Physics 124B -
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MIRAMAR COLLEGE
PHYSICS 124B LAB REPORT
TITLE:
Electromagnetic Induction
(Lenz Law)
Name_________________________
Date __________Time___________
Partners ______________________
______________________________
______________________________
Objective: Investigation of electromagnetic induction using solenoids and magnets.
Definitions: Solenoid: A solenoid is a long coil of wire made up of many turns (see Fig 21.32). When a
current flows through a solenoid, the resulting magnetic field that is very similar to that of a bar magnet,
with a north and a south pole. The direction of the magnetic field on either side of the solenoid can be
determined with RHR-2 (try it with fig. 21.32 to verify this).
Galvanometer: This measuring device consists of a small current-carrying coil which can rotate a magnet,
a pointer and a spring. When a current goes through the coil, the magnetic field causes a torque which
causes the pointer to deflect.
Part 1 - Predictions
Draw the magnetic field associated with a bar magnet:
N
sSSSsS
S
Draw the magnetic field associated with a solenoid with the current direction shown:
Part 2: Current travel direction in the solenoid vs compass needle deflection.
Equipment: solenoid, compass, power supply, connecting wires.
The RHR-2 tells us in theory which way the magnetic field of a current-carrying solenoid should point. If
the current is clockwise (looking into one end of the solenoid), which way should the magnetic field (i.e.
compass needle) point, into or out of the solenoid? ______________________________
If the current is counterclockwise, which way should the magnetic field (i.e. compass needle) point, into
or out of the solenoid?______________________________________
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Get acquainted with your solenoid.
Note there are two terminals, one where the connected wire leaves the terminal and goes under the unit
(“the bottom terminal”) and one where the wire goes around the top (“the top terminal”). Using a
compass, investigate the area around the solenoid. Is there any magnetic field associated with the solenoid
without current flowing? Why or why not?__________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Set up a circuit with the power supply and the solenoid.
1. Orient the solenoid so the top terminal is closest to you, looking into one end of the solenoid.
2. Use a current setting of 1.0 amp, and the correct color convention (the solenoid doesn’t have a
positive/negative side, but the power supply does). With the small amount of current, the solenoid
will not be dangerous to touch when connected to the power supply.
3. Connect the solenoid to the power supply in such a way that the magnetic field points out of the
solenoid.
4. Turn on power supply and verify magnetic field direction with the compass.
5. Which solenoid terminal (top or bottom) must be connected to the positive terminal of the power
supply for the compass needle to point out of the solenoid?____________________.
6. Which way does the current flow, cw or ccw?___________________________
7. Draw a diagram of your setup, showing top terminal, bottom terminal on solenoid, how they are
connected to the power supply, the direction of the current and the direction the magnetic field lines
from the solenoid are pointing. Orient the drawing like the diagram sideways, like the one on the
previous page.
8. Repeat the setup so the compass needle points into the solenoid.
9. Which solenoid terminal (top or bottom) must be connected to the positive terminal of the power
supply for the compass needle to point out of the solenoid?____________________.
10. Which way does the current flow?___________________________
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11. Draw a diagram of your setup, showing top terminal, bottom terminal on solenoid, how they are
connected to the power supply, the direction of the current and the direction the magnetic field lines
from the solenoid are pointing. Orient the drawing like the diagram sideways.
Part 3: Current travel direction in the solenoid vs. galvanometer deflection.
Equipment: galvanometer, solenoid, connecting wires, bar magnet
If current enters at the positive (right-hand) terminal of the galvanometer, the needle will have a positive
deflection (i.e to the right). If current enters at the negative (left-hand) terminal of the galvanometer, the
needle will have a negative deflection ( to the left). Connect the top solenoid terminal to the positive
terminal of the galvanometer.
With your solenoid connections, a ccw current will make the galvanometer deflect pos/neg ___________
A cw current will make the galvanometer deflect pos/neg______________________.
Bring the bar magnet near the end of the solenoid with the top terminal. Fill in the following chart with
your results.
LEADING
POLE
N
N
N
S
S
S
B MAGNET
POINTS
TOWARDS OR
AWAY
PUSH IN
PULL OUT
STATIONARY
Φ FROM
MAGNET
INC/DEC
THROUGH COIL
GALVAN.
DEFLECTION
POS/NEG
INDUCED
CURRENT
DIRECTION
CW/CCW
B
INDUCED
BY
CURRENT
IN/OUT
STATIONARY
PUSH IN
PULL OUT
STATIONARY
PUSH IN
PULL OUT
Part 4: Analysis of Faraday’s Law and Lenz’s Law: You did 6 experiments above. For each one,
explain how it agrees with Lenz’s Law. When the magnet is stationary inside the solenoid, explain how
that case agrees with Faraday’s Law. The second one is partially done as an example (don’t skip #1).
Note: Just because the direction of the magnetic field is away from the solenoid, doesn’t mean the flux
through the coil can’t increase!
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1.
2. Pushing north pole of bar magnet into solenoid causes magnetic flux pointing towards solenoid to
increase (field lines from N pole of bar magnet point away from bar magnet and therefore into solenoid).
Induced current in solenoid must induce an opposing magnetic field out of the solenoid. The induced
current had to be ccw to do so. A ccw current would cause the galvanometer to deflect ____________,
which it did.
3.
4.
5.
6.
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