The voltage drop across R_{d} is 8 V. What is the current across R_{e}?

A. 2 A

B. 8 A

C. 14 A

D. 32 A

##### Click for Explanation

This problem requires 3 electrical circuit concepts:

1) V = IR, which relates voltage, current, and resistance

2) The fact that the voltage drop across resistors in parallel is equal in each resistor

3) Kirchoff’s junction law, which states that the sum of currents entering a node equals the sum of currents leaving a node

The voltage drop is equivalent for each resistor between red nodes A and B. The voltage drop across R_{d} is given as 8 V, and therefore the voltage drop across resistors R_{b }and R_{c} is also 8 V. Using V = IR for each resistor, the current in resistor R_{b} = 4 A, R_{c} = 8 A, and R_{d} = 2A. Using Kirchoff’s current law at node B: 4 A + 8 A + 2 A = 14 A. The current leaving node B equals the current across R_{e} because there are no other nodes in between.

A. 2 A, incorrect, this implies that the current across R_{d} = R_{e}.

B. 8 A, incorrect, this implies that the current across R_{d} equals the voltage and the current across R_{e}.

**C. 14 A, correct.**

D. 32 A, incorrect, this answer incorrectly assumes a voltage of 8 V across R_{e} and then uses a false relationship VR = I.

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