Current Calculation 42743E
1. **Problem Statement:**
Determine the current $I$ in the given circuit using Kirchhoff's Current Law (KCL).
2. **Understanding the Circuit:**
- A 12V source is connected to a 3\Omega resistor.
- After the 3\Omega resistor, the current $I$ flows upward to a node.
- From this node, the circuit splits into three parallel branches:
1) 2\Omega resistor then 11V source,
2) 1\Omega resistor to ground,
3) 2\Omega resistor then 9V source.
3. **Apply KCL at the node after the 3\Omega resistor:**
The current $I$ entering the node equals the sum of currents leaving through the three branches:
$$I = I_1 + I_2 + I_3$$
4. **Find voltages at the node:**
Let the node voltage be $V$ (with respect to ground).
5. **Express each branch current in terms of $V$:**
- Branch 1 (2\Omega and 11V source): Voltage at the far end is 11V, so current flows from node to 11V source through 2\Omega resistor:
$$I_1 = \frac{V - 11}{2}$$
- Branch 2 (1\Omega resistor to ground):
$$I_2 = \frac{V - 0}{1} = V$$
- Branch 3 (2\Omega and 9V source): Voltage at far end is 9V, current:
$$I_3 = \frac{V - 9}{2}$$
6. **Express $I$ in terms of $V$:**
$$I = \frac{V - 11}{2} + V + \frac{V - 9}{2} = \frac{V - 11 + 2V + V - 9}{2} = \frac{4V - 20}{2} = 2V - 10$$
7. **Find $I$ using the 3\Omega resistor and 12V source:**
The current $I$ flows through the 3\Omega resistor from 12V source to node at voltage $V$:
$$I = \frac{12 - V}{3}$$
8. **Set the two expressions for $I$ equal:**
$$2V - 10 = \frac{12 - V}{3}$$
9. **Solve for $V$:**
Multiply both sides by 3:
$$3(2V - 10) = 12 - V$$
$$6V - 30 = 12 - V$$
Add $V$ to both sides:
$$6V + V - 30 = 12$$
$$7V - 30 = 12$$
Add 30 to both sides:
$$7V = 42$$
Divide both sides by 7:
$$V = 6$$
10. **Find $I$ using $V=6$:**
$$I = 2V - 10 = 2*6 - 10 = 12 - 10 = 2$$
**Final answer:**
$$\boxed{I = 2\text{ A}}$$