Physics Current Electricity

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Current Electricity

Electrice cell or Battery

Cell is a device which converts chemical energy into electrical energy and also electrical energy into chemical .Cell is a
source of constant emf but not constant current.

`text( Emf of cell)` (E): The potential difference across the tenninals of a cell when it is not supplying any
current (open circuit ) is called it's emf.

`text( Potential difference)` (V) : The voltage across the terminals of a cell when it is supplying current to
external resistance is called potential difference or terminal voltage.
When cell discharges, its terminal potential is less than its Emf and in this chemical energy is converted into electrical energy.
When cell is being charge its terminal potential is more than its Emf and in this electrical energy is converted into chemical energy.

`text( Internal resistance )`(r) : In case of a cell the opposition of electrolyte to the flow of current through it
is called internal resistance of the cell. The internal resistance of a cell depends on the distance between
electrodes `(r prop d)`. area of electrodes `[r prop 1/A]` and nature, concentration `(r prop C)` and temperature of
electrolyte `[r prop( 1/text(temp)))`

`text(A cell is said to be ideal, if it has zero internal resistance.)`

Cell is a device which converts chemical energy into electrical energy and also electrical energy into chemical .Cell is a
source of constant emf but not constant current.

`text( Emf of cell)` (E): The potential difference across the tenninals of a cell when it is not supplying any
current (open circuit ) is called it's emf.

`text( Potential difference)` (V) : The voltage across the terminals of a cell when it is supplying current to
external resistance is called potential difference or terminal voltage.
When cell discharges, its terminal potential is less than its Emf and in this chemical energy is converted into electrical energy.
When cell is being charge its terminal potential is more than its Emf and in this electrical energy is converted into chemical energy.

`text( Internal resistance )`(r) : In case of a cell the opposition of electrolyte to the flow of current through it
is called internal resistance of the cell. The internal resistance of a cell depends on the distance between
electrodes `(r prop d)`. area of electrodes `[r prop 1/A]` and nature, concentration `(r prop C)` and temperature of
electrolyte `[r prop( 1/text(temp)))`

`text(A cell is said to be ideal, if it has zero internal resistance.)`

Cell in various Positions

`text(Closed circuit:)` Cell supplies a constant current in the circuit.

(i) Current given by the cell `i =E/ (R + r)`
(ii) Potential difference across the resistance` V = iR`
(iii) Potential drop inside the cell `= ir`
(iv) Equation of cell `E =V + ir (E> V)`
(v) Internal resistance of the cell `r = (E/V -1) R`
(vi) Power dissipated in external resistance (load) `P = Vi = i^2R = V^2 /R = (E/(R+r))^2 R`

Power delivered will be maximum when R = r ie external resistance equal to internal resistance `P_(max) = E^2/4r`
Known as maximum power theorem.
`text(Open circuit:)`
When no current is taken from the cell it is said to be in open circuit.
(i) Current through the circuit `i = 0`
(ii) Potential difference between A and B, `V_(AB) = E`
(iii) Potential difference between C and D, `V_(CD)= 0`

`text(Short circuit:)`
If two terminals of cell are join together by a thick conducting wire.
(i) Maximum current (called short circuit current) flows momentarily `i_(sc) = E/r`
(ii)Potential difference V = 0

`text(Closed circuit:)` Cell supplies a constant current in the circuit.

(i) Current given by the cell `i =E/ (R + r)`
(ii) Potential difference across the resistance` V = iR`
(iii) Potential drop inside the cell `= ir`
(iv) Equation of cell `E =V + ir (E> V)`
(v) Internal resistance of the cell `r = (E/V -1) R`
(vi) Power dissipated in external resistance (load) `P = Vi = i^2R = V^2 /R = (E/(R+r))^2 R`

Power delivered will be maximum when R = r ie external resistance equal to internal resistance `P_(max) = E^2/4r`
Known as maximum power theorem.
`text(Open circuit:)`
When no current is taken from the cell it is said to be in open circuit.
(i) Current through the circuit `i = 0`
(ii) Potential difference between A and B, `V_(AB) = E`
(iii) Potential difference between C and D, `V_(CD)= 0`

`text(Short circuit:)`
If two terminals of cell are join together by a thick conducting wire.
(i) Maximum current (called short circuit current) flows momentarily `i_(sc) = E/r`
(ii)Potential difference V = 0

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