NCERT Class 10 The most Important Basic concepts of chapter 12 Electricity (part-2)

The most Important points of Electricity (part-2)

23. Ohm's law: This law States that the current passing through a conductor is directly proportional to the potential difference across its ends, provided the physical conditions like temperature, density etc., remain unchanged 

               V ⋉ I      or      V = RI

The proportionality constant R is called resistance of the conductor.

24. Resistance: It is the property of a conductor by virtue of which it opposes the flow of current through it. It is equal to the ratio of the potential difference applied across its ends and the current flowing through it.

   Resistance = potential difference / current

                   R = V / I

25. Ohm: It is the SI unit of resistance. A conductor has a resistance of one Ohm if a current of one ampere flows through it on applying a potential difference of 1 volt across its ends.

                 1 ohm = 1 volt / 1 ampere

                       1Ω = 1V / 1 A

26. Resistor: A conductor which has some appreciable resistance is called a Resistor.

27. Factors on which resistance of a conductor depends: The resistance R of a conductor depends on its length L, area of cross-section A and the nature of its material. It is given by 

                        R  =  ρ L/A

The proportionality constant  ρ is called resistivity of the conductor.

28. Resistivity: It is defined as the resistance offered by a cube of a material of side 1m when current flows perpendicular to its opposite faces. It's SI unit is ohm-metre(Ωm)

          Resistivity, ρ = RA / L

29. Resistance in series: When two or more resistances are joined end to end so that same current flows through each of them in turn, they are said to be connected in series. Here, the total resistance is equal to the sum of the individual resistances.

        Rs = R1 + R2 + R3 + ......

30. Resistance in parallel: When two or more resistances are connected across two points so that each of them provides a separate path for current, they are said to be connected in parallel. Here the reciprocal of their combined resistance is equal to the sum of the reciprocals of the individual resistances.

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

31. Heating effect of current: When an electric current is passed through a conductor, heat is produced in it. This is known as heating effect of Electric current. 

32. Joule's law of heating: It states that the heat produced in a conductor is directly proportional to 

(i) The square of the current I through it

(ii) Proportional to its resistance R 

(iii) The time t for which current is passed.

Mathematically it can be expressed as 

       H = I²Rt joule

       H = VIt joule

33. Electric energy: It is the total work done in maintaining an electric current in an electric circuit for a given time.

       Electric energy, W = VIt = I²Rt joule

34. Electrical power: Electrical power is the rate at which electric energy is consumed by an appliance.

       P =  W / t =  VI =  I²R =  V²/R

35. Watt: It is the SI unit of power. The power of an appliance is 1 watt if one ampere of current flows through it on applying a potential difference of 1 volt across its ends.

     1 watt = 1 joule / 1 second

         1 W = 1Js-¹  or    1J/s

      1 kilowatt = 1000W.

36. Kilowatt hour: It isbthe commercial unit of Electrical energy. One kilowatt hour is the electric energy consumed by an appliance of 1000 watts when used for one hour. 

      1 kWh = 3.6 × 10⁶ J

37. Power rating: The power rating of an appliance is the electric energy consumed per second by the appliance when connected across the marked voltage of the mains. 

38. Efficiency of an electric device: It is the ratio of the output power to the input power. 

    Efficiency,η = Output power / Input power