Physics Laboratory 2
last update: 2009. 8. 31
Exp. 6. Electromagnetic Induction
- Faraday’s Law of Electromagnetic Induction -
Purpose of Experiment
Until 19C, electric and magnetic phenomena had been studied
independently and considered as having different source. But in 1820,
Orsted discovered that wire flowing currents makes magnetic field around.
Naturally, they had interest at reverse phenomenon, Faraday discovered
that 1820. In other words, he discovered that currents flow in wire when
magnet is approached.
Faraday’ s law of electromagnetic induction says if there is change of
magnetic flux to the rate of time, electromotive force is induced in around
space with same rate and that electromotive force has direction to
suppress the change of magnetic flux. And induced electric field affects
electric force to other charges inside field, like electric field from charge.
After all, electric and magnetic field can interchange and phenomenon
what we called electric, or magnetic are included wider range of
phenomenon, electromagnetic phenomenon.
In this experiment, we will confirm the electromagnetic phenomenon by
simple course, did like Faraday, and probe a voltage difference emerged
when coil rotates in the magnetic field to comprehend electromagnetic
force quantitatively. And will know about principles of motor.
Outline of Experiment
* Direction of magnet can be adjusted two directions. To be convenient, reverse
direction means that black plane goes out, right direction means that both planes
are in the coil.
We will confirm two things in this experiment.
I.
Solenoid and linear magnet are prepared for first experiment. You should just confirm
induced currents in the solenoid varying place of solenoid and linear magnet.
II. Motor and rectangular coil, and magnet making magnetic field which pierce the rectangular
coil are prepared for second experiment. When voltage is applied on the motor,
rectangular coil rotates with corresponded angular speed. So area of coil pass by
magnetic field changes in time. So electromotive force emerges and we can measure it.
We can get result of both AC and DC mode in the second experiment.
Experimental Method
These equipments are prepared in the laboratory. (Parentheses mean the number of them.)
Solenoid(1/500)
Linear magnet(1)
DC voltage tester(1)
Faraday experiment equipment(1/300)
Belt(rubber O-ring)(1)
Source device(0~10V, 0~1A)(1)
Wire with alligatorforceps(6)
Input terminal(1)
If you need more stuff, inquire to your teaching assistant or experiment
preparation room (19-114), or prepare yourself.
Experiment I. Check the electromagnetic induce phenomenon.
(a) Put into and draw magnet at solenoid and check the induced voltage from voltage tester
connected solenoid.
(b) Check the change of induced electromotive force varying pole of magnet, approaching speed
and polarity of voltage tester.

If magnet stops and solenoid moves, what will be happen?
Experiment II. Measuring the AC voltage induced by motor.
(a) To inducing AC mode voltage you should connect experiment equipment and input terminal.
Connects red terminal in AC output with number 1 and black terminal with GND. And
connects only black terminal in DC output with GND.(In other words, two black terminal are
connected with GND)

It is possible to measure AC mode and DC mode simultaneously, but it is recommended
that measure separately.

Connecting output into 1 or 5 makes output color on the monitor different. So, if DC is
connected at 5, Connecting AC to 1 makes analyzing easier.
(b) Take the permanent magnet to the right position and give voltage from power supply.
Measure the shape and magnitude of output electromotive force.
(c) Measure change of the electromotive force adding voltage of power supply.

What is the relation between voltage of power supply and electromotive force?
(d) Take the permanent magnet to the reverse position and give voltage from power supply.
Measure the shape and magnitude of output electromotive force.
(e) Measure change of the electromotive force adding voltage of power supply.
Experiment III. Measuring the DC voltage induced by motor.
(a) To inducing DC mode voltage you should connect experiment equipment and input
terminal. Connects red terminal in DC output with number 5 and black terminal with
GND. Now, remove red terminal connected number 1. And connects only black
terminal in DC output with GND.
(b) Take the permanent magnet to the right position and give voltage from power supply.
Measure the shape and magnitude of output electromotive force.
 DDDoes induced electromotive force deserve to bel DC? How should you do to get a
more DC-like shape?
(c) Measure change of the electromotive force adding voltage of power supply.
 What is the difference with Experiment II?
(d) Take the permanent magnet to the reverse position and give voltage from power supply.
Measure the shape and magnitude of output electromotive force.
 The wave shape will have remarkable difference compared with shape from (b). (Only
absolute value) Why this special change is exist?
Measure change of the electromotive force adding voltage of power supply.
Background Theory
1. A principle of motor(Induction of AC EMF)
In fig 1.(c), magnetic flux flowing plane of loop when line is vertical with a cross section of
loop makes an angle (¥è) with magnetic field is given by;
When loop rotates at constant angular velocity w, angle (¥è) of loop when time is t is;
(2)
So electromotive force induced at loop is given by Faraday’s law;
(3)
This is AC currents with same angular velocity w. The general electromotive force of loop
when area is A, winding number is N is given by;
(4)
You can know the change of electromotive force varying voltage induce by power supply.
2. A principle of motor(Induction of DC EMF)
We consider the case what use DC motor as DC generator. In fig 2, two loops are in vertically,
so electromotive force induced by brush makes electromotive force when only high
electromotive is made. So seeing the output voltage when using this motor
It has angular frequency four times than rotating number of motor.
Average voltage is given by;
(6)
Using a period we get average voltage. It is 0.9 times of maximum voltage, 0.71 times of
minimum voltage.
Above photo is faraday instruments used in experiment. Although it has not exactly same
structure with picture 2., it can be used as expressing result of experiment applying theory 2.
Why result of DC mode evolve as absolute value of Sin function? If you look center axis
carefully you can observe the difference with AC mode. To make result more DC-like, how
change the axis?
References

Constant current(voltage) power supply

Measurement of specific heat of an object - calorimeter

Measurement of temperature by the thermocouple and the digital thermometer

Treatment of measurement data

Analysis method based on the graph

James Joule - The importance of precise measurement
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