General Physics Lab Department of PHYSICS YONSEI University

Lab Manual (Lite)

Electromagnetic Induction Ver.20181029

Electromagnetic Induction

Experiment 1: Electromagnetic Induction I (1) Set up your equipment. Mount the coil of 𝑁𝑁 = 1600 on the tube clamp.

Position the photogate and the tube as below so that the

magnet can block infrared beam of the photogate when the magnet passes through the transparent plastic tube.

The number of turns and the direction of the windings are

indicated on the coil assembly.

(2) Run Capstone software. (2-1) Add sensors. Click the ports which you plugged the sensors into and se-

lect [Photogate] or [Voltage Sensor] from the list.

NOTICE This LITE version of manual includes only experimental procedures for easier reading on your smartphone. For more information and full instructions of the experiment, see the FULL version of manual.

Procedure

Caution The bar magnet will be dropped through the tube. Place

the cushioned basket under the tube. Make sure the magnet does not strike the table without cushion, or it may break.

(2-2) Create a timer for the photogate. Create a timer to configure automatic recording conditions. (The photogate works as an optical switch which generates an electrical signal when the magnet passes through it.) Click [Timer Setup] in the [Tools] palette and follow the steps

below to create a timer. Check [State] at step ④. [State] outputs the value of state of the photogate. The photogate generates ‘1’ while it is blocked, and ‘0’ while open. Skip steps ⑤ to ⑥ and finish the timer setup.

(2-3) Configure automatic recording conditions. We will start recording data automatically when a certain condition is achieved. Click [Recording Conditions] in the [Controls] palette.

Measurement will be started automatically at the very mo-

ment the photogate is blocked (the state of the photogate becomes ‘1’). Set the parameters of [Start Condition] as be-low. [Condition Type] : Measurement Based [Data Source] : State() [Condition] : Is Above [Value] : 0.5 Measurement will be continued only for 0.5 seconds. Set the

parameters of [Stop Condition] as below. (You can change the record time if required.) [Condition Type] : Time Based [Record Time] : 0.500 s

(2-4) Confirm the automatic recording configuration. You can see the [Record] button at the beginning.

If you click [Record], the program will waits until the start condition is achieved. ([Record] toggles to [Stop] and record-ing status display under the timer indicates [Waiting].) Even if the timer is ticking, no data is recorded.

If you block the photogate (start condition) using your finger, data recording will start automatically. The recording status display indicates [Recording].

Data recording will end automatically after 0.5 seconds (stop condition).

(2-5) Adjust the sample rate of measurements. Select [10.00 kHz] for voltage sensor in the [Controls] palette.

(2-6) Create a graph display. Click and drag the [Graph] icon from the [Displays] palette

into the workbook page. Select [Time(s)] for the 𝑥𝑥-axis and [Voltage(V)] of the voltage sensor for the 𝑦𝑦-axis.

(3) Begin recording measurements. When the magnet is passed through the coil, there is a changing magnetic flux, which induces an emf in the coil. We use the voltage sensor to measure the voltage induced in the coil as the bar magnet moves through the coil. Click [Record], and drop the magnet through the tube. Make sure the magnet blocks the infrared beam of the photogate when it passes through the photogate.

(4) Analyze your graph. [Scale axes …] rescales the graph automatically.

You can also scale or pan the graph manually.

[Select range …] selects the data range of interest.

[Display area …] measures the area between the curve and 𝑥𝑥-axis.

You can see more precise value of the area by converting the unit of measurement.

[Show coordinates …] shows the coordinate of each data point in the plot.

[…viewing of multiple runs | Select …] or [▼] activates plot-ting multiple runs together, or changes visible run.

You can change the name of each run as follows.

(5) Analyze your results. Measure the areas of each peak, and the values of maxi-mum and minimum points of the curve. Suppose the magnetic field lines of the magnet have perfect symmetry and the magnet passes a single turn of wire loop. Answer the following questions.

ℰ = −𝑑𝑑Φ𝐵𝐵

𝑑𝑑𝑑𝑑 (4)

Q What is the physical meaning of the ‘area’ under the curve?

A

Q Where is the position of the magnet when the sign of voltage changes? Explain why.

A

Q Compare the areas of each peak and explain the reason of the result.

A

Q What is the physical meaning of the maximum and mini-mum values of the curve? Compare the absolute values of them. If there is any difference between them, explain why.

A

Note We can create a graph of area under the curve as a

function of time, as follows. ① Click [Calculator] in the [Tools] palette, and define

the equation as below. (Refer to the instructions of the program for defining functions.)

Experiment 2: Electromagnetic Induction II Repeat the experiment with the magnet reversed. - Direction of poles : reversed - Turns of coil : same as 1st experiment (𝑁𝑁 = 1600) - Drop height : same as 1st experiment

Q How does the graph change? Explain the reason of the result.

A

② Create a graph display and add a new plot area with shared 𝑥𝑥-axis.

③ Choose [Time(s)] for 𝑥𝑥-axis, and [Voltage(V)] and [Φ (user defined data)] for 𝑦𝑦-axes.

The lower (green) graph is a qualitative depiction of

magnetic flux as a function of time. We can understand the relation between the change of magnetic flux and the induced emf from the graphs. Refer to the Faraday’s law of induction.

Experiment 3: Electromagnetic Induction III Repeat the experiment with varying the dropping height of

the magnet. - Direction of poles : same as 1st experiment - Turns of coil : same as 1st experiment (𝑁𝑁 = 1600) - Drop height : higher than 1st experiment

Q How does the graph change if you drop the magnet from a larger height? Is the peak of the graph higher or smaller; wider or narrower? Explain the reason of the result.

A

Experiment 4: Electromagnetic Induction IV Repeat the experiment using different turns of coils. - Direction of poles : same as 1st experiment - Turns of coils : 𝑁𝑁 = 200, 400, 800, 1600, 3200 - Drop height : same as 1st experiment

Q Express the relation between the turns of coil and the induced emf. Explain the reason of the result.

A

Experiment 5. Transformer (1) Build a transformer and connect the cables. Primary: 𝑁𝑁 = 400 Secondary: 𝑁𝑁 = 200

(2) Set up the Capstone program. (2-1) Add sensors. Click the ports which you plugged the Voltage Sensor or

patch cords into and select [Voltage Sensor] or [Output Volt-age Current Sensor] from the list.

(2-2) Configure the signal generator. [Signal Generator] [850 Output 1] [Waveform] : Sine [Frequency] : 50 Hz [Amplitude] : 1 V

[Auto] (starts or stops the generator automatically.)

Caution To avoid scratching or stabbing the coils, handle them

with care and keep them in the storage box when not in use.

(2-3) Create a scope. Click and drag the [Scope] icon from the [Displays] palette

into the workbook page.

Add independent 𝑦𝑦-axis on the right side of the graph by

clicking [Add new 𝑦𝑦-axis…].

𝑥𝑥-axis: Time(s) 𝑦𝑦-axis(left): Output Voltage, Ch 01 (V)

(signal generator output, or primary input) 𝑦𝑦-axis(right): Voltage, Ch A (V)

(voltage sensor, or secondary output)

(2-4) Select [Fast Monitor Mode] in the controls palette. [Fast Monitor Mode] displays data without recording. Check that [Recode] button is changed to [Monitor] button.

(3) Start monitoring data. (3-1) Click [Monitor] in the controls palette. (3-2) Click [Activate … trigger] in the toolbar to horizontally align repetitions of the signal.

(3-3) Scale the display

(3-4) Find the axis of each trace. Color in legend matches plot color. [Vo]: Output Voltage, Ch 01 (V) (left 𝑦𝑦-axis) (primary input) [V]: Voltage, Ch A (right 𝑦𝑦-axis) (secondary output)

(3-5) Measure the amplitudes. Click [Show data coordinates…] and read off the peak of each trace.

(4) Analyze your results. Compare the ratio of 𝑉𝑉2 to 𝑉𝑉1 with the ratio of 𝑁𝑁2 to 𝑁𝑁1 and verify the equation (8).

𝑉𝑉2𝑉𝑉1

=𝑁𝑁2𝑁𝑁1

(8)

(5) Repeat your experiment. Repeat measurement for other combinations of coils. Primary: 𝑁𝑁1 = 400 Secondary: 𝑁𝑁2 = 200, 400, 800, 1600, 3200

𝑁𝑁1 𝑁𝑁2 𝑁𝑁2 𝑁𝑁1⁄ 𝑉𝑉1 𝑉𝑉2 𝑉𝑉2 𝑉𝑉1⁄

1

400

200 0.5

1V

2 400 1

3 800 2

4 1600 4

5 3200 8

Please put your equipment in order as shown below.

□ Delete your data files from the lab computer. □ Turn off the Computer and the Interface. □ Do not disassemble your equipment. □ When you unplug the Photogate Cable from the photo-gate, pull on its connector, not on the cable itself. This con-nector has a locking tab. Press in on the locking tab before you unplug the cable. □ Keep the Magnet in the cushioned basket. □ Keep the Transformer Set in the storage box.

End of LAB Checklist