Energy, Electricity and Electronics
Energy sources and transfer
Distinguish renewable from non-renewable sources and know that energy is transferred, not used up. Understand efficiency as useful output divided by total input, expressed as a percentage, and that losses usually appear as heat or sound. Know the difference between a primary source (fuel, wind, sunlight) and a secondary form (electricity).
Electrical fundamentals
Learn Ohm's law, voltage equals current multiplied by resistance, with units of volts, amperes and ohms. Know series circuits (current the same, voltages add, total resistance adds) and parallel circuits (voltage the same, currents add). Power equals voltage multiplied by current. A common trap is adding resistances in parallel as if they were in series.
Components and systems
Recognise resistors, capacitors, diodes, LEDs, transistors, switches, batteries and sensors. An LED needs a series resistor to limit current. Understand system blocks: input, process and output, and the need for a power supply and, where relevant, a driver stage such as a transistor for a motor.
Worked example: an LED resistor
A 9 V battery supplies an LED with a forward voltage of 2 V and a desired current of 15 mA. Resistor voltage is 9 minus 2, which is 7 V. Resistance is voltage divided by current, so 7 divided by 0.015, giving about 467 ohms. Choose the next preferred value up, 470 ohms, which keeps the current at or below the target.
Rule of thumb
Convert milliamps to amps before calculating, and check the answer's magnitude seems sensible.