Revision: 11th Std >> Magnetic Effect of Electric Current MAH-MHT CET (PCM/PCB) Magnetic Effect of Electric Current

An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire.

A device that does not obey Ohm's law and shows a non-linear or direction-dependent V-I relation.

A device that obeys Ohm's law and gives a straight-line V-I graph through the origin.

The electrical energy consumed in a circuit is defined as the total work done in maintaining the current in the electric circuit for a given time.

Electrical Energy = \[VIt=I^2Rt=\frac{V^2t}{R}\]

S.I. unit of electric energy is joule (1 kWh = \[3.6\times10^6\mathrm{~J}\])

Power is defined as the rate of doing work or work done per second.

i.e., Power = `("Work done in joule")/("Times in second")`

or,  p = `("W (in joule)")/("t (in second)")`

The rate of doing work is called power.

Electrical Resistivity (ρ) is defined as the resistance offered by a conductor of unit length and unit cross-sectional area at a given temperature. It is a characteristic property of the material, independent of its dimensions.

Electromotive Force (emf) is the work done by a cell (or any energy source) in driving a unit positive charge around the complete circuit, including through the cell itself.

Power P = \[\frac{\text{Work done }W}{\text{Time taken }t}\]

or

P = \[\frac {W}{t}\]

ε = \[\frac {dW}{dq}\]

SI Unit: volt (V), where 1 V = 1 J C⁻¹
Dimensional Formula: [ML²T⁻³A⁻¹]

• S.I. unit: If 1 joule of work is done in 1 second, the power spent is said to be 1 watt.
• C.G.S. unit: The C.G.S. unit of power is erg per second (erg s^-1).
• Relationship between S.I. and C.G.S. units:
   1 W = 1 J s^-1 = 10⁷ erg s^-1
• 1 horse power (H.P.) = 746 W = 0.746 kW

• Cells are connected from the positive terminal to the negative terminal.
• Total emf is the sum of individual emfs:
  E_net = E₁ + E₂ + E₃ + ...
• Total internal resistance:
  rnet = r₁ + r₂ + r₃ + ...
• For n identical cells:
  E_net = nE
  r_net = nr
• Current in the circuit:
  \[I=\frac{E_{\mathrm{net}}}{r_{\mathrm{net}}+R}\]
• For identical cells:
  \[I=\frac{nE}{nr+R}\]