A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element.
Resistors reduce the current flow and lower voltage levels within circuits.
A circuit is said to be connected in series when the same amount of current flows through the resistors. In such circuits, the voltage across each resistor is different.
In a series connection, if any resistor is broken or a fault occurs, then the entire circuit is turned off. The construction of a series circuit is simpler compared to a parallel circuit.
For the above circuit(attached image-1), the total resistance is given as:
The total resistance of the system is just the total of individual resistances.
A circuit is said to be connected in parallel when the voltage is the same across the resistors. In such circuits, the current is branched out and recombines when branches meet at a common point.
A resistor or any other component can be connected or disconnected easily without affecting other elements in a parallel circuit.
The figure(attached image -2) above shows ‘n’ number of resistors connected in parallel. The following relation gives the total resistance here
The sum of reciprocals of resistance of an individual resistor is the total reciprocal resistance of the system.
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Hope it helps you:)