The devices which deliver electricity are called the 'sources'. Lamps, electric engines, etc. which consume electricity are called ‘loads’. Switches are used to switch the loads on and off whenever necessary. Hence, the source, the loads, and the switches are connected to form electrical circuits.
The circuit is called 'closed' when the current flows in the circuit, and when the current does not flow at all, it is called an 'open circuit'. The switch or key helps to make or break the circuit.
If the components of a circuit are connected in a single loop, so that the same current flows through all the loads then the connection is called 'series' circuit.
Series Circuit (Bulbs are in series)
Where as, if each of the components has a separate connection with a battery, then the circuit is said to be in parallel. The potential difference across the elements remain same.
Parallel Circuit (Bulbs are in parallel)
A voltmeter is a device used to measure 'potential difference' and an ammeter is a device used to measure 'current'. Ammeters are connected 'in series' to the components through which the current to be measured flows. Voltmeters are connected in parallel to the components across which the potential difference is to be measured.
To measure current through R. To measure potential difference across AB
