3. Resistor An electrical component that limits or regulates the flow of electrical current in an electronic circuit.

6. LED Light Emitting Diode A light-emitting diode (LED) is a semiconductor device that emits visible light when an electric current passes through.

8. Photocell Component that varies in its resistance to the flow of current as a function of the amount of light falling on it.

9. Integrated Circuit (555 Timer) An integrated circuit (IC), sometimes called a chip or microchip. A semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. An IC can function as an amplifier, oscillator, timer, counter, computer memory, or microprocessor.

11. Battery A container consisting of one or more cells, in which chemical energy is converted into electricity and used as a source of power.

13. Speaker A transducer which converts electrical energy to sound.

16. Potentiometer A variable resistor with a third adjustable terminal.

17. Diode A semiconductor device with two terminals, typically allowing the flow of current in one direction only.

19. SCR Gate SCRs are unidirectional devices (i.e. can conduct current only in one direction) SCRs can be triggered normally only by currents going into the gate.

21. NPN Transistor Transistors can be regarded as a type of switch. They are central to electronics and there are two main types; NPN and PNP. Most circuits tend to use NPN. Parts The BASE - which is the lead responsible for activating the transistor. The COLLECTOR - which is the positive lead. The EMITTER - which is the negative lead.

23. PNP Transistor Positive Negative Positive

25. Ceramic Capacitor A fixed value capacitor in which ceramic material acts as the dielectric.

27. Electrolytic Capacitor A type of capacitor that uses an electrolyte to achieve a larger capacitance than other capacitor types.

29. Push Button Causes a temporary change in the state of an electrical circuit only while the switch is physically actuated. An automatic mechanism (i.e. a spring) returns the switch to its default position immediately afterwards, restoring the initial circuit condition.