EM.9(1) - ELECTRIC LIGHT DIMMER - RL IN SERIES

A light bulb (a flood light) is connected in series with in inductance and an AC power source. The inductance consists of a large coil with a long sliding iron core. The light blub is bring when the iron core is out of the coil. The light faints as the core is pushed inside.

EM.9(2) - LRC IN SERIES

A flood light R, a capacitance C and an inductance L are connected in series to an AC power source. In this circuit, the current depends not only on R but also on the reactance X = X_L - X_C. The inductance L has a long sliding iron core which allows one to vary L. When X_L is equal to X_C, the circuit draws the maximum current giving the brightest light in the bulb.

Using this circuit, it can be shown that the capacitance "passes" AC but the inductance "blocks" AC. Changing to a DC source, it is seen that the capacitance "blocks" DC while the inductance "passes" DC.

EM.9(3) - RESONANCE CURVE IN LRC CIRCUITS

The circuit consists of an inductance L with a sliding iron core, a variable resistance R and a variable capacitance C driven by an AC power supply. The large lecture oscilloscope is used to show the resonance curves in the series and parallel circuits.

In the LRC circuit in series, the lecture oscilloscope is connected in parallel with the caapacitance.

In the parallel circuit, C and L are conncted in parallel and in series with R and the power supply. The lecture oscilloscope is then connected in parallel with R, the variable resitance.

In the series circuit, a sharp increase in the voltage amplitude is observed, while for the parallel circuit, a sharp decrease is observed when the movement of the iron core causes the circuit to resonate.

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EM.9(4) - PHASE DIFFERENCE IN A RC CIRCUIT

The phase difference in a RC, or an RL, circuit can be shown with the following simple circuit shown in the figure. The volgate across the resistor alone shows the phase of the current through the capacitor. The volgate across both, shown in the other channel of the scope, is the volgate across the capacitor -- mostly, if R << X_C = 1/wC. These two voltages are almost 90° out of phase. Adjust the two signals to have the same amplitude, and then turn the sweep rate counter-clockwise to the XY position to display the 90° phase shift in the form of a perfect circle. Although this oscilloscope has a small screen, we can set up the camera so that the larger class can see it.