Say what resistors, capacitors and inductors do, read switch types like SPDT, and know which batteries recharge.
Syllabus: Fixed and variable resistors; Capacitors; Inductors; Fuses; Switches; Batteries
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
A resistor opposes the flow of current. A potentiometer is a resistor with a moving wiper: turn the knob and the resistance changes. That makes it the usual volume control.
RememberPotentiometer = adjustable resistor. What it controls is resistance.
Both store energy, in different fields. Their build tells you which is which.
| Part | Built from | Stores energy in |
|---|---|---|
| Capacitor | conductive plates with an insulator between | an electric field |
| Inductor | a coil of wire | a magnetic field |
Memory hookCapacitor = plates = electric field. Inductor = coil = magnetic field.
Pole = how many separate circuits the switch controls. Throw = how many positions each circuit can be switched to.
Exam figure T-2 shows a switch with one blade and a single gap: SPST, a plain on/off switch.
RememberSPDT: one circuit switched between one of two others.
| Rechargeable | Not rechargeable |
|---|---|
| Nickel-cadmium (NiCd) | Carbon-zinc |
| Nickel-metal hydride (NiMH) | |
| Lithium-ion | |
| Lead-acid |
Memory hookIf it is a "dry cell" carbon-zinc, use it once. Anything with nickel, lithium-ion or lead can be recharged.