download Magnetism and Electric Currents

Magnetism and Electric Currents
Magnetism and Electric Currents
• The connection between electricity and
magnetism was discovered accidentally by the
Danish scientist Hans Christian Oersted (1777–
1851) in 1820.
• Oersted was giving a science lecture when he
closed a switch and allowed a current to flow
through a wire. He noticed that a nearby
compass needle rotated rapidly when the switch
was closed.
• With that simple observation, Oersted discovered
that electric currents can create magnetic fields.
Magnetic Field Produced by an Electric
Current
• The magnetic field
"circulates" around a
wire carrying current
• The field lines are
concentric circles
around the wire
Magnetic Field Produced by an Electric
Current
• Placing several
compasses around the
wire also shows that the
field lines are circles,
but it will also show the
field’s direction.
Right Hand Rule for Magnetic Fields
• To find the direction of
the magnetic field
produced by a current,
point the thumb of the
right hand in the
direction of the current
• The fingers then curl in
the direction of the
magnetic field
Strength of the Magnetic Field
Produced by a Current
• The magnetic field produced by a current in a
wire is
– Directly proportional to the current
– Inversely proportional to the distance from the
wire.
Magnetic Field Produced by a Loop of
Wire Carrying Current
• Using the right hand
rule, the field lines
produced by a current
moving through a loop
of wire all point through
the middle of that loop
Magnetic Field Produced by a Loop of
Wire Carrying Current
• This makes the loop
behave like it was a bar
magnet
• One side of the loop
behaves like a north
magnetic pole
• The other side like a
south magnetic pole
Magnetic Field Produced by a Loop of
Wire Carrying Current
• When two loops with
the same current are
placed next to one
another, the magnetic
field is strengthened
Electromagnets
• A solenoid is a long wire
wound into many closely
spaced loops forming a coil
• When current passes
through the wound up wire,
it produces a strong
magnetic field inside of the
coil
• This is referred to as an
electromagnet because the
magnetic field only exists
when current flows through
the wire
Electromagnets and a Galvanometer
• A galvanometer consists of
a coil of wire surrounded by
magnets
• As a current passes through
the galvanometer's coil, a
magnetic field is created
• This field interacts with the
field from the magnets and
causes the coil to rotate,
which moves the needle
• Galvanometers can be used
to measure current
Electromagnets and Electric Motors
• Same basic arrangement as
a galvanometer – a coil of
wire surrounded by
magnets
• When current passes
through the wire, a
magnetic field is created
which interacts with the
magnets, causing the coil to
rotate
• If the coil is attached to an
axle, it can turn a motor and
power anything that spins