Electricity
1. Positive and Negative Charges
Definition: The charge acquired by a glass rod when rubbed with silk is called positive charge,
while the charge acquired by an ebonite rod when rubbed with wool is called negative charge.
2. Coulomb (C)
SI Unit of Charge: One coulomb is defined as the amount of charge that repels an equal and
similar charge with a force of 9 × 109 N when placed in vacuum at a distance of 1 meter.
Charge on an electron: -1.6 × 10-19 C
3. Static and Current Electricity
Static electricity deals with electric charges at rest, while current electricity deals with electric charges in motion.
4. Conductor
A substance that allows electric charges to pass through it easily, offering very low resistance. Examples: Copper, Silver, Aluminium.
5. Insulator
A substance with infinitely high resistance that does not allow electric current to flow through it. Examples: Rubber, Glass, Plastic.
6. Electric Current
The flow of electric charges across a cross-section of a conductor.
Formula: I = Q/t (Electric Current = Charge/Time)
7. Ampere (A)
Definition: SI unit of current. One ampere is the current flowing through a conductor when one coulomb of charge passes in one second.
- 1 A = 1 C/s
- 1 milliampere = 1 mA = 10-3 A
- 1 microampere = 1 µA = 10-6 A
8. Electric Circuit
The closed path along which electric current flows.
9. Conventional Current
Defined as the direction of motion of positive charges, opposite to the direction of negatively charged electrons.
10. Electric Field
The region around a charged body within which its influence can be experienced.
11. Electrostatic Potential
Work done in bringing a unit positive charge from infinity to a point in an electric field.
12. Potential Difference
Work done in bringing a unit positive charge from one point to another.
Formula: V = W/Q
13. Ohm’s Law
The current passing through a conductor is directly proportional to the potential difference across its ends, provided the physical conditions remain unchanged.
Formula: V = RI
14. Resistance (R)
Opposition to the flow of current. Formula: R = V/I
15. Joule’s Law of Heating
Heat produced in a conductor is proportional to:
- The square of the current (I2)
- Resistance (R)
- Time (t)
Formula: H = I2Rt
16. Electrical Power
Rate at which electric energy is consumed. Formula: P = VI
17. Kilowatt Hour
The commercial unit of electrical energy. One kilowatt hour is the energy consumed by a 1000 W appliance in one hour.
Formula: 1 kWh = 3.6 × 106 J