What is component 9 in figure T2?

The correct answer is variable resistor. In circuit diagrams, variable resistors are often represented as components that allow for adjustment of resistance, influencing current flow and voltage in a circuit. These components are integral in applications where tuning or modulation of the electrical signal is required, as they can change the circuit's characteristics depending on their settings.

Variable resistors typically have two terminals, one connected to a fixed resistor and another linked to a movable contact that adjusts the resistance value. This adjustment is crucial in various applications, such as volume controls in audio equipment or in settings where precise control over electrical parameters is needed.

In the context of the question referring to component 9 in figure T2, identifying it as a variable resistor implies that it plays a role in the circuit's functionality allowing for dynamic adjustment, which is important in ham radio setups for tuning frequencies and optimizing signal quality. Understanding this component's function enhances the technician's ability to manage radio operations effectively.