Theory:

Electric circuits are of three types. They are:
  • Simple circuit
  • Series circuit
  • Parallel circuit
A simple electric circuit
An electric circuit is the continuous closed path along which the current flows from the positive terminal to the negative terminal of the battery.
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Simple circuit
 
The above circuit is a simple circuit because it has simple electrical elements like a battery, bulb and a switch.
  
Construction of a circuit
A simple electric circuit consists of:
  • cell or a battery
  • Connecting wires
  • Bulb
  • Switch
Series Circuit
A circuit in which electrical elements are arranged in a chain, so that the current flows in a singlepath called a series circuit. Current is same in all the elements in the case of a series connection. If any one of the elements is damaged or disconnected, then the entire circuit will not work.
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Series connection
 
In the above diagram, all the three LEDs are connected in the form of a chain. So, they form a series connection, and hence the current flow in all the LEDs will be the same.

It is clear from the above circuit diagram that the three bulbs are connected one after the other. The way the bulbs have been combined in this circuit is called a series connection. Adding more bulbs to the circuit makes the battery worn out soon, and the brightness of the bulb is also reduced. Similarly, if we add more batteries to the circuit, the light's brightness and duration of glow will also improve.
 
Parallel circuit:
If two or more electrical elements are connected in parallel in a circuit, then the circuit is called a parallel circuit. Thus, a parallel circuit has two or more paths for the current to flow through. If any element is damaged or disconnected, the other elements will work properly without any damages.
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Parallel connection
 
In the above diagram, all the three LEDs are connected in the form of a parallel connection. As it forms a parallel connection, the current flow in all the LEDs will not be the same.