- 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 [20]
Define the following term regarding a bar magnet:
Effective length
The distance (NS) between the north pole and south pole of a magnet is called the length or effective length of the magnet.
Define the terms magnet and magnetism.
The substances which have the property of attracting small pieces of iron, nickel, cobalt, etc, are called magnets, and this property of attraction is called magnetism.
Define the following term regarding a bar magnet:
Magnetic equator
An imaginary line (PQ) bisecting the effective length of a magnet is called the magnetic equator of the magnet.
Define the following term regarding a bar magnet:
Magnetic axis
An imaginary line (XY) passing through the magnetic north pole and magnetic south pole of a bar magnet is called its magnetic axis.
Define the following term:
Angle of dip
The angle between the horizontal and earth’s magnetic field is known as the angle of dip.
Define natural magnet.
It is a piece of lodestone, which is a black iron oxide (Fe3 O4) called magnetite. The word lodestone means a leading stone.
Define the following term regarding a bar magnet:
Magnetic field
The region around a magnet where its magnetic force can be experienced is called the magnetic field.
Define artificial magnet.
Pieces of iron and other magnetic materials which can be made to acquire the properties of natural magnets are called artificial magnets.
Define electromagnet.
lt is a solenoid with a soft iron core placed inside it. When current is passed through the solenoid, the soft iron core becomes a temporary magnet.
Define magnetic shielding.
The process of stopping the magnetic field from entering a region is called magnetic shielding.
Define magnetic flux density.
The number of magnetic field lines crossing unit area kept normal to the direction of field lines is called magnetic flux density. Its unit is Wb/m2
Definition: Electromagnet
An electromagnet is a temporary strong magnet made by passing current in a coil wound around a piece of soft iron. It is an artificial magnet.
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)
Define the term current.
An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire.
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.
Concepts [22]
- Magnet
- Discovery of Magnets
- Classification of Magnets
- Magnetic Properties of Materials
- Laws of Magnetism
- Magnetic Field
- Electromagnet
- Making of an Electromagnet
- Uses of Electromagnet
- Electric Bell
- Earth’s Magnetic Declination
- Electricity
- Sources of Electricity
- Electric Circuit
- Electrical Conduction in Solids
- Analogy of Electric Current with Water Flow
- Flow of Charges (Electrons) Between Conductor
- Symbols and Functions of Various Components of an Electric Circuits
- Types of Circuits: Series Circuit
- Types of Circuits: Parallel Circuit
- Electric cell
- Battery
