- Electric energy from a cell is used to do work on charges, which is converted into heat in a resistor or other forms, like motion in a motor.
- The work done (energy) in moving a charge Q across a potential difference VAB is:
Work = VAB × Q - Heat produced (H) in a resistor over time t is given by Joule’s Law of Heating:
H = I2 × R × t - According to Ohm’s Law:
VAB = I × R - Electrical power (P) is the rate of energy transfer and is calculated as:
P = VAB × I
Its unit is watt (W), where 1W = 1 volt × 1 ampere.
Definitions [8]
Definition: Switch
A switch is an on-off device for current in a circuit (or in an appliance). It is connected in the live wire.
Definition: Semiconductors
The material with electrical conductivity between that of a conductor and an insulator, whose number of charge carriers can be controlled as per requirement, is called a semiconductor. (e.g. Silicon, Germanium)
Definition: Energy Bands
The different energy levels with continuous energy variation are called energy bands.
Definition: Valence Band
The range of energies possessed by valence electrons is called valence band.
Definition: Conduction Band
The range of energies possessed by conduction electrons is called conduction band.
Definition: Forbidden Energy Gap
The energy difference between the valence band and the conduction band is called forbidden energy gap.
Definition: Conductors
The solids which have a large number of free electrons are called conductors. (e.g. Iron, Aluminium)
Definition: Insulators
The solids which have very small number of free electrons are called insulators. (e.g. Glass, Wood)
Key Points
Key Points: Electric Circuit
Key Points: Energy Bands in Solids
- Conductors → Eg = 0 - bands overlap, electrons flow freely.
- Semiconductors → Eg < 3 eV — small gap, conducts at room temperature.
- Insulators → Eg > 5 eV — large gap, no conduction.
- Ge = 0.72 eV, Si = 1.1 eV — both semiconductors.
- Metal conductivity decreases with temp. Semiconductor conductivity increases with temp.
