Voltage Drop
1. **State the problem:** Use the Superposition theorem to calculate the voltage drop across the 3 \(\Omega\) resistor in the given circuit.
2. **Identify sources:** The circuit has two current sources (15 A each, opposite directions) and one voltage source (20 V).
3. **Superposition theorem:** Analyze the circuit by considering one independent source at a time while replacing others with their internal resistances (current sources open-circuited, voltage sources short-circuited).
4. **Step 1: Consider only the 20 V voltage source.**
- Replace both 15 A current sources with open circuits.
- The circuit reduces to a series-parallel resistor network with the 20 V source.
- Calculate equivalent resistance and current through the 3 \(\Omega\) resistor.
5. **Calculate equivalent resistance:**
- The 1 \(\Omega\) and 2 \(\Omega\) resistors are in series: \(R_{12} = 1 + 2 = 3\ \Omega\).
- The 6 \(\Omega\) resistor is in parallel with \(R_{12}\):
$$R_{p} = \frac{6 \times 3}{6 + 3} = \frac{18}{9} = 2\ \Omega$$
- The total resistance in series with the 3 \(\Omega\) resistor is:
$$R_{total} = 2 + 3 = 5\ \Omega$$
6. **Calculate current from 20 V source:**
$$I = \frac{V}{R_{total}} = \frac{20}{5} = 4\ A$$
7. **Voltage drop across 3 \(\Omega\) resistor (due to 20 V source):**
$$V_{3,1} = I \times 3 = 4 \times 3 = 12\ V$$
8. **Step 2: Consider only the 15 A current sources.**
- Replace the 20 V voltage source with a short circuit.
- The two 15 A current sources are in opposite directions; their net effect is zero current in the middle branch.
- Therefore, no current flows through the 3 \(\Omega\) resistor from the current sources alone.
9. **Voltage drop across 3 \(\Omega\) resistor (due to current sources):**
$$V_{3,2} = 0\ V$$
10. **Step 3: Combine results using superposition:**
$$V_3 = V_{3,1} + V_{3,2} = 12 + 0 = 12\ V$$
**Final answer:** The voltage drop across the 3 \(\Omega\) resistor is \(\boxed{12\ V}\).