EF 152 – Physics for Engineers
Fall, 2012
Recitation 4.5 Magnetism
Objectives:
• Make basic measurements of magnetic field
• Learn basic principles of generators
• Build a basic generator
Task 1. Magnetic Fields
Use the magnetic sensor to measure the magnetic field of the earth. ___________ Gauss
1 Tesla = 10000 Gauss
When an electric current is passed through a wire, the current creates a _____________ field.
• Coils in the wire help to focus and strengthen the magnetic field
• Measure the magnetic field inside the coil. ____________ Gauss
When a magnet is passed through a wire, it creates an ______________________.
• Try lighting a small light bulb by moving a magnet through a coil.
Generators:
How is electricity generated? Quite simply, a magnet is spun inside a coil (or a coil is spun inside a magnet).
What makes the magnet spin?
• ____________________
•
____________________
•
____________________
•
____________________
•
____________________
How is the magnetic field created in a commercial generator?
_________________________________________________
View a simulation of a generator here:
http://phet.colorado.edu/en/simulation/generator
What kind of current is it generating? _________________
What happens if you increase the number of loops? _____________________
Under ‘pickup coil,’ what happens when you move the magnet up and down? ________________
What happens when you move the magnet through the coil? ___________________
Recitation 4-5
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EF 152 – Physics for Engineers
Fall, 2012
Task 2. Building a basic motor
You should have a battery, a nail, a magnet, and a wire.
• Place the magnet on the head of the nail. This will cause
the nail itself to become magnetized.
• Hold the battery vertically with the positive end up.
• Hang the point of the nail from the negative end of the battery
(try to center it on the battery)
• Hold one end of the wire with your finger firmly over the positive
end of the battery
• Touch the other end of the wire to the edge of the magnet.
• The nail should begin to rotate.
Which direction is your nail spinning? _____________
What happens if you flip the magnet over? ______________________
What happens if you flip the battery over? _______________________
How does this work?
•
which means the force will be _______________ to both the velocity and magnetic field
•
Velocity:
o velocity of what? ____________; also called ______________
o Wire should technically be directed straight into the magnet
(instead of touched against the side), but the magnet bounces
off the tip of the wire.
•
Magnetic field will be vertical (up or down,
depending on orientation of button magnet)
•
How does the force cause rotation? _____________________
Recall a basic statics principle.
Current flows out of the + end
of the battery, through the
wire, up through the nail, and
back into the battery through
the – end. This is the velocity
vector of charge,
I
Assume magnetic field
is directed upward
Right hand rule says that
the force is applied
tangent to the magnet,
“out of the page”
Recitation 4-5
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