dis/advantage of rheostat and p.divider

I've got a question and i can'd the answer any where in my books.
- the current flowing through a torch bulb can be controlled by a variable resistor in the circuits
- potential divider arrangement
- rheostat arrangement.
What are the disadvantages and advantages of using a potential divider arrangement and the rheostat arrangement.

Thanks.

Reply 1

Drummy

rheostat circuit
response is less linear but circuit is easier to set up.

potential divider
response is more linear (halfway is half brightness) but more time / care is needed to set up. Also more energy is wasted as heat.

Reply 2

ingenieur

A main point is that potential dividers can provide the full range of voltage, from Vmax to 0V, while rheostats will not reach 0V.

In potential dividers, the load resistance is in parallel to the second half of the variable resistor. This cause the total resistance of the circuit to be lower, and the total power to be higher. Yet, less current will pass through the load compared to the rheostat.

Reply 3

uberteknik

Hmmmmmm.

Apart from the fact that this thread is over 8 years old and the previous person who resurrected it is trying to troll and failed, it does raise a good point when answering questions of this type:

Not to miss the point of the question entirely.

Which device is better all depends on the intended application and the objectives of use or experiment.

In this case, the question states the current flowing through a light bulb is to be controlled. It does not state whether this is part of an experiment nor does it state if this is for an engineering application.

It does however state the type of light bulb used (torch bulb) so it's power and therefore the voltage or current requirements of the application needs to be estimated.

It's likely the question has no right or wrong answer but is an exercise in comparing and contrasting the relative merits and disadvantages of both.

Things to think about:

Lamp manufacturers voltage and power rating.
Range and sensitivity of the current control needed, hence resistance of the control devices to obtain the correct range of current through the lamp.
Physical composition of the resistive element in both potential divider and rheostat.
Power rating of each and hence power losses and heat dissipation requirements.
Wiring of the circuit arrangement
Physical size
Safety
Cost

(edited 7 years ago)