Variable Resistor Behaviour In Potential Dividers

[Porkchop]

Ok, I'm doing an electronics assignment at the moment and we'e just been getting into first order filters and the like. As a little demo/experiment thing, we were asked to measure the voltage drop across a single variable resistor being powered by a 9V DC supply. We were then told to twist it and see what happened. This resulted in a very sudden jump in the voltage read by the oscilloscope.

We then measured the voltage drop over the same variable resistor but in a potential divider circuit. On turning the dial, the rise and fall in voltage is much smoother.


Could anyone please explain the reason for this change in behaviour? Thanks in advance.

 

[jbsteele]

The reason for the difference in behavior between the two experiments is due to the fact that the potential divider circuit acts as a low pass filter, which allows only low frequency signals to pass through it. This means that any sudden changes in the voltage will be smoothed out as they pass through the circuit, resulting in a much smoother rise and fall in voltage.

 

[Moetasim]

I am happy to provide an explanation for the observed change in behavior of the variable resistor in a potential divider circuit compared to when it is used on its own.

First, it is important to understand the function of a potential divider circuit. It is used to divide the input voltage into two or more outputs, with the output voltage being dependent on the resistance values in the circuit. In this case, the variable resistor is one of the resistors in the potential divider circuit.

When the variable resistor is used on its own, twisting it causes a sudden change in its resistance. This sudden change in resistance leads to a rapid change in the voltage drop across it, resulting in the sudden jump in voltage read by the oscilloscope. This behavior is due to the fact that the voltage drop across a resistor is directly proportional to its resistance according to Ohm's law (V = IR). Therefore, a change in resistance results in a change in voltage drop.

On the other hand, when the variable resistor is used as part of a potential divider circuit, its resistance is not the only factor determining the output voltage. The output voltage is also dependent on the other resistors in the circuit and their respective values. As the variable resistor is adjusted, the change in its resistance is balanced out by the changes in the other resistors, resulting in a smoother change in the output voltage. This is because the total resistance in the circuit is changing, rather than just the resistance of one component.

In summary, the change in behavior of the variable resistor in a potential divider circuit is due to the fact that it is part of a larger circuit where its resistance is balanced out by the other components, resulting in a smoother change in the output voltage. This highlights the importance of considering the overall circuit when analyzing the behavior of individual components.