Relay An electrically operated switch, for example a 9V battery circuit connected to the coil can switch an AC mains circuit. The rectangle represents the coil. NO = Normally Open, COM = Common, NC = Normally Closed.
Electricity is the flow of charge around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors.
LDR A transducer which converts brightness (light) to resistance (an electrical property). LDR = Light Dependent Resistor
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.