Physics : Current Electricity: Summary

**SUMMARY**

·
The current, I flowing in a conductor I = dQ/dt ,where dQ is the
charge that flows through a cross-section in a time interval dt. SI unit of
current is ampere (A). 1A = 1 C s^{-1}.

·
The current density J in a conductor is the current flowing per
unit area. J = /AI

· Current is a scalar but current density is a vector.

· The general form of Ohm’s law

·
Practical form of Ohm’s law states that V ∝
I, or V = IR where I is the current.

·
The resistance R of a conductor is R = V/*I* . SI unit of resistance is ohm (Ω) and 1 Ω = 1V/1A

·
The resistance of a material R = ρ *l*/A where *l* is length of
the material and A is the area of cross section.The resistivity of a material
determines how much resistance it offers to the flow of current.

·
The equivalent resistance (R_{S}) of several resistances
(R_{1}, R_{2}, R_{3}……..) connected in series
combination is R_{S} = (R_{1}+R_{2} +R_{3}……..)

·
The equivalent resistance (RP) of several resistances (R_{1},
R_{2}, R_{3}……..) connected in parallel combination is 1/R_{P}
= 1/R_{1} + 1/R_{2} + 1/R_{3} ………………,

·
Kirchoff’s first rule (Current rule or junction rule): The
algebraic sum of the currents at any junction is zero.

·
Kirchoff’s second rule (Voltage rule or loop rule): In a closed
circuit the algebraic sum of the products of the current and resistance of each
part of the circuit is equal to the total emf included in the circuit.

·
Electric power is the rate at which energy is transformed.

·
If a current I flows across a potential difference V, the power
delivered to the circuit is P = IV.

·
In a resistor R, the electrical power converted to heat is P = I^{2}R
=V^{2}/R

·
The energy equivalent of one kilowatt-hour (kWh) is 1kWh = 3.6 X
10^{6} J.

·
Metre bridge is one form of Wheatstone’s bridge.

·
Potentiometer is used to compare potential differences.

·
Joule’s law of heating is H = VIt (or) H = I2Rt.

·
Thermoelectric effect: Conversion of temperature differences into
electrical voltage and vice versa.

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12th Physics : Current Electricity : Current Electricity: Summary | Physics

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