Why Would I use a potential divider rather than a variable resistor?

Question

I am reading through my physics homework and this question pops up. As far I was aware it's not a either or question, I thought that variable resistors were used in the process of potential dividers? can anyone explain the answer, and not make it major complicated this isn't my strongest area :) Cheers

Answer 1

A variable resistor is commonly called a rheostat. It goes in series with a load (a car heater blower, for example) and the two together form a voltage divider. As you increase the resistance in the rheostat it has two effects: the total power used becomes less, and a larger fraction of what is used is wasted as heat in the rheostat, so the fan slows down.



A potentiometer (potential divider) is a fixed resistor with a variable center terminal, so that the voltage between one end and the center terminal is some variable fraction of that imposed across the entire resistor. Rather than being used to control power as a rheostat is, this is used to supply a defined reference voltage as input to a circuit with much higher impedance than the resistance of the potentiometer.



Email me if that doesn't make sense and we can talk more about it.

Answer 2

If you buy a variable resistor, it's called a potentiometer and has 3 terminals. So if you connect the outer terminals across an input voltage, and look at the voltage on the centre terminal, you have a potential divider. If you connect only to one outer terminal and the middle terminal, you have a variable resistor. In either case, you have a knob you can turn.



If you only need a fixed ratio, fixed resistors are cheaper and more reliable. So you can just use 2 fixed resistors in series to make a potential divider.



A potential divider gives you a stable output voltage, if the load varies but is always a much higher resistance than the divider resistors. You use a lot of power in the divider (comparitavely speaking - it might be milliwatts compared to microwatts in the load).

A series resistor only gives you a stable output voltage if the load resistance is stable. It uses less power than a potential divider (but still more than a modern switched-mode power supply, if you are trying to run a big load like a lamp and not just bias a transistor on)

Answer 3

There are many functions where a Variable resistor is also used and so on setting the attain of an amplifier,surroundings a Reference level for Temperature manipulate approach the place a specific temperature is required (commonly trim pots) making use of fixed worth resistors ordinarily will do in a circuit fixing bias level and so on but fixed values there is the main issue of tolerances in manufacture 2% 5% and so on and where a specific stage is required select on experiment is needed and in most case may also be time cosuming