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Today: Oscilloscope and
Faraday’s Law
A device for displaying electronic signals.
Something else must generate the signal.
Think of it as electronic graph paper.
Oscilloscope Display
The vertical axis shows the voltage for the signal (measured in V).
The horizontal axis shows time (measured in s, ms, µs, ns).
Using an Oscilloscope
• You can measure the
amplitude of a signal as
well as the period and
• You can also change the
way the signal is
displayed by switching
the vertical (amplitude) or
horizontal (time) scales.
Faraday’s Law
Last week we put a voltage on a coil of
wire. The resulting current in the coil made
it act like a magnet. In other words a
current can produce an magnetic field –
evidence that electricity and magnetism are
Q. Can a magnetic field produce a current?
A. Yes… but it is not as easy. A constant
magnetic field cannot produce a current (or
voltage). A changing magnetic field will do
the trick.
Faraday’s law determines that the induced
current flows in a way to oppose the
change in magnetic field.
Faraday’s Law
I push the magnet
into the coil – it
pushes back on
I pull the magnet
out of the coil – it
pulls back on me.
Eddy currents
Suppose I have a pendulum with
a copper plate on the end that
swings through a magnetic field
Do I expect anything to happen?
Æ There’s a change in the
amount of magnetic field
through the copper as it
swings into the magnetic field,
so an current will be induced
Æ Eddy currents
You’ll do your own eddy current
demo with a copper tube.