Current Electricity Flashcards

Flashcards for Current Electricity

Current Electricity

Electricity produced by the movement of charges.

Electric Current

The rate of flow of electrical charge.

SI Unit of Electric Current

Ampere (A)

Average Current Formula

Aq/At

Instantaneous Current Formula

lim (At->0) Aq/At = dq/dt

Conventional Current Direction

Direction of positive charge flow; opposite to electron flow.

Current

Scalar quantity

Ohm's Law

Voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperature remain constant.

Resistance

Property that resists the flow of charge/current.

Resistance Formula

R = p(L/A)

Resistivity

Property of a material that resists current flow.

Conductivity

Measure of how well a material conducts electricity; inverse of resistivity.

Drift Velocity

Flow of electrons in a conductor due to an electric field.

Drift Velocity Formula

Vd = (eE/m) * T

Relaxation Time (T)

Average time elapsed between collisions of electrons.

Relationship between Current and Drift Velocity

I = n * e * A * Vd

Current Density (J)

Current flowing per unit area.

Current Density Formula

J = I/A

Mobility of Electrons (µ)

Magnitude of drift velocity per unit electric field.

Mobility Formula

µ = |Vd| / E = eT/m

Specific Resistance

Resistance of a unit length and unit area of a conductor.

Resistivity variation with Temperature

Temperature increases, resistivity also increases

Resistivity Temperature Dependence Formula

P = Po [1 + alpha(T - To)]

Limitations of Ohm's Law

The relation between V and I is not unique

Electrical Power

Electrical work / time

Electrical Power Formula

P = VI = I^2R = V^2 / R

Electrical Energy Formula

P*t = VIt

Internal Resistance (r)

Resistance offered by the electrolyte within a cell.

EMF of a Cell (E)

Potential difference between electrodes when there is no current in the cell (open circuit).

Terminal Voltage Formula (Discharging)

V = E - Ir

Charging cell

Cell's terminal P.D. is greater than its EMF

Current Drawn from a Cell (with Internal Resistance)

I = E / (R + r)

Equivalent EMF in Series Combination of Cells

Eeq = E1 + E2 + …

Equivalent Internal Resistance in Series Combination of Cells

1/Req = 1/r1 + 1/r2 + …

Equivalent EMF in Parallel Combination of Cells

Eeq = E

Equivalent Internal Resistance in Parallel Combination of Cells

1/Req = 1/r + 1/r + … (n times)

Series cells arrangement

Cells are arranged in series to increase the voltage.

Parallel cell arrangement

Cells are arranged in parallel to increase the current.

Kirchhoff's Junction Law

At a junction, the sum of currents entering the junction is equal to the sum of currents leaving the junction.

Kirchhoff's Loop Law

In a closed loop, the algebraic sum of EMFs is equal to the algebraic sum of the product of current and respective resistance flowing through them.