Class 10 Science • Chapter 13 • Complete Notes
A magnetic field is the region around a magnet or a current-carrying conductor in which a magnetic force can be experienced.
A current-carrying conductor produces a magnetic field around itself. This is one of the most important ideas in the chapter.
Magnetic field lines are imaginary lines used to represent a magnetic field graphically.
When electric current passes through a straight conductor, a magnetic field is produced around the conductor.
The magnetic field lines around a long straight current-carrying conductor are concentric circles whose centre lies on the conductor.
Increasing the current increases the strength of the magnetic field.
The magnetic field becomes weaker as the distance from the conductor increases.
The right-hand thumb rule helps determine the direction of the magnetic field around a straight current-carrying conductor.
If a straight conductor is held in the right hand with the thumb pointing in the direction of current, the curled fingers show the direction of magnetic field lines.
When current flows through a circular loop, every small section of the loop contributes to the magnetic field. The combined effect produces a magnetic field pattern similar to that of a bar magnet.
At the centre of the circular loop, the magnetic field contributions from different portions reinforce one another.
For a given arrangement, increasing current or increasing the number of turns generally increases the magnetic field.
A solenoid is a long cylindrical coil containing many closely spaced turns of insulated wire.
When electric current passes through a solenoid, it produces a magnetic field. The field inside a sufficiently long solenoid is strong and approximately uniform in the central region.
A soft iron core placed inside a current-carrying solenoid can strongly increase its magnetic effect. Such an arrangement is called an electromagnet.
When a current-carrying conductor is placed in an external magnetic field, the conductor can experience a force.
The direction of the force depends on the directions of current and magnetic field.
The force is maximum when the conductor is perpendicular to the magnetic field.
Fleming's Left Hand Rule is used to find the direction of force acting on a current-carrying conductor placed in a magnetic field.
An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force.
A current-carrying coil placed in a magnetic field can rotate because the forces acting on opposite sides of the coil form a turning effect.
The split-ring commutator reverses the current direction in the coil after each half rotation, helping the coil continue rotating in the same overall direction.
Electromagnetic induction is the phenomenon in which an electric current is induced in a conductor when the magnetic conditions associated with the conductor change.
For example, moving a magnet relative to a coil can produce an induced current in the coil.
Fleming's Right Hand Rule is used to determine the direction of induced current in a moving conductor in a magnetic field.
An electric generator converts mechanical energy into electrical energy by electromagnetic induction.
An AC generator produces alternating current. The direction of the induced current changes periodically as the coil rotates.
A DC generator arrangement uses a split-ring commutator so that the external current is delivered in one direction.
| Feature | DC | AC |
|---|---|---|
| Direction | Essentially one direction | Periodically changes direction |
| Typical Source | Cells/Batteries | Alternating-current generators / mains supply |
Electrical energy is supplied to homes through domestic electric circuits. Safety devices are used to reduce risks from excessive current and faulty circuits.
A fuse is a protective device that melts and breaks the circuit when excessive current flows.
A short circuit provides an unintended low-resistance path that can cause a very large current to flow.
Overloading occurs when a circuit is made to carry more current than it is safely designed to handle.
| Concept | Meaning | Rule / Principle |
|---|---|---|
| Motor Effect | Force on current-carrying conductor in magnetic field | Fleming's Left Hand Rule |
| Electromagnetic Induction | Induced current due to changing magnetic conditions | Fleming's Right Hand Rule for direction |
| Electromagnet | Magnetic effect produced by current through a coil | Magnetic effect of current |
| Generator | Mechanical energy converted into electrical energy | Electromagnetic induction |