Download Baby-Quiz

Baby-Quiz
1. Which of the following affects the resistance of a wire: diameter,
type of material, length, or temperature? Explain.
2. Which circuit offers the greater resistance to to battery, two bulbs
in series or two bulbs in parallel? Why?
3. If a string of five bulbs in series is added in parallel to a singlebulb circuit, you find that the brightness of the original bulb does
not change. Has the current through the battery increased,
decreased, or stayed the same? Has the resistance of the circuit
increased, decreased, or stayed the same? Explain.
4. What happens to the power supplied to a battery if the resistance
connected to the battery is doubled? Why/
Magnets and Magnetic Fields
Important: do not confuse the magnetic
poles and electric charges!
If a bar magnet is broken into two pieces,
how many magnetic poles are there?
Magnetic Field Lines
Source of Magnetism
Electric current produces a magnetic field!!!
Direction of Magnetic Field
Produced by a Current-Carrying
Wire: Right-Hand Rule
Grasp the wire with your right hand so
that your thumb points in the direction of
the conventional (positive) current; then
your fingers will encircle the wire in the
direction of the magnetic field.
Force on an Electric Current in a
Magnetic Field.
Important: the direction of the force is
always perpendicular to the direction of the
current and also perpendicular to the
direction of the magnetic field.
Another Right-Hand Rule
(for the Force)
Force on Electric Current in a
Magnetic Field
Maximum F=IlB
Units of Magnetic Field
1 Tesla (T) = 1 N/A m
1 Gauss (G) = 10-4 T
Force on an Electric Charge
Moving in a Magnetic Field
Maximum F=qvB
Right-Hand Rule Again
Important: right-hand rule defines
direction of a force acting on a
positive charge. For negatively
charged particles the force is in
exactly the opposite direction.
Don’t forget this when you are
answering questions about
electrons!!!
Proton’s Path in a Uniform
Magnetic Field
A proton travels at velocity v in a plane
perpendicular to a magnetic field. Describe
its path.
Conceptual Example: A Spiral Path
What is the path of a charged particle if its
velocity is not perpendicular to the
magnetic field?
Magnetic Field Due to a Straight
Wire
0 I
B
2 r
7
 0  4  10 T  m / A
Magnetic Field of a Solenoid
When you look down the axis of a solenoid so
that the current circulates in the
counterclockwise direction, are you looking in
the direction of the magnetic field or opposite
of it? Explain.
Force between Two Parallel
Wires
Each current produces magnetic field that is “felt” by the
other wire so that each must exert a force on the other.
Parallel current in the same directions
attract each other, antiparallel currents
repel.
Parallel current in the same directions
attract each other, antiparallel currents
repel.
An electric circuit and telephone lines.
Two wires carrying currents in opposite
direction are twisted together. How does
this reduce the magnetic fields
surrounding the wire?