🔍 Key Concepts
• Use Ohm’s Law to relate voltage, current, and total resistance: V = I × R.
• Recognize from the illustration that R1 and R2 are in parallel, and that the source "sees" a single total resistance for the whole circuit with the switch closed.
• For a parallel branch, the total resistance must be less than the smallest individual resistor in that branch.
💭 Think About
• First, use the given source voltage and total current to calculate the overall circuit resistance seen by the source. What formula connects these three quantities?
• Once you know the total circuit resistance, compare it to the known value of R2 (40 ohms). For a parallel combination of R1 and R2, should the total be greater than, equal to, or less than 40 ohms?
• Looking at the answer choices, which ones could be immediately ruled out because they do not make sense for a parallel combination that includes a 40‑ohm resistor?
✅ Before You Answer
• Double-check your Ohm’s Law calculation: R_total = V / I, making sure to keep track of units (volts, amps, ohms).
• Confirm from the diagram that R1 and R2 are connected in parallel, not in series, so the total resistance must be less than 40 ohms.
• Verify that your final choice for total resistance is consistent with both the given current (0.75 A) and the source voltage (10 V).