Circuits with Series/Parallel Wiring

[r_swayze]

(a) What will the ammeter read? Report this as a positive number. (b) How much power is dissipated by one of the 10.0 Ω resistors?

I am confused about which circuits are in series or parallel wiring. I know the small 10 ohm and 10 ohm loop is parallel, and the 20 ohm to 6 ohm are parallel, correct?

So, the 10 10 ohm loop's equiv resistance = 10*10/(10+10) = 5 ohm

and the 20 6 ohm equiv resistance = 20*6/(20+6) = 4.615 ohm

Now are the two equiv resistances I calculated in series with one another?

 

[Delphi51]

The 20 and the 6 are NOT in parallel: all the current through the 20 must come through the 6, so they are somewhat in series.

At the first go, I think you ignore the meter and consider the two 10's and the 20 to be in parallel. That breaks it down to a circuit with a battery and two resistors all in series so you can easily find the potential across the 10,10,20 resistors. Then put the meter back in and find the current through the 5 ohm resistance that you already calculated.

 

[r_swayze]

but if the 20 resistor were to go out, then wouldn't there still be a path for the 6 resistor to reach the battery? I thought the definition of parallel was a junction between resistors.

 

[Delphi51]

Yes, if any of the 10, 10 or 20 resistors were to disappear, current could divert to the others. The definition of parallel is that the components are connected together at both ends. If you erase the meter, you'll see that is the case for the 10, 10 and 20. The current meter can be ignored because it is supposed to have a resistance of zero (or near enough to ignore).