## Electricity - Important Points To Remember

*CBSE Class 10 - Physics*

①

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

② The SI unit of electric current is

**ampere**.

③ 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.

④

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

⑤

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

⑥ The difference in electric potential between two points is called potential difference. It is measured in

**volts (V)**.

⑦ 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.

⑧ A

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

⑨ 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.

⑩ The

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

⑪ An instrument used to detect presence and direction of current flowing is called a

**galvanometer**.

⑫ 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.

⑬

**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.

⑭ Ohm’s law is valid for metal conductors at constant temperature. It is not applicable for gaseous

conductors and semiconductors.

⑮ Resistance of a wire depends on the material of the wire, its length and its area of cross section

**R α l/A**.

⑯ A potential difference of

**1 V**across a resistance of 1 Ω produces a current of 1 A.

⑰ The equivalent resistance of several

**resistors in series**is equal to the sum of their individual resistances.

⑱ A set of

**resistors connected in parallel**has an equivalent resistance Rₚ given by

1/Rₚ = 1/R₁ + 1/R₂ + 1/R₃ + ...

⑲ The

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

⑳ 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

1 kW h = 3,600,000 J = 3.6 × 10 6 J.

**kilowatt hour (kWh)**.1 kW h = 3,600,000 J = 3.6 × 10 6 J.