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The directed rate of flow of electric charge through any cross-section of a conductor is known as electric current.
If ∆Q charge flows in time ∆t, then current at any time t is
[q = ne]
If V is in volt, I in ampere and R is in ohm, R is the electrical resistance of the conductor.
V ∝ I
ρ of a conductor is given by, R = ρL/A, where A is the area of cross section and L, the length of the conductor. If R is in ohm, A in m2 and L in m, ρ is in ohm-metre,
Temperature and resistance: α is the temperature coefficient of resistance.
(b) Resistances in parallel
Heat produced in a conductor of resistance R, when a current I flows for t seconds = I2 Rt joules
P = ΔW/Δt
P = IV
By Ohm's Law, V = IR,
P = I2R = V2/R
(a) The sum of the currents that flow into a junction is equal to the sum of the currents that flow out of the junction.
(b) The sum of the emf’s around a loop is equal to the sum of the potential drops around the loops.
In writing V = IR = 0, the current into a node (or junction) is taken to be positive.
In applying Kirchhoff’s voltage law, if there are more than one source when the directions do not agree, the voltage of source is taken as positive, if it is in the direction of assumed current.
For null deflection in