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Sunday, February 13, 2011

OHM'S LAW......

The Ohm's Law states that for a metallic conductor, at constant temperature, the ratio of the potential difference ratio V to the electrical current I is constant.This is the Ohm’s Law that can be expressed by
V/I = R or V = RI

Resistors can be combined in two kinds of arrangements: series and parallel. In the series combination the same current "I" flows along each resistor. The potential drop across each resistor, according to Ohm’s law, is V1 = R1I, V2 = R2I,….., Vn = RnI. The overall potential difference is
V = V1 + V2 + ……. + Vn = (R1 + R2 + ….. + Rn)I
The system can be replaced for a single resistor R satisfying V = IR. Therefore
R = R1 + R2 + …..+ Rn

In the parallel combination the resistors are connected in such a way that the potential difference V is the same for all of them. The current through each resistor, according to Ohm’s law, is 

I1 = V/R1, I2 = V/R2, ……, In = V/Rn.

The total current "I" supplied to the system is

I = I1 + I2 +……+ In = (1/R1 + 1/R2 + …… + 1/Rn)V

The system can be replaced for a single resistor R satisfying
I = V/R. Therefore,

1/R = (1/R1 + 1/R2 + …… + 1/Rn) 

An emf source of 6.0V is connected to a purely resistive lamp and a current of 2.0 amperes flows. All the wires are resistance-free. What is the resistance of the lamp?

The gain of potential energy occurs as a charge passes through the battery, that is, it gains a potential of V =6.0V. No energy is lost to the wires, since they are assumed to be resistance-free. By conservation of energy, the potential that was gained  must be lost in the resistor. So, by Ohm's Law:
    V = I RR=V/I R = 3.0 


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