Electric charge:
The origin of electricity lies in electric charges.
Electric charge is one of the basic fundamental properties of all matter, like mass and volume. Coulomb is the unit of measurement for electric charge, and it is denoted as 'C'.
Any charge (q) must be an integral multiple (n) of the fundamental unit of electron charge (e).
Then, the formula is written as \(q\ =\ ne\)
\(e\ =\ 1.6×10^{−19}\ C\)
Electricity is a branch of physics that deals with the flow of electric charges through a conductor.
Electricity is classified into two parts.
They are,
- Static electricity - Deals with electric charges at rest
- Current electricity - Deals with electric charges at motion
An electric current is generated by the motion of electric charges (electrons) through any conductor like copper wire. Electric current or simply current is denoted by the symbol 'I'. It is the total amount of charges flowing in a cross-section of a conductor in unit time.
\(I\ =\ \frac{q}{t}\), where "q" is the charge and "t" is time
Electric current is a scalar quantity. The SI unit of the electric current is ampere (A).
Conventionally, the electric current's direction is opposite to the direction of negative charges (electrons).
Electric potential:
The electric potential at a point is defined as the amount of work done in moving a unit positive charge from infinity to that point against the electric force. It is measured in terms of volts (V).
The movement of the positive charges or protons constitutes the conventional current whereas, the movement of the negative charges or electrons constitutes the electron current.
Electric potential difference:
The electric potential difference between two points is defined as the amount of work done in moving a unit positive charge from one point to another point against the electric force.
\(V\ =\ \frac{W}{q}\), where "W" is the work done and "q" is charge
Compennets of elctric circuit:
| Component | Working | Symbol |
| Battery | Two or more cells connected together |  |
| Cell | converts chemical energy into electric energy |  |
| Conducting wire | Pathway for electric current |  |
| Ammeter | To measure electric current |  |
| Voltmeter | To measure the potential |  |
| Resistor | Controlor regulate the current flow |  |
| Switch | stops or allows the current flow | |
| Rehostat | controls and selects the amount of current |  |
Ohm's law:
At a constant temperature, the steady current 'I' flowing through a conductor is directly proportional to the potential difference 'V' between the two ends of the conductor.
\(R\ =\ \frac{V}{I}\), Where "R" is resistance, "V" is volt and "I" is current.
The SI unit of resistance is ohm \(\Omega\)
The relation between potential difference and current
Conductors - The materials which allow the electric current to pass through them.
Insulators - The materials which do not allow the electric current to pass through them.
The resistance of a material or a conductor depends on three factors.
They are,
- Nature of conductor
- Length of conductor
- Area of a cross-section of the conductor
Electrical resistivity:
The electrical resistivity of a material is defined as the resistance of a conductor of unit length and unit area of cross-section.
The constant of proportionality is given as \(\rho\) in the above equation. It is known as an electrical resistivity or specific resistance of the material of the conductor.
The realtion between resistance, conductance, resistivity and conductivity is given as,
| Resistance | \(R\) | \(ohm\) | \(\Omega\) |
| Conductance | \(\frac{1}{R}\) | \(ohm^{-1}\) | \(\Omega^{-1}\) |
| Resistivity | \(\rho\) | \(ohm m\) | \(\Omega\ m\) |
| Conductivity | \(\frac{1}{\rho}\) | \(ohm^{-1}m^{-1}\) | \(\Omega^{-1}\) \(m^{-1}\) |
System of resistors:
A system of resistors is a combination or a group of resistors in a circuit.
Resistance in series - \(R_s\ =\ R_1\ +\ R_2\ +\ R_3\)
Resistance in parallel - \(\frac{1}{R_{eq}}\ = \frac{1}{R_1}\ +\ \frac{1}{R_2}\ +\ \frac{1}{R_3}\)
Joule' s law of heating:
The conversion of electrical energy into heat energy is known as Joule's heating.
\(H\ =\ I^2RT\), where I is current, R is resistance, T is time
The unit is Joule (J)
The heating appliances should have following properties
- It has high resistivity.
- It has a high melting point.
- It is not easily oxidised.
Fuse:
The fuse consists of a ceramic or porcelain body and two points for connecting the fuse wire. The fuse wire is made of a metal or an alloy containing 50% lead and 50% tin. The fuse wire can also be made with materials like aluminium, copper, iron, etc. Some properties of fuse wire are listed below.
- It has a high resistivity.
- It has a low melting point.
Electric Power:
Electric power is defined as the rate of doing work or spending energy. In other words, it is the rate of consumption of electrical energy.
\(P\ =\ VI\)
\(P\ =\ I^2R\)
\(P\ =\ \frac{V^2}{R}\)
The unit is Watt, \(W\)
Electrical energy:
The product of electric power and its usage time is used to calculate the electrical energy consumed.
\(Electrical\ energy\ =\ power\ \times\ time\)
The unit is \(watt hour\)
\(1\ watt\ hour\ =\ 3600 J\)
\(1\ kilo\ watt\ hour\ =\ 3.6\ \times\ 10^6\ J\)