CBSE Class 10 Science Chapter 13 Revision Notes

Chapter 13: Magnetic Effects of Electric Current

Field and Field Lines

• A magnet is a substance that creates a magnetic field that attracts or repels other magnetic materials.
• Lodestone is a type of magnet that occurs naturally. It attracts metals such as iron, nickel, and cobalt, among others.

North and South Poles

• A bipolar magnet is always bipolar, possessing north and south poles.
• These two poles are inextricably linked and cannot be separated.
• When a magnet is freely hanging, its north pole is the side that faces Earth’s geographic north.

Like poles repel and unlike poles attract

• Poles attract and repel in the same way as charges do.
• Poles that are similar repel each other, whereas poles that are dissimilar attract each other.

Bar magnet

• A bar magnet is a rectangular item with permanent magnetic qualities made of iron, steel, or any other ferromagnetic material.
• It has two poles, one north and one south, and when hanging freely, the north pole aligns itself with the Earth’s geographic north pole.

Magnetic field

• A magnetic field is the region around a magnet where its magnetic effect may be felt. Magnetic lines of force represent the direction and strength of a magnetic field.
• A bar magnet is used to test iron filings.
• The magnetic field lines that round a bar magnet are seen in the iron filings that surround it. Magnetic field lines can be thought of as fictitious lines that visually illustrate the magnetic field that surrounds any magnetic material.

Lines of magnetic field

• Magnetic field lines produce continuous/running closed loops as a result of the magnet’s magnetic field lines.
• The direction of the total magnetic field at any given position is shown by the tangent to the field line.
• The magnitude of the magnetic field is proportional to the number of field lines crossing per unit area. The bigger the number of field lines crossing per unit area, the higher the intensity.
• There is no point where the magnetic field lines cross.
• Lines of magnetic field for a closed loop
• Magnetic field lines must begin and terminate because magnets contain dipoles. As a result, it starts at the north pole and goes south outside the bar magnet, then from south to north inside the magnet, according to convention. As a result, it creates closed loops.
• There are no magnetic field lines that cross one other.
• Magnetic field lines do not cross because two tangential magnetic field directions would be linked with the same location, which is not the case. When a compass needle is positioned at that location, it shows two separate magnetic field directions, which is nonsensical.
• Magnetic field lines indicate the relative intensity of the magnetic field.
• The magnetic field’s intensity increases as the magnetic field lines become closer or denser.

MAGNETIC FIELD DUE TO CURRENT CARRYING CONDUCTORS

Oersted’s experiment

• A magnetic field is created when electric current travels through a current carrying conductor.
• A magnetic needle that demonstrates deflection can be used to demonstrate this. The deflection increases as the current increases.
• When the current is reversed, the direction of deflection is reversed as well.

Electromagnetism and electromagnet

• An electromagnet is a man-made magnet that generates a magnetic field when an electric current passes through a conductor.
• When the current is switched off, this field vanishes.
• Electromagnetism is the phenomena of creating or inducing a magnetic field as a result of the passage of an electric current.

Magnetic field due to a straight current carrying conductor

• A magnetic field is created around a straight current-carrying conductor when electricity is transmitted through it.
• We can see that the iron filings organise themselves in concentric circles around the conductor when we use them.

Right-hand thumb rule

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• When a straight conductor is held in the right hand with the thumb pointing in the direction of the current, the tips or curls of the fingers indicate the direction of the magnetic field surrounding it.
• Current across a circular loop produces a magnetic field.
• A circular conducting wire with tiny straight segments may be measured using the right-hand thumb rule.
• Every point on the current-carrying wire generates a magnetic field in the centre, which appears as straight lines.

Magnetic field due to current in a solenoid

• A solenoid is a cylinder-shaped coil made up of several circular windings.
• When current is run through it, it acts like a bar magnet, creating a field pattern that is extremely similar to that of a bar magnet.
• A soft iron core is employed to boost the strength.

Ampere’s experiment

• An electric conductor is subjected to a force when it is put in a magnetic field.
• This force is proportional to the current and perpendicular to the length and magnetic field of the current.

Fleming’s left-hand rule

• The direction of force applied to a current carrying wire must be perpendicular to both the current direction and the magnetic field, according to Fleming’s left hand rule.

Electric motor

• Electrical energy is converted into mechanical energy by an electric motor.
• Brush X allows current to enter arm AB, while brush Y allows current to travel from C to D. We can see that the force pulls AB downwards and CD upwards using Fleming’s LHR.
• The split rings PQ operate as a commutator in an electric motor, reversing the current direction. The current reversal is repeated every half rotation, resulting in a continuous rotation of the coil.

ELECTROMAGNETIC INDUCTION AND ELECTRIC GENERATOR

Faraday’s experiment

• By electromagnetic induction, Faraday showed that a magnetic field interacts with an electric circuit by generating a voltage known as EMF (electromotive force).
• A current is established in the coil circuit when a magnet is moved towards it, as shown by a deflection in the galvanometer needle.

Electromagnetic induction

• The formation of induced EMF and hence current in a coil owing to a shifting magnetic field over time is known as electromagnetic induction.
• The magnetic field changes when a coil is put near a current-carrying conductor owing to a change in I or relative motion between the coil and conductor.
• Fleming’s right-hand rule determines the direction of the induced current.

Fleming’s right-hand rule

• The thumb, forefinger, and middle finger of the right hand are extended perpendicular to each other according to Fleming’s right-hand rule, as seen below.
• If the thumb points in the direction of conductor movement, the forefinger points in the direction of the magnetic field, and the middle finger points in the direction of the induced current, then the middle finger points in the direction of the induced current.

Electric generator

• Mechanical energy is converted into electrical energy by this gadget.
• The principle of operation is electromagnetic induction.
• The axle connecting to the two rings is rotated, causing the arms AB and CD to move up and down in the created magnetic field, respectively. As a result, the induced current is directed through ABCD.
• The direction of current in both arms changes after half revolution. The induced currents are created in these arms along directions DC and BA, again using Fleming’s right hand rule, so the induced I flows through DCBA.
• DC Generators: They function similarly to AC generators, but instead employ half rings to create current in a single direction with no magnitude fluctuations.

DOMESTIC ELECTRIC CIRCUITS

Fuse

• In the event of an electrical circuit overloading, a fuse serves as a protection measure.
• When the neutral and live wires come into touch owing to insulation damage or a line failure, overloading occurs.
• When the circuit is overloaded, the current in the circuit rises (short circuit) and becomes dangerous. The fuse device melts the circuit and interrupts current flow due to Joule heating (resistive or ohmic heating on current passage).
• The voltage of the livewire is 220 V, and it is insulated with red insulation.
• The earth line is wrapped in green insulation and has a voltage of 0 V (the same as Earth).
• The neutral wire is insulated with black insulation.
• We have 220 V AC electric electricity at a frequency of 50 Hz in our homes.

Transmission loss of power

• Joule’s heating causes power losses in transmission cables over long distances. Losses are caused by the heat (H) l2R, where R is the line resistance.

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