CURRENT ELECTRICITY

                                  CURRENT ELECTRICITY                        

1. I = Q / t

Here I = Electric current

          Q = Electric charge

           t = time

2. S.I. unit of electric current is ampere.

3. 1 ampere = 1 coulomb / 1 second

4. 1 ampere = 3 x 10⁹ stat ampere

5. 1 ampere = 1 / 10 ab ampere

6. EMF = Work done / charge

7. Differences between EMF and POTENTIAL DIFFERENCE:

 EMF –

§  It is the work done by a source in taking a unit positive charge once round the complete circuit.

§  It is equal to maximum potential difference between the two terminals of a source when it is in an open circuit.

§  It has non – electrostatic origin.

§  It is a cause.

§  It is larger than potential differences across any circuit element.

§  It is independent of external resistance of the circuit.

POTENTIAL DIFFERENCE –

§  It is the work done by a source in taking a unit positive charge from one point to a circuit.

§  Potential difference may exist between any two points of a closed circuit.

§  It exists only when the circuit is closed.

§  It is an effect.

§  It is always less than EMF.

8. Ohm’s Law –

It states that at constant temperature, the current flowing through a conductor is directly proportional to the potential difference applied across its ends.

                                                            V = R I

Here V = Potential difference

         R = Resistance

      I = Electric current                                                            

9.        

           I

                             V

10. Limitations of Ohm’s law –

·         Ohm’s law is applicable only when the conductor is at constant temperature.

·         It is applicable only for ohmic conductor.

11. The conductor which obey Ohm’s law are called Ohmic conductors.

12. The conductor which do not obey Ohm’s law are called non-ohmic conductor.

13. R = V / I

Here R = Resistance of conductor

         V = Potential difference

         I = Electric current

14. 1 ohm = 1 volt / 1 ampere

15. R α L

Here R = Resistance

          L = Length of the conductor

16. R α 1 / A

Here A = area of cross section

17. The resistance of a conductor also depends on the nature of material.

18. S.I. unit of resistivity is Ohm metre.

19. ρ = RA / L

Here ρ = Resistivity

20. J = I / A

Here J =Current density

         I = Electric current

         A = area

21. I = ʃ J. dS

22. G = 1 / R

Here G = Conductance

          R = Resistance

23. S.I. unit of conductance is Ohm^-1 or mho or siemens (s).

24. σ = 1 / ρ

Here σ = conductivity

          ρ = Resistivity

25. S.I. unit of conductivity is Ohm^-1 metre^-1 .

26. J = E / ρ = σ E

27. V_d = a τ = -e E τ / m

Here V_d = drift velocity

          τ  = Relaxation time

28. I = e n A V_d

Here I = electric current

N = No. of electrons

A = area of cross section of the conductor

V_d = Drift velocity

29. J = e n V_d

30. R = m L / n e² τ A

31. R = ρ L / A

32. ρ = m / n e² τ

33. The resistivity of a metal increases and conductivity decreases with increase in temperature.

34. The unit of temperature coefficient of resistivity is ⁰celcius^-1.

35. For metals, temperature coefficient of resistivity is positive.

36. Resistances in Series:

If a number of resistors are connected end to end so that the same current flows through each one of them in succession, then they are said to be connected in series.

                                R s = R ₁ + R ₂ + R ₃ +………..+ R _n

ü  Current through each resistance is same.

ü  Equivalent resistance is larger than the largest equivalent resistance.

37. Resistances in Parallel:

If a number of resistances are connected in between two common points so that each of them provides a separate path for current, then they are said to be connected in parallel.

                              1 / R _p = 1 / R ₁ + 1 / R ₂ + ………. + 1 / R _n

ü  Potential drop across each resistance is same.

38. r = R ( E – V / V )

Here r = internal resistance

         R = Resistance

         E = EMF

         V = Potential difference

39. Kirchhoff’s laws –

ü  First law / Junction Rule / Current law –

              In an electric circuit, the algebraic sum of currents at any junction is zero.

            

                            ∑ I = 0

ü  Second law / Loop rule / Voltage law –

              It states that the algebraic sum of EMFs in any loop of a circuit is equal to the sum of products of currents and resistances in it.

               

                     ∑ E = ∑ I R

Here E = EMF

         R = Resistance

         I = Current

ü  The wheatstone bridge is said to be balanced when the potential difference across the galvanometer is zero so that there is no current through the galvanometer.

40. Joule’s law of electrical heating –

ü  Heat produced is directly proportional to the square of the current flowing through the conductor.

                               H α I²

ü  Heat produced is directly proportional to resistance of conductor.

                               H α R

ü  Heat produced is directly proportional to the time of flow of current.

                                H α t

41. W = V I t

Here W = Electric energy

          V = Potential Difference

          t = Time

42. P = W / t = V I = I² R = V² / R

Here V = Potential Difference

          I = Electric current

         R = Resistance

43. S.I. unit of electric power is watt.

44. 1 KW = 1000 WATT

45. 1 MW = 10⁶ WATT

46. The commercial unit of power is horse power (h p).

47. 1 h p = 746 watt

48. W = P t = I² R t

49. The commercial unit of electric energy is kilowatt hour or Board of trade (B.O.T) unit.

50. 1 K W h = 3.6 x 10⁶ joule

51. 1 W h = 3.6 x 10³ joule

https://jayphy.blogspot.com/2020/06/electric-potential-and-capacitance.html

https://jayphy.blogspot.com/2020/06/memorycapsule.html