Ch 3: Current Electricity

Define electric current

the flow of charges in a wire through a cross section per unit time (ampere)

electric current formula

I=q/t (Ampere A)

define ohms law

the current flowing through a conductor is directly proportional to the potential diff across its ends (volts)

ohms law formulas

V=IR, R=V/I (volts-V)

Resistance (def/formulas)

property of conductors to resist the flow of current (ohms)

r= ρ l/a (ohms-Ω)

Define thermal velocity

the velocity in which free electrons randomly move with high speeds (10^5m/s) in a metal. The avrg thermal velocity in wire is zero

Define Drift velocity

the velocity in which free electrons move with when a potential diff is applied across the conductor in the opposing direction of the electric field

Drift velocity formula

Vd=-eE/m τ

What is the relationship b/w current and drift velocity in a conductor?

i=neAVd

define relaxation time

the time interval b/w successive collisions of electrons with the positive ions in the metallic lattice

τ=λ / Vrms

Define mobility

magnitude of drift velocity per unit electric field applied

μ=Vd/E (m² s^-1 v^-1)

Define Current density

The amount of current flowing through the conductor per unit cross-sectional area

J=i/a

Conductance

measure of ease of flow of electrons in conductor Reciprocal of resistance (G)

G=1/R (Siemen-S)

temperature dependance of resistance

R(T) = R₀ [1 + α (T - T₀) ]

temperature dependance of resistivity

ρ(T) = ρ₀[1 + α (T - T₀)]

Define Cells

A device which converts chemical energy into electrical energy. Its a source of constant voltage but not current

EMF of cells

the potential difference across the cell when it’s not supplying any current (volts)

E=V+Ir

Potential Difference of a cell

The potential diff across the the cell when its supplying current to the external resistance (volts)

V=E-Ir

Internal Resistance

The obstruction/resistance in the electrolyte of the cell in the path of electric current

What does the internal resistance of a cell depend on?

The internal resistance of a cell depends on factors such as the electrolyte concentration (α C), temperature (α 1/T), and electrode area (α 1/A).

Current in the cell formula (relation b/w V, I, and R)

I=E/R+r

What is Kirchhoff's junction rule or current law?

Kirchhoff's junction rule states that the total current entering a junction in a circuit must equal the total current leaving the junction.

What is Kirchhoff's loop rule, also known as the voltage law?

Kirchhoff's loop rule states that the sum of the voltages around any closed loop in a circuit must equal zero.

Wheatstone bridge Formula

if balanced i.e galvanometer readings shows 0

p/q=r/s that is ps=rs

Electric Energy (def+formula)

The work done by any source to maintain the electric current in the circuit

E=VIT=I²RT=TV²/R (Joules-J)

Electric Power (def+formula)

Its the rate of work done by a source

P=W/t=VI=Vq/t (Watt-W)

Electrical Heating

When current I flows through conductor of resistor R in time t, heat produced is

H=i²Rt (Joule) =i²Rt/4.18 cal