## Electricity - Important Points To Remember

CBSE Class 10 - Physics

Electric current is defined as the amount of charge flowing through a particular cross section area in a unit time.

The SI unit of electric current is ampere.

A stream of electrons moving through a conductor constitutes an electric current. In a conventional current, the direction of current is taken opposite to the direction of flow of electrons i.e. flow of positive charges from +ve terminal to -ve terminal.

1 A is the flow of 6.25 × 10¹⁸ electrons per second, or 1 coulomb per second.

Electric potential difference between points in an electric circuit is the work done to move a unit positive charge from one point to another.

The difference in electric potential between two points is called potential difference. It is measured in volts (V).

To set the electrons in motion in an electric circuit, we use a cell or a battery. A cell generates a potential difference across its terminals.

A multi-meter is an electronic measuring instrument that combines several measuring functions (electric potential difference, electric current and electric resistance) in one unit.

An instrument called ammeter  measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured.

The voltmeter is always connected in parallel across the points between which the potential difference is to be measured.

An instrument used to detect presence and direction of current flowing is called a galvanometer.

The property of a material that resists electric current, is called resistance and it measured in ohms (Ω). Resistance is the opposition that a substance offers to the motion of electrons.

Ohms law: The current through a conductor element is proportional to the potential difference applied between its ends, provided the temperature remains constant. Mathematically V=IR.

Ohm’s law is valid for metal conductors at constant temperature. It is not applicable for gaseous
conductors and semiconductors.

Resistance of a wire depends on the material of the wire, its length and its area of cross section R α l/A.

A potential difference of 1 V across a resistance of 1 Ω produces a current of 1 A.

The equivalent resistance of several resistors in series is equal to the sum of their individual resistances.

A set of resistors connected in parallel has an equivalent resistance Rₚ given by
1/Rₚ = 1/R₁ + 1/R₂ + 1/R₃ + ...

The electrical energy dissipated in a resistor is given by W = V × I × t

The unit of power is watt (W). One watt of power is consumed when 1 A of current flows at a potential difference of 1 V.

21 Electrical energy is the product of power and time. Units of electrical energy W-s and KWH.

22 The commercial unit of electrical energy is kilowatt hour (kWh).
1 kW h = 3,600,000 J = 3.6 × 10 6 J.  1. 2. 