Oscilloscope An oscilloscope is used to display the shape of electrical signals - showing how they vary with time. It can be used to measure voltage and time periods.
Resistor A resistor restricts the flow of charge. Uses include limiting the current passing through an LED, and slowly charging a capacitor in a timing circuit. Some publications use the old resistor symbol
Phototransistor A light-sensitive transistor.
The diagram shows a simple circuit of a battery, wires, a switch and a lamp. The switch works by breaking the circuit.