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MCQs: Component combinations

The internal resistace r in the following circuit is 1 Ω.

The pd from P to S is:

No current flows so pd across r is 0 V
Pd from P to S = 12 V

The current in the following circuit is 0.5 A.

The internal resistance r is:

Total resistance = V/I = 12/0.5 = 24 Ω
Internal resistance = 4 Ω

Each cell in the diagram below has an EMF = 6 V.

The current in the circuit is:

Total EMF = 6 - 6 + 6 = 6 V
I = V/R = 6/6 = 1 A

Note the following circuit.

The current is:

Total EMF = 12 +12 + 6 = 30 V
I = V/R = 30/12 = 2.5 A

Note the following combination of resistors.

The total resistance is:

The one in the middle draws no current (because there is no potential difference across it) so can be ignored.
Two 12 Ω in series = 24 Ω
Two 24 Ω in parallel = 12 Ω

Note the following combination of resistors.

The total resistance is:

R = 12 + 6

Note the following combination of resistors.

The total resistance is:

Two 12 Ω in parallel = 6 Ω
Total = 6 + 12 = 18 Ω

Note the following combination of resistors.

The total resistance is:

Total of each combination of 12 and 6 = 4 Ω (calculated using the resistors in parallel formula)

Two 4 Ω in parallel gives 2 Ω

Note the following combination of resistors.

The total resistance is:

1/R = 1/12 + 1/12 + 1/6 = (1 + 1 + 2)/12 = 4/12
R = 12/4

Note the following combination of resistors.

The total resistance is:

1/R = 1/R1 + 1/R2 = 1/6 + 1/12 = (2+1)/12 = 3/12
R = 12/3

Total Score:

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