Electronics Engineering (ELEX) Board Practice Exam

In the given circuit, what is the value of R_L for maximum power transfer?

1. 1.4 Ω

2. 2.0 Ω

3. 2.8 Ω

4. 3.2 Ω

The correct answer is: 2.8 Ω

For maximum power transfer in a circuit, the load resistance \( R_L \) needs to be equal to the Thevenin equivalent resistance, \( R_{th} \), looking back into the circuit from the load. This principle is known as the Maximum Power Transfer Theorem. To solve for \( R_L \), one typically analyzes the circuit to find \( R_{th} \). If the circuit components and their arrangement allow for an easy identification of the equivalent resistance, matching the load resistance to this equivalent value will ensure that the load receives the maximum possible power. If \( R_{th} \) is computed and is found to be 2.8 Ω, then setting \( R_L \) to this value will maximize the power being transferred to the load. In practical scenarios, this often requires simplifying the circuit using series and parallel resistance combinations, but the underlying principle that drives this calculation is always the same: the load resistance should equal the Thevenin resistance for optimal power delivery. Thus, when the correct answer indicates that \( R_L \) is 2.8 Ω, it aligns with this theoretical foundation, confirming that for maximum efficiency in power transfer, the load should indeed match the equivalent resistance of the source