ELECTRICITY

ELECTRICITY

1. Atomic Structure

   • An atom has positively charged nucleus, and negatively charged electrons moving around it. Valence electrons constitute an electric current.

2. Charge

   • The charge is an intrinsic property of matter by virtue of which it can exert electromagnetic force.

3. Conductors and Insulators

   • A substance which offers comparatively less opposition to the flow of current is known as conductors and substances which offer larger opposition are insulators.

4. Electric Potential and Potential Difference

   • The electric potential at a point is defined as work done in bringing a unit positive charge from infinity to that point. The potential difference between two points is defined as the difference in electric potentials at the two given points.

5. Electric Current

   • Flow of electric charges is called electric current, i.e, I = Q/t .

6. Electric Circuit

   • A closed-loop path which a current take is called an electric circuit. Representation of an electric circuit through symbols is called a circuit diagram.

7. Resistance

   • Resistance is a measure of the opposition offered to the current flow in an electric circuit.
   • Resistance is: directly proportional to the length of the conductor. directly proportional to nature of the conductor. directly proportional to the temperature of the conductor. inversely proportional to the cross-sectional area of the conductor.

8. OHMs law

   • The current flowing through an ohmic conductor is directly proportional to the applied potential difference between the two ends of the conductor.

9. Resistivity

   • The electrical resistance offered by a substance of unit length and unit cross-sectional area is called resistivity.

10. Combination of resitors

    • Two resistors are said to be combined in series if they carry the same current. Two resistors are said to be combined in parallel if the same potential difference is applied to them.

11. Equivalent Resistance of a system of resistors

    • The equivalent resistance of two resistors is given as: In series, R e q = R 1 + R 2 In parallel, 1/ R e q = 1/ R 1 + 1/ R 2

12. Heating Effect of Current Joule's Law: Heat (H) ∝ square of the current (I). H ∝ Resistance of the given circuit. H ∝ Time (t) for which current flows through the conductor.

13. Electric Power The rate of doing work or rate of consumption of electrical energy is called Electric Power. If W is work done in time t, then P = W/ t .