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Electricity and Magnetism
 Aim: to investigate some components having Non-linear Characteristics See characteristic, resistance, internal resistance of a battery This experiment is to show how the characteristic of a component can be useful in solving some circuit calculations. There are, of course, many possible components that could be investigated but the three suggested are - a 6V filament light bulb - a voltage dependent resistor, v.d.r. (sometimes called a varistor) - a silicon diode Method In the circuit shown below, connect the component to be investigated first one way then the opposite way. Something like a 6v d.c. supply will be suitable for the bulb and diode. For the v.d.r. it will probably be necessary to increase to a higher voltage supply to show the non-linearity. Set the potential divider to give zero voltage before connecting the component into the circuit, then increase the voltage very gradually. Find out the maximum currents which can be supported by the components before making measurements. Plot your results on axes as shown below. Using the Characteristics Consider the circuit shown below, in which E = 1.1V and r = 25Ω. A diode connected as shown here is said to be forward biased. This is a simple enough circuit... try to calculate the current flowing in this circuit. It will soon become clear that you can not calculate these answers without knowing the detailed characteristics of the diode. Let us assume that the diode in this circuit is the one which you used in your experiment. If you plot the characteristics of the battery in this circuit on the same axes as the characteristics of the diode, you should see how to answer the question (see here if necessary). Using the same method, consider the following circuit, in which the bulb is the one you used in your experiment and E = 4.5V and r = 15Ω. Find the voltage across the bulb and the current flowing in the circuit.

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