# RRB ALP Physics Trade Notes on Current Electricity

By Neha Uppal|Updated : November 30th, 2018

### Electric Current (I) #### Electric Current Density (J) • For irregular shapes of cross-section I, J and A are all scalar quantities.

#### Electromotive Force #### Drift Velocity of Free Electrons in a Metallic Conductor • E is the applies field, e is the charge of an electron, m is the mass of an electron and t is the time interval between successive collisions (relaxation time) Mobility

• The mobility μ of a charge carrier is defined as the drift velocity per unit electric field. #### Ohm’s Law • R = Resistance of conductor
• Unit of Resistance; Volt/ampere, (Ω ohm)

#### Resistance and Resistivity

• The inverse of resistance is called conductance G. • S.I. unit Ω-1 is called Siemens (S)
• The resistance of a conductor is directly proportional to its length l and inversely proportional to the area of cross-section A. • The inverse of resistivity is called conductivity σ. • S.I. unit is Ω-1n-1 or Sm-1

#### Temperature Coefficient of Resistance • RT = Resistance at temperature T
• R0 = Resistance at temperature T0
• α = Temperature coefficient of resistance.

#### Temperature Coefficient of Resistivity (ρ)

• For conductors • For insulators • K = Boltzman constant
• T = Absolute temperature

#### Combination of Resistances

• Resistance In Series  • Resistance in Parallel  #### Internal Resistance of a Cell and Terminal Voltage #### Kirchhoff's Rule

• First Rule (Junction Rule)  • Second Rule (Loop Rule)(Based on law of conservation of energy)
• The algebraic sum of changes in potential around any closed loop must be zero.  • The metre bridge #### Shunt Resistance Required to Convert a Galvanometer into an Ammeter of Desired range   • Resistance of ammeter so obtained #### Series Resistance Required to Convert a Galvanometer into a Voltmeter of Desired Range.   is desired range and R is additional series resistance.

#### Cell in Series and Parallel #### Heating Effect of Current

• When a charge dq passes across a potential difference V, the work done dW is given by

dW = V dq

• The flow of charge dq in time dt is equivalent to current I. • According to Ohm’s Law V = Ri #### Power • Resistance of a bulb or other electrical appliances: • And maximum current that can be passed without the appliance getting fused. • Ratio of powers consumed in two resistors in series: • Ratio of powers consumed in two resistors in parallel. #### Potentiometer  • First Law
• The mass of a substance deposited or liberated at an electrode is proportional to the quantity of charge that passes through the electrolyte. • Second Law
• If the same quantity of charge is passed through several electrolytes, then the masses of various substances deposited at the respective electrodes are proportional to their chemical equivalents. • The constant F is called Faraday.

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