Identify the non-source: Which of the following devices is not an energy source in an electrical system?

Introduction / Context:
Distinguishing between sources and passive components is a foundational skill in circuit design and troubleshooting. Energy sources provide electrical energy, while control components distribute or limit that energy. This question asks you to identify which listed device is not an energy source.

Given Data / Assumptions:

• Options include common components found in basic circuits.
• Energy sources convert some form of energy into electrical energy or store and deliver it.
• Passive control components do not create energy; they dissipate or regulate it.

Concept / Approach:

Generators, batteries, solar cells, and fuel cells either generate or store and then supply electrical energy. A rheostat is a variable resistor used to control current or adjust voltage division; it does not generate energy and instead dissipates power as heat.

Step-by-Step Solution:

Verification / Alternative check:

Power balance: sources supply net power to the circuit, while a rheostat consumes power P = I^2 * R. It cannot provide net energy to loads.

Why Other Options Are Wrong:

Generator converts mechanical to electrical energy. Battery provides stored chemical energy as electrical. Solar cell converts light to electrical energy. Fuel cell generates electricity from continuous chemical reactions.

Common Pitfalls:

Confusing control components (rheostat, potentiometer) with sources due to their effect on current; assuming any component with two terminals can be a source, which is not the case without an energy conversion/storage process.

Final Answer:

rheostat