Question

Define law of combination of resistors in parallel and law of combination of resistors in series .

Answer 1

Resistance can be joined to each other by two ways:
1. Series combination
2. Parallel combination
SERIES COMBINATION
If different resistances are joined with each other such that there is only one path for the flow of electric current then the combination of such resistances is called Series Combination.
In series combination current through each resistor is constant.
In series combination Potential difference across each resistor is different depending upon the value of resistance.
Equivalent resistance of circuit is equal to the sum of individual resistances.

Re = R1 + R2 + R3 + R4 + …………….. Rn

Consider three resistances R1, R2, & R3 connected in series combination with a power supply of voltage.
Potential difference of each resistor is V1, V2, & V3 respectively. Let electric current I is passing through the circuit.
Now
V = V1 + V2 + V3
According to Ohm’s law V = IR
thus
IRe = IR1 + IR2 + IR3
Re = R1 + R2 + R3

PARALLEL COMBINATION
If there are more than one path for the flow of current in a circuit then the combination of resistances is called Parallel Combination.
In parallel combination current through each resistor is different.
Potential difference across each resistor is constant.

Consider three resistances R1 , R2 & R3 connected in parallel combination with a power supply of voltage V.
Now
I = I1 + I2 + I3
according to Ohm’s law
V/R = I
Therefore,
V/Re = V/R1 + V/R2 + V/R3

1/Re = 1/R1 + 1/R2 + 1/R3

Answer 2

Explanation:

1.different resistances are joined with each other such that there is only one path for the flow of electric current then the combination of such resistances is called Series Combination. 2. ... Equivalent resistance of circuit is equal to the sum of individual resistances.