What is component 2 in figure T-1?

Explication
Component 2 is the NPN transistor in Figure T-1, the device that controls current in this circuit. Component 1 is the resistor and component 3 is the lamp, while a connector is not the numbered symbol.

Component 2 is the NPN transistor in Figure T-1, the device that controls current in this circuit. Component 1 is the resistor and component 3 is the lamp, while a connector is not the numbered symbol.