Download Magnets & Magnetic fields and forces

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts

Speed of gravity wikipedia , lookup

Condensed matter physics wikipedia , lookup

Maxwell's equations wikipedia , lookup

Electrostatics wikipedia , lookup

Field (physics) wikipedia , lookup

Neutron magnetic moment wikipedia , lookup

Magnetic field wikipedia , lookup

Electromagnetism wikipedia , lookup

Magnetic monopole wikipedia , lookup

Aharonov–Bohm effect wikipedia , lookup

Superconductivity wikipedia , lookup

Lorentz force wikipedia , lookup

Electromagnet wikipedia , lookup

Transcript
Magnetic Fields
Ch 20 is about Magnetism, magnetic
fields, and interactions between
moving charges and magnetic fields
Magnetic materials
• Magnetic materials: what are they?
• How do you make a magnet?
• What is a compass and how does it align
with a magnetic field?
• Why does a magnet “stick” to certain
metals?
Magnetism
• Magnetic fields are not electric fields
• A magnetic field does not mess with a
stationary charge, but an electric field
does.
• For every magnet, there is a North and
South pole which can never be
“separated”. Ain’t no thing as a North by
itself.
Magnetism
• Magnetic field lines point in the direction
that a north side of a magnet would align
• A North on a compass aligns itself with
magnetic field lines.
• The North pole is the south pole
• For a magnet, field lines point away from
N and into the S.
Moving charges create Bmagnetic
Fields (B fields)
• A wire carrying a current creates a circular
magnetic field around it (Use right hand rule #2
for orientation)
• RHR#2: point thumb in direction of current, the
fingers wrap in the direction of the magnetic
field.
• If you coil a wire or wrap wire around a cylinder,
the magnetic field from each wrap adds, creating
a North at one end of the cylinder and a South at
the other end. This is an electro-magnet,
sometime called a solenoid.
Force on an Electric Current (or a
moving charge) in a magnetic field
• If a charge moves across a magnetic field, it
experiences a “strange” magnetic force which is
oriented Perpendicular to its motion and the
direction of B.
• For a current in a wire, the Force = ILBsinө, I =
current, L = Length of wire crossing the magnetic
field, B = magnetic field strength (Teslas) and ө
= angle between the wire and the magnetic field
lines. Notice when the angle = 90, the Force is a
maximum.
• F = BILSinө, (force = bill(nye)Sin(guy) )
Force on a Moving charge crossing
a Magnetic Field
• The same idea applies to a charged object
crossing a magnetic field (like a charged duck
flying across the earth’s magnetic field)
• F = qvBsinө, q = charge (coulombs), v = velocity,
B = magnetic field (Tesla). Again, when the
angle = 90, the charge is crossing the magnetic
field lines and is a maximum.
• If the angle = 0, the charge is moving parallel to
the magnetic field lines and there ain’t not no
Force no mo.
Right Hand Rule #1
• For the Force on a moving charge you must use
RHR #1 to determine the direction of the force
• 1) Point fingers in direction of the moving charge
or current
• 2) Orient your Balm so it points in the direction of
the magnetic Field (B)
• 3) Extend you Fumb and it points in the direction
of the Force.
• 4) the above orientation is for a + (positive)
charge, for a – (negative) charge, the direction
of the force is opposite.
Motion of a charged particle
moving across a magnetic field
• The Force on a charge particle moving across a
uniform magnetic field is always perpendicular to
its motion.
• This force causes the particle to move in a circle
(as in circular motion, dude)
• F=qvB = ma =mv2/r which can be rearranged to
yield r = mv/qB.
• This is a fairly common equation which shows
up, it’s a derived equation and not on the green
equation sheet.
Magnetic Field Due to a Long
Straight Wire
• For a long straight wire, a circular
magnetic field exists (use RHR#2 for its
direction)
• B = (μ0I)/(2лr)
• μ= permeability of free space