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# Physics - Current Electricity Notes for JEE Main 2015

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# Physics - Current Electricity Notes for JEE Main 2015

Physics - Current Electricity Notes for JEE Main 2015 by enexa.com

Physics - Current Electricity Notes for JEE Main 2015 by enexa.com

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### Physics - Current Electricity Notes for JEE Main 2015

1. 1. 9011041155 / 9011031155 Current Electricity Ohm’s law is insufficient to calculate currents and voltages in complicated circuits. Containing more than one energy sources and current carrying branches. Thus Kirchhoff’s laws are used. 1
2. 2. 9011041155 / 9011031155 Kirchoff’s Laws 1. Kirchoff’s Current Law ( KCL ) / Junction Law Statement Algebraic sum of the currents flowing through any node is always zero. i.e. ΣI= O ∙ Node is a point, where more than 2 connections meet. It is also known as junction. 2 Convention ∙ The currents flowing towards the node are considered positive.
3. 3. 9011041155 / 9011031155 ∙ The currents leaving / moving away from the node are considered negative. i.e. I1 + I2 – I3 – I4 – I5 = 0 ∴ I1 + I2 = I3 + I4 + I5  Current is the amount of charge flowing per second.  ( I1 + I2 ) is the amount of change approaching the node in 1sec and (I3 + I4 + I5) is the amount of change leaving the junction in 1sec. 3
4. 4. 9011041155 / 9011031155  The junction is neither consuming nor adding the change. 2. Kirchoff’s Voltage Law (KVL) / Theorem of loop Statement Algebraic sum of e.m.f’s along any closed loop is equal to sum of the products of current and resistance in that part of the loop. i.e. ΣE = ΣIR ∙ Applicable to any loop individually. 4 Convention  Current flowing in the opposite direction in which the loop is traced is considered positive. The current in the same direction is considered negative.
5. 5. 9011041155 / 9011031155  The e.m.f. which tends to circulate current in the same direction in which the loop is stretched is considered positive and the e.m.f. which tends to circulate current in the opposition direction is considered negative. There are 3 loops. 1. ABCDEFA 2. ABCFA 5 3. FCDEF
6. 6. 9011041155 / 9011031155 6 For loop, ABCDEFA - E1 +I1 R1 - I2 R2 + E2 - I2 R3 + I1R4 = O ∴ E2-E1= I2 (R2 + R3) – I1 (R1 + R4). i.e. ΣE = ΣIR Justification  e.m.f. is the energy spent by the cell to circulate unit charge once through the entire loop.  Product of current and resistance is the voltage across the resistor which is the energy spent to circulate unit charge once through that resistor.  Hence L.H.S of the equation gives the total amount of energy supplied by the cells & R.H.S is the total amount energy used by the loop.
7. 7. 9011041155 / 9011031155 According to the law of conservation of energy, these energies are equal. i.e. ΣE = ΣIR • Ask Your Doubts • For inquiry and registration, call 9011041155 / 7 9011031155.