Ohm's law

[chazp]

Hey folks, I am a student and am having a hard time figuring out the right procedure to find the RT & IT of a parrell circit with 35 volts and 7 20 ohm resisters. any help would be greatly appreciated!! Thanks!Ω

 

[william1]

Since in a parallel circuit the voltage on each resistor is the same, you have a current of 35V divided by 20ohms in each resistor (=1,75A). The total current is the sum of all currents = 7 times 1,75A = 12,25A.
Total resistance equals 20 divided by 7 = 2,86 ohms.

 

[cowboybob]

Keep in mind, chazp, that this method of deduction ("procedure") only works if all the resistors in the parallel circuit are of thesame identical value.

 

[DerStrom8]

Post removed. Misunderstood the question

 

[KeepItSimpleStupid]

Nice trick. The formula 1/Rt=1/R1+1/R2+...1/Rn will work for all resistors to find the equivalent resistance.

It might me instructive to use Kirkoff's law to do the problem too. Each resistor gets a value such as R1, R2 and assign a loop current Ia, Ib, Ic etc. You will then see a simplification when you set R1 to R7 equal to each other. You'll get equations like 35=(Ia-Ib)R1 and one of the form 35=IxRx

The equations for voltage and current dividers and formulas for resistances and capacitors in series and parallel are useful.

It's also instructive to note that 2 resistors of the same value in parallel is half the value. So, 8 ohms in parallel with 8 ohms is 4 ohms. It's also instructive to note that the value of a parallel combination of resistors is ALWAYS less than the lowest value resistor.

If you can download LTSPICE from Linear.com and simulate the simple circuit. This is a way of checking your answers as well. Use probes and meters to measure what you need to know.

You'll be way ahead of everybody.

 

[chazp]

Thanks guys your very helpfull!!