Question

Five current carrying conductors meet at point P. What is the magnitude and direction of the current in conductor PQ?

• A. 1 A form Q to P
• B. 1 A form P to Q
• C. 3 A form P to Q
• D. 2 A form Q to P

Hint:

Physics Tip : Kirchhoff's First Law is a statement of the conservation of charge; charge cannot accumulate at a junction point.

Answer 1

The Correct Option is B

Concept: Physics (Current Electricity) – Kirchhoff's First Law (Junction Law).

Step 1: State Kirchhoff's First Law. At any junction point P, the sum of currents entering the junction is equal to the sum of currents leaving the junction ($\sum I = 0$).

Step 2: Set up the junction equation for point P. Based on the diagram: * Entering Currents: $5\text{ A}$ and $4\text{ A}$ * Leaving Currents: $5\text{ A}$ and $3\text{ A}$ * Let $I$ be the current in conductor PQ. The equation is: $5\text{ A} + 4\text{ A} + I - 5\text{ A} - 3\text{ A} = 0$.

Step 3: Solve for $I$ and determine direction. * $9\text{ A} + I - 8\text{ A} = 0$ * $1\text{ A} + I = 0 \implies I = -1\text{ A}$ * A negative sign indicates that the assumed direction was inward; therefore, a $1\text{ A}$ current flows from P to Q. $$ \therefore \text{The current in PQ is 1 A flowing from P to Q.} $$