The conductivity of a semiconductor increases with rise in temperature. When temperature increases, a large number of covalent bondsbreak. This produces a larger number of charge carriers. So current increases.

It consists of a tungsten filament (melting point 3380^oC) kept inside a glass bulb with inert gas maintained at low pressure and heated to incandescence by the current. Electric discharge lamps, electric welding and electric arc also utilize the heating effect of current.

Furnaces used to manufacture a large number of technologically important materials such as steel, silicon carbide, quartz, gallium arsenide, etc. To produce temperatures up to 1500°C, a molybdenum-nichrome wire wound on a silica tube is used. Carbon arc furnaces produce temperatures up to 3000^oC.

When current flows through a resistor, some of the electrical energy delivered to the resistor is converted into heat energy and it is dissipated. This heating effect of current is known as Joule's heating effect.

The bridge wire is soldered at the ends of the copper strips. Due to imperfect contact, some resistance, might be introduced at the contact. These are called end resistances. This error can be eliminated, if another set of readings are taken with P and Q interchanged and the average value of P is found.

Voltage rating refers AC RMS voltages. For a given bulb, if the voltage drop across the bulb is greater than voltage rating, the bulb will fuse.

The electrical power P is the rate at which the electrical potential energy is delivered
\(P=\cfrac { dW }{ dt } =\cfrac { d }{ dt } \left( V.dQ \right) =V\cfrac { dQ }{ dt } \)
Since the electric current \(I=\cfrac { dQ }{ dt } \).
So the equation (1) can be rewritten as P = VI
This expression gives the power delivered by the battery to any electrical system, where I is the current passing through it and V is the potential difference across it. The SI unit of electrical power is a watt.

The resistanct is defined as the ratio of potential difference across the given conductor to the current passing through the conductor.
\(R=\cfrac { V }{ I } \)

Seebeck effect is used in
(i) Thermoelectric generators that are used in power plants to convert heat in to electricity.
(ii) In automobiles as automotive thermoelectric generators for increasing fuel efficiency.
(iii) Thermocouples and Thermopile are used to measure the temperature difference between two objects

Peltier discovered that, when an electric current is passed through a circuit of a thermocouple heat is evolved at one junction and absorbed at the other junction. This is known as Peltier effect.

The emf of the cell is directly proportional to the balancing length.

It states that in a closed circuit the algebraic sum of the products of the current and resistance of each part of the circuit is equal to the total emf included in the circuit.

Electric power:
(i) The electric power P is the rate at which the electrical potential energy is delivered.
(ii) The electric power P is the rate at which the work is done.
\( P= \frac{d U}{d t} (or)= \frac{d W}{d t} (or)=VI(or)\frac{V^2}{R}\)
Unit: watt (W)
Electric energy:
(i) The electric energy is the product of power (P) and duration of the time (t) when electric energy is delivered.
(ii) E = Pt
Unit: watt-hour (Wh)

A superconductor is any material that can conduct electricity with no resistance. In most cases, materials such as metallic elements or compounds offer some resistance at room temperature, but offer less resistance at a temperature known as its critical temperature.