What is component 4 in figure T-1?

The correct answer identifies Component 4 in Figure T-1 as a battery. A battery is a common electrical component that provides power to a circuit by converting chemical energy into electrical energy. It consists of one or more electrochemical cells and is essential in many electronic projects and devices, serving as the primary source of energy.

In the context of a schematic diagram, a battery is typically represented by a specific symbol that indicates its positive and negative terminals. Understanding how to recognize this symbol and its function in a circuit is crucial for interpreting diagrams accurately. In many electronic setups, a battery plays a fundamental role in supplying the necessary voltage to power various components, such as resistors, transistors, and circuits at large.

The other components listed have distinct roles within electronic circuits, with their symbols differing from that of a battery. This distinction highlights the importance of recognizing the unique functions of each component within a schematic.