Batteries and resistance

[Squirrel]

When you have a torch turned on to full brightness, does it use the maximum energy output of the battery, or could the battery be drained in, like, 5 seconds or something if you accidentally connected it to a toaster? Same thing if you turn the torch down to half brightness ' does this start to overload the battery (make it heat up or something) or is there a resistor wasting the power inside the torch, or is the internal resistance of the battery so low that it doesn't happen'or what? Also, is a potential divider an almost completely waste-free way to vary the power sent to a motor, light or any other circuit?

[Ben C]

Dpends on the battery. An alkaline battery has a high internal resistance, so it could never empty in 5 seconds. A NiCd rechargeable could easily give out over a hundred amps when short circuited and I would not want to be standing near it! It might destroy itself before discharging though - doubt it could do so in 5 seconds. And no, a potential divider is definitely not 'waste free' ! The top resistor has to take all the current of the load and drops any excess voltage. This can be quite a lot of power and of course it is wasted as heat. A transformer is better but needs to be AC and is not very variable. Most motor controllers use pulse width modulation (PWM) - do a search!

[Ben C]

Also remember that a potential divider will not react as you might expect with a load, because the low resistance load and the second resistor, in parallel, make the equivalent of a (very low value) resistor.

[Squirrel]

Thank you. That was extremely helpful.