Magnetic Induction using DrDAQ :- Faraday's Laws
Introduction
This experiment investigates magnetic induction, as governed by Faraday's
First Law.
When the magnetic flux threading a circut is changing, an E.M.F. is
induced in the circut.
The experiment involves dropping a magnet through a coil of wire and
observing the result on a PC based oscilloscope.
Equipment Required
The apparatus pictured on the right was made by Lascells in the UK and
purchased from Technology Supplies Ltd. Apart being robust, it has the
advantage that the coil can be moved up and down the tube to investigate
the effect of how fast the magnet is moving.
Similar results were obtained from using a home made version of the
kit. The home made version consisted of 100 turns of wire wrapped around a
plastic tube.
Experiment Setup
- Mount the tube and coil vertically in a clamp and stand
- Connect the coil to the pH input of the DrDAQ using the BNC to 4mm
test lead.
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Figure 1 :- Setup of Equipment
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To perform this experiment with DrDAQ we have to use the custom ranges
feature in PicoScope. To do this a file can be installed into PicoScope or
the settings can be entered manulally. Both are explained below.
Manually configuring the pH input for this experiment
- Select File|Settings|Custom ranges
- Select Add in the custom range list
- Enter the settings as shown in the image to the right
- Use the drop down menus for channel A to select pH and the
range ±576mV
- The DrDAQ screen should now look identical to the image shown in
figure 3 below
Installing PicoScope setup files to configure the pH input for this
experiment
- Download the setup
file and save it to the PICO directory
- Start up PicoScope
- Select File|Open in the PicoScope toolbar
- In the Open file window change files of type to show
Set up file (*.PSS) in the drop down menu
- Select OK
- Again the DrDAQ screen should look identical to the sceeenshot shown
in figure 3 below.
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Figure 2: Custom range settings for the pH input
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figure 3: screen
shot of PicoScope screen after installing set up files
Carrying out the Experiment
- Drop the magnet down the tube (with the north pole facing down) and
observe the trace on the screen. Catch the magnet so it does not smash on the
floor!
- Before repeating the experiment, think about how the trace will change if
you drop the magnet with the south pole facing down - try it and see if you
are correct.
- If the apparatus allows, experiment by moving the coil up and down the
tube so the magnet travels different distances before entering the coil.
Either PicoScope rulers or automatic measurements can be used to record the
amplitudes.
Questions and Discussion of Results
Q1. Why are both negative and positive voltages generated as the
magnet passes through the coil?
Q2. Why does the width (duration) of the pulse vary as the coil is
moved up and down the tube?
Q3. What is the relationship between the speed of the magnet, as it
travels through the coil, and the amplitude of the voltage produced from the
coil?
Q4. What happens to the speed of the magnet as it passes through the
coil?
Further Study
Due to the small distance from the release point of the
magnet to the top of the coil, the pulse produced by the induced E.M.F is
asymmetric. The pulse only becomes truly symmetrical when the distance between
the coil and the release point of the magnet is large. Why is this effect seen?
Measure the distance between the magnets release point and the coil, use this
to calculate the velocity. Repeat this for different distances and plot a graph
of peak amplitude versus magnet velocity.
Use Lenz's law to explain how the polarity of the magnet affects the
direction of the induced current.
Resultat & Svar på PicoTech's hemsida
