# Electrical oscillations

1. Dec 13, 2006

### fewgame

CRO is connected to the batteries, the capacitor and the inductor. actually, i am not sure what the CRO is monitoring?

also, i would like to ask if electrical oscillation can be established if the positions of the inductor and the capacitor are interchanged? why?

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2. Dec 13, 2006

### fewgame

Another question

i have 2 questions for this circuit.

1. what is the application of the parallel LC circuit in resonance?
is it used as the radio tuning circuit?

2. what is the function of the resistor?
is it used for preventing a large current flowing through the signal generator in discharging so as to let the current flow through the inductor?

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3. Dec 13, 2006

### Staff: Mentor

(phew, took me forever to figure out that CRO = cathode ray oscilloscope....)

Post #1 -- Tell us what happens when the switch is thrown from left to right. What is the initial condition of the cap voltage? What is the initial condition of the inductor current? What happens when the switch makes the right side contact?

Post #2 -- (1) I don't understand the question. LC circuits have many applications. (2) Since the signal generator output in the drawing already has a high output impedance, the 33 Ohm resistor would appear to be superflous. Can you think of any reason it is there? I suppose it could be used to monitor input current from the sig-gen maybe....

4. Dec 14, 2006

### fewgame

here is the procedure for post 1

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5. Dec 14, 2006

### Staff: Mentor

6. Dec 15, 2006

### fewgame

when the switch is thrown from left to right, the capacitor discharges, the inductor gain the energy and change the energy into magnetic engery to build up a magnitic field.
the initial voltage is 6V.
the initial inductor current is zero
when the switch makes the right side contact, the same thing happens

7. Dec 15, 2006

### Staff: Mentor

That's close to right. The L and C form a resonant "tank" circuit, and the energy oscillates back and forth between the electric field between the capacitor plates and the magnetic field stored in the inductor. The energy slowly dissipates due to the losses in the wires and in the capacitor dielectric and the inductor's magnetic material (if it has any). What do the circuit voltage and current waveforms look like while this is all happening?

8. Dec 16, 2006

### fewgame

i've done the experiment. i could see on the CRO in which the voltage oscillated and the amplitude decreased.i don't know why the voltage oscillates. the CRO was measuring both the voltages of inductor and the capcitor at the same time or what? if both the same time, then i know the reason. i just want to know whether i am correct.

9. Dec 16, 2006

### fewgame

and i have a very difficult question. can electrical oscillation be establilshed if the positions of the capacitor and the inductor are interchanged. in my experiment result, it cannot. but i don't know why.

10. Dec 16, 2006

### SGT

In your experiment, the capacitor is charged and stores energy in its electric field. When you connect the switch to the inductor, there is exchange of energy between the electric field in the capacitor and the magnetic field in the inductor. That is why the voltage oscillates.
An inductor behaves as a short circuit for DC voltage. If all elements were ideal, connecting the inductor to the voltage source would cause an infinite current through the element. With real components, the current will be limited by the output resistance of the source and by the ohmic resistance of the winding. The inductor stores energy in it's magnetic field
If you could operate the switch instantaneously, The same exchange of energies would happen with the elements interchanged. Since there is a finite time for the switching, the current drops to zero in the inductor before it is connected to the capacitor, so there is no energy exchange.

11. Dec 18, 2006

### fewgame

thank you both of you!!!! you both have been very helpful~~~

still, i don't know the function of the resistor...
is it used to discharge the capacitor before another charging process by the sig. gen. comes?

12. Dec 18, 2006

### SGT

As Berkeman said, the resistor seems to be superfluous. But if you connect your scope to its terminals, you will be able to see the current waveform.

13. Dec 18, 2006

### fewgame

i see. thank you so much!!