ELECTRICITY, Class X, Part- III

ACCORDING TO THE CBSE SYLLABUS 2025-26, THIS CHAPTER HAS BEEN RENUMBERED AS CHAPTER 11.

CBSE CLASS 10 SCIENCE CHAPTER 12 ELECTRICITY NOTES -(PART III)

NOTES OF CH 12 ELECTRICITY, CLASS 10TH SCIENCE

 Study Material and Notes of Ch 12 Electricity Class 10th Science

Remaining Topics of this Chapter

7. RESISTORS IN SERIES

A. TOTAL/RESULTANT/OVERALL/EFFECTIVE RESISTANCE IN SERIES
B. VOLTAGE ACROSS EACH RESISTOR

8. RESISTORS IN PARALLEL

9. ADVANTAGE OF PARALLEL COMBINATION OVER SERIES COMBINATION

10. HEATING EFFECT OF ELECTRIC CIRCUIT
A. JOULE'S LAW HEATING EFFECT OF ELECTRIC CURRENT
B. THE FILAMENT OF AN ELECTRIC BULB IS MADE UP OF TUNGSTEN
C. ELECTRIC FUSE
D. ELECTRIC POWER

COMBINATION OF RESISTANCE (RESISTOR)

Apart from the potential difference, the current in the circuit depends on the resistance. Resistances are combining or fixed put in the circuit in series and in parallel. If we want to increase the total resistance, then resistances are connected in series. If we want to decrease the total resistance, then the individual resistances are connected in parallel.

A – Series Resistance

B- Parallel Resistance

RESISTANCES (OR RESISTORS) IN SERIES

The combined resistance of any number of resistances connected in series is equal to the sum of the individual resistance, if the number of resistances is R1, R2, R3 ----Rn are connected in series, then their combined resistance R is given by. 

                                            

R = R1 + R2 + R3 +------ Rn

When a number of resistors connected in series are joined to the terminals of a battery, then each resistance has a different potential across its ends. (which depends on the value of resistance) But the total potential difference across the ends of all the resistances in series is equal to the voltage of the battery. When a number of resistors are connected in series, then the same current flows through each resistance (which is equal to the current flowing in the whole circuit.

Resultant resistance of two resistances connected on series

  

Let two resistances R1 and R2 be connected in series. A battery of V volts has been applied to the ends of this series combination. Suppose the potential difference across the resistance R1 is V1 and the potential difference across the resistance R2 is V2. The potential difference applied in the battery is V volts. So the total potential difference across the two resistances should be equal to the voltage of the battery.

 

That is,                                  V = V1 + V2  …………………………..  1

In the above circuit, the total potential difference due to the battery is V. The total resistance of the combination is R. The current flowing through the whole circuit is I, by applying Ohm’s law.

                                                V = I × R ………………………………..  2
Since the same current I flows through both the resistance R1 and R2 connected in series, we can apply Ohm’s law to both resistances separately.

                                                V1 = I × R1 ………………………………  3

                                                V2 = I × R2 ……………………………...  4

Now, putting the values of potential V, V1, and V2 from equations (2),  (3), and (4)in equation (1), we get.

                                                IR = (I × R1) + (I × R2)

                                                IR = I (R1 + R2)   

R = R1 + R2 ………………….. (Resultant Resistance in series combination)

Current through each resistor is the same.

Equivalent resistance is larger than the largest individual resistance.

Total voltage = Sum of voltage drops

 

V = V1 + V2 + V3

 

VOLTAGE ACROSS EACH RESISTOR

 

• V1 = IR1

• V2 = IR2 [V1 + V2 + V3 = V]

• V3 = IR3V = IR

⇒ V = IR1 + IR2 + IR3

∝ IR = I(R1 + R2 + R3)

∝ R = R1 + R2 + R3

 

RESULTANT RESISTANCE OF TWO RESISTORS CONNECTED IN PARALLEL

                      

Let two resistances R1 and R2 be connected in parallel to one another between the same two points A and B. A battery of V Volts has been applied across the ends.

In this type of combination. The potential difference across the ends of both resistances will be the same. The voltage in this combination is equal to the voltage in the battery.

Let the total current flowing in the circuit be I, then the current passing through the resistance R1 will be I1, and the current passing through the resistance R2 will be I2.

Therefore, the total current.

 

I = I1 + I2 ……………………..  (1)

 Suppose the resultant resistance of this parallel combination is R, then by applying Ohm’s law to the whole circuit.

V = IR

I = V/ R ------------------------(2)

Since the potential difference ‘V’ across both the resistance R1 and R2 in parallel is the same.

So by applying Ohm’s law to each resistance separately, we get.

 I1  = V/ R1  ------------------------------ (3)

I2  = V/ R2 ------------------------------- (4)

Now putting the values of I, I1 and I2 from equation (2), (3) and (4) in equation (I) we get.

 V/R = V/R1 + V/R2

V (1/R) = V(1/R1 + 1/R2)

1/R = 1/R1 + 1/R2 ---------------------(Resultant Resistance in parallel combination)

Equivalent resistance is less than the value of the smallest individual resistance in the combination.

DOMESTIC ELECTIC CIRCITS: SERIES OR PARALLEL COMBINATION

In the electric circuit, when we use it in our home, it should be in series or parallel.

SERIES COMBINATION

If we want to connect (or join) a large number of electric bulbs ( it may be hundreds or thousands) for decorating a building, trees, etc., during festivals, then the series circuit is better because all the bulbs connected in series can be controlled with just one switch. A series circuit is also safer because the current in it is smaller.

 DISADVANTAGES OF SERIES COMBINATION

If one bulb gets fused or blows off, then the circuit breaks and the entire circuit is turned off. An electrician has to spend a lot of time locating the used bulb from among hundreds of bulbs, so as to replace it and restore the lighting.

 PARALLEL CONNECTION

 The parallel connection is better for connecting bulbs (and other electrical applications) in a house because we can have separate switches for each bulb or electrical application and hence operate it separately.

 

DISADVANTAGES OF SERIES CIRCUIT FOR DOMESTIC WIRING

1.     In a series circuit, if one electrical appliance stops working due to a defect, then all other appliances also stop working.

2.     In a series circuit, all the electrical appliances have only one switch, due to which they cannot be turned on or off separately.

3.     In a series circuit, the appliances don’t get the same voltage (220 V) as that of the power supply line; the voltage is shared by all appliances, and the appliances get less voltage and hence don’t work properly.

4.     In the series connection of electric appliances, the overall resistance of the circuit increases too much, due to which the current from the power supply is low.  

ADVANTAGES OF PARALLEL COMBINATION OVER SERIES COMBINATION

 (i) In a series circuit, when one component fails, the circuit is broken and none of the component works.

(ii) Different appliances have different requirements for current. This cannot be satisfied in series as the current remains the same.

(iii) The total resistance in a parallel circuit is decreased.

EMF AND TERMINAL VOLTAGE

a. EMF: The potential difference between the two terminals of a cell when there is no current flowing through the circuit.

b. Terminal voltage: The potential difference between the two terminals of a cell when current is flowing through the circuit. ​​

 





 



 



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