Nellie the nine-volt robot
As the name suggests, Nellie runs from a 9v PP3 battery and is an easy-to-solder kit suitable for clubs but also GCSE and A-level classes, especially as she is available in an ultra low-cost version without a battery connector (the pads on the back can touched directly against a PP3 battery or connected to a lab power supply by crocodile clips).
Why is this kit suitable for GCSE and A-level Physics classes? Well, it’s a series circuit with two LEDs, a diode and three resistors connected to a 9v battery (or a variable power supply). Students can use a voltmeter to measure the e.m.f. of the power supply and then measure the p.d. of each series component to verify Kirchoff’s Voltage Law. By calculating the combined resistance and measuring the p.d. across them, students can then use I=V/R to calculate the current flowing through the circuit. When used with a variable power supply, the experiment can be repeated at different supply voltages.