**Combination of Resistances(or Resistors)**

**Resistors in Series:-**

**Above picture shows the combination of resistors in series.**

**V = V1 + V2 + V3**

**Applying the Ohm’s law to the entire circuit, we have ** **V = I R**

**V1 = I R1 **

**V2 = I R2 **

and **V3 = I R3**

**I R = I R1 + I R2 + I R3**

**Rs = R1 +R2 + R3**

**so, when resistors are connected in series the equivalent resistance is the sum of the individual resistors**.

**Resistors in Parallel:-
**

**The above picture shows the combination of resistors in parallel.**

**Total current i.e. I = I1 + I2 + I3**

**By applying Ohm’s law to the parallel combination of resistors, we have I = V/Rp**

**On applying Ohm’s law to each resistor, we have I1 = V /R1; I2 = V /R2; and I3 = V /R3**

**we have V/Rp = V/R1 + V/R2 + V/R3**

**or**

**1/Rp = 1/R1 + 1/R2 + 1/R3**

**so, we conclude that when resistors are connected in parallel, then the effective resistance is the sum **

Problem – A 6 ohm resistance wire is doubled up by folding. Calculate the new resistance of the wire.

The new resistance of the doubled up wire is 1.5 Ohm.

**we will now study about Electric Power and how electric appliances produces heat or how electricity produces heat. **

- In the circuit diagram given alongside, find : (i) total resistance of the circuit, (ii) total current flowing in the circuit, and (iii) the potential difference across R1

2. A 5 V battery is connected to two 30 ohm resistors which are joined together in series.

(a) Draw a circuit diagram to represent this. Add an arrow to indicate the direction of conventional current flow in the circuit.

(b) What is the effective resistance of the two resistors ?

(c) Calculate the current that flows from the battery.

(d) What is the p.d. across each resistor ?