Electric Resistance and OHM's Law

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Electric current is the rate of flow of charge. Formula: I = Q/t ; instantaneous I = dQ/dt Units: I in ampere (A), Q in coulomb (C), t in second (s) Meaning: 1 A = 1 C s^-1.

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Given: Q = 12 C, t = 3 s Formula: I = Q/t Step 1: I = 12 C / 3 s Step 2: I = 4 C s^-1 Answer: I = 4 A…

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Current adds arithmetically at a junction, regardless of angle. If two currents I1 and I2 meet at angle θ, their sum is taken as I1 + I2. That is why current is a scalar quantity, while current densit…

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Formula: I = n e A vd Where n = free electron density, e = charge of electron, A = cross-sectional area, vd = drift velocity This shows current depends on the number of charge carriers, their charge, …

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Given: n = 10^29 m^-3, e = 1.6 x 10^-19 C, A = 2 x 10^-6 m^2, vd = 10^-5 m s^-1 Formula: I = n e A vd Step 1: I = (10^29)(1.6 x 10^-19)(2 x 10^-6)(10^-5) Step 2: I = 3.2 x 10^-1 A Answer: I = 0.32 A…

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Current density is the current flowing per unit cross-sectional area at a point. Formula: j = I/A Vector form: j is a vector quantity, and its direction is the direction of motion of positive charge.

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Given: I = 5 A, A = 2 x 10^-4 m^2 Formula: j = I/A Step 1: j = 5 A / (2 x 10^-4 m^2) Step 2: j = 2.5 x 10^4 A m^-2 Answer: j = 2.5 x 10^4 A/m^2…

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Drift velocity is the average velocity with which free electrons drift towards the positive end of a conductor under an applied electric field. Formula: vd = a tau = -(e tau/m) E Meaning: the directio…