1. If a net charge Q, flows across any crosssection of a conductor in time t, then the current I, through the crosssection is I = Q/t Q = It 2. The electric potential difference between two points in an electric circuit carrying some current is the work done to move a unit charge from one point to the other – Potential difference (V) between two points = Work done/Charge V = W/Q W = VQ 3. Q = n x Charge on 1 electron When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’. 4. If the current I, flowing in a metallic wire and the potential difference across its terminals is V . Then potential difference, V, across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same. This is called Ohm’s law. V a I Þ V = RI or, I = V/R 5. Resistance of the conductor depends (i) on its length, (ii) on its area of crosssection, (iii) on the nature of its material and (iv) temperature R a l/A R = r l/A Or, r = RA/l 6. If resistors joined in series: V = V1 + V2 + V3 but I = I1 = I 2 = I 3 Then R = R 1 + R 2 + R 3 6. If resistors joined in Parallel: V = V1 = V2 = V3 but I = I1 + I 2 + I 3 Then 1/R = 1/R 1 + 1/R 2 + 1/R 3 7. If a current I flowing through a resistor of resistance R. and the potential difference across is V for time t sec Then, the work done in moving the charge Q through a potential difference V is W= VQ. But, Q = It W = V I t (i) Now, Power = work done / Time P = W/t {or, W = Pt [The energy supplied to the circuit by the source in time t is P × t = V I t] P = V I t /t [ Using eq. (i) ] P = VI  (ii) The amount of heat produced in time t = H H = the energy supplied to the circuit by the source in time t = V I t Applying Ohm’s law, V = IR H = I2 R t Note: heat produced in a resistor is (i) Directly proportional to the square of current for a given resistance, (ii) Directly proportional to resistance for a given current, and (iii) Directly proportional to the time for which the current flows through the resistor. 8. Electric Power: The rate at which electric energy is dissipated or consumed in an electric circuit is called electric power. The power P is given by P = VI Using, V = IR Þ P = I2R = V2/R Also using, V/R = I Þ P = V2/R 9. The commercial unit of electric energy is kilowatt hour (kW h) = 1 unit. 10. 1 kW h = 1000 watt × 3600 second = 3.6 × 106 watt second = 3.6 × 106 joule (J) Now start practicing these Numerical: Click here To View
2 Comments
3/5/2013 06:39:48 am
Very useful article written, interesting and valuable .Always expecting such a informative blog from you.I found nowhere such kind of skillful writing.
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1/10/2013 06:22:28 pm
Very useful article written, interesting and valuable .Always expecting such a informative blog from you.
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