3/20/2017
Lab 9 ­ Resonance [Stony Brook Physics Laboratory Manuals]
Stony Brook Physics Laboratory Manuals
Lab 9 - Resonance
Equipment
Oscilloscope
Function generator (with 1 Ω resistor across its output)
Solenoid coil (one having either “dark red” or “yellow” wire)
Decade resistance box
Decade capacitance box
BNC to twin-banana adapters (3 are needed)
Red and black test leads
Procedure
In this lab we will use the oscilloscope to monitor the input voltage applied to the series RLC circuit (channel 1) and to
simultaneously observe the voltage across parts of the circuit on channel 2. By triggering the scope from the channel 1 input, we can
determine the relative phase relationships of the voltages appearing across each circuit element.
Connect the circuit as shown in the figure. Adjust the resistance box R to 50Ω and the capacitance box C to 0.1 μF. Set the
oscilloscope for dual trace operation and trigger from channel 1. Be sure all vertical sensitivity and time base controls are in the
“calibrated” position. Set the oscillator for maximum amplitude 5 kHz sine waves. Now adjust the frequency of the oscillator until
the voltage across R is maximum. This is the resonance frequency.
At what frequency should the maximum occur? Use the value you obtained for L in Lab 7 with the formula,
−−
−
ω0 = √
1
LC
,
which is the resonant angular frequency [ units: inverse seconds, also written as rad/s; symbol: s−1 ]. From this f0
=
ω0
2π
.
Keeping the frequency and everything else the same, interchange the resistor and capacitor, so that channel 2 now shows the voltage
across the capacitor as shown below. You should note that interchanging the capacitor is not the same as simply moving the wires
going to channel 2 and connecting them across the capacitor. (The location of the connection to ground is important!)
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3/20/2017
Lab 9 ­ Resonance [Stony Brook Physics Laboratory Manuals]
What is the phase of the capacitor voltage relative to the input voltage at resonance? What is the amplitude of the capacitor voltage at
resonance? Is it larger than the input voltage?
Still keeping the frequency the same, interchange the capacitor and the inductor so that channel 2 of the oscilloscope now shows the
voltage across the inductor.
What is the phase of the inductor voltage relative to the input voltage at resonance? What is the phase of the inductor voltage relative
to the capacitor voltage at resonance? What is the amplitude of the inductor voltage at resonance? Is it larger than the input voltage?
Explain how it is possible for the inductor and capacitor voltages to be larger than the input voltage.
Reconnect the channel 2 lead so that the scope measures the voltage across the L-C series combination. At resonance, what is the
voltage and phase across the L-C combination relative to the input voltage?
Now reconnect the circuit as you first had it so that you are measuring the voltage across the resistor again. Measure and record the
voltage across the resistor for at least 8 frequencies above and below resonance. Use R = 50 Ω and C = 0.1 mF. Plot the voltage
across the resistor as a function of frequency (ie. plot the resonance curve). Repeat the resonance curve measurement with R = 10 Ω
and C = 0.1 μF and compare.
phy134/resonance.txt · Last modified: 2016/11/17 22:11 (external edit)
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