Electromagnetism

Magnetic poles always exist in pairs, known as north and south poles. Unlike poles attract each other, and like poles repel each other. A single magnetic pole, or monopole, has never been observed.

Inside a bar magnet, magnetic field lines are directed from the south pole to the north pole.

A magnetic compass aligns itself with the magnetic field, making it a useful tool for detecting the presence of a magnetic field.

When a current-carrying wire is placed perpendicular to a magnetic field, the force on the wire increases according to the formula \( F = ILB \), where \( I \) is the current, \( L \) is the length of the wire, and \( B \) is the magnetic field strength.

A D.C motor converts electrical energy into mechanical energy, which is used to perform mechanical work.

The commutator in a D.C motor reverses the direction of current through the coil every half-cycle, ensuring continuous rotation.

The direction of induced e.m.f. in a circuit is determined by Lenz's law, which is in accordance with the conservation of energy.

A step-up transformer increases the input voltage. It has more turns in the secondary coil compared to the primary coil.

A turn ratio of 10 means that the secondary coil has 10 times the number of turns as the primary coil (\( Ns = 10 Np \)).

The force acting between charged particles is the electromagnetic force, which includes both electric and magnetic forces.

The right thumb rule (or right-hand grip rule) is used to determine the direction of the magnetic field around a current-carrying wire.

The region where the influence of magnetism is felt is called a magnetic field.

The magnetic field is strongest near the poles of a magnet.

When a magnetic field around a current-carrying wire interacts with an external magnetic field, a force is exerted on the wire due to the interaction of the two magnetic fields.

The force on a current-carrying wire in a magnetic field is given by \( F = IL \times B \), where \( I \) is the current, \( L \) is the length of the wire, and \( B \) is the magnetic field.

The main function of a DC motor is to convert electrical energy into mechanical energy.

Faraday observed that a voltage (emf) and current were produced when a magnet was moved in and out of a coil, demonstrating electromagnetic induction.

The torque on a current-carrying coil in a magnetic field is given by \( \tau = NIAB \sin \theta \), where \( N \) is the number of turns, \( I \) is the current, \( A \) is the area of the coil, \( B \) is the magnetic field, and \( \theta \) is the angle between the magnetic field and the normal to the coil.

Dynamically induced emf is the emf produced when a conductor moves in a magnetic field, which is a fundamental principle of electromagnetic induction.

Statically induced emf occurs when the magnetic field changes but the conductor remains stationary, which is another aspect of electromagnetic induction.

Eddy currents are currents induced in metals due to changing magnetic fields, which can cause heating in the metal.

The function of a generator is to convert mechanical energy into electrical energy using the principle of electromagnetic induction.

A transformer works on the principle of mutual induction, where a changing magnetic field in one coil induces an emf in another coil.

The electromagnetic force is responsible for holding electrons around the nucleus of an atom.

When a magnetic field is changed near a conductor, an electric current is generated due to electromagnetic induction.

The unit of magnetic flux density in the MKS system is Tesla.

Like charges repel each other when brought near each other due to the electromagnetic force.

Frictional force is not one of the four fundamental forces of nature. The four fundamental forces are gravity, electromagnetism, the strong nuclear force, and the weak nuclear force.

Outside a bar magnet, the direction of magnetic field lines is from the north pole to the south pole.

The right-hand rule is used for determining the direction of the magnetic field around a current-carrying conductor.

When electrons move through a conductor, a magnetic field is created around the conductor.

The force on a moving charged particle in a magnetic field is given by \( F = qV \times B \), where \( q \) is the charge, \( V \) is the velocity, and \( B \) is the magnetic field.

When a charged particle is stationary, it creates an electric field around it.

The magnetic field is strongest near the poles of a magnet.

The formula for the force on a current-carrying conductor in a magnetic field is \( F = BIL \sin \theta \), where \( B \) is the magnetic field, \( I \) is the current, \( L \) is the length of the conductor, and \( \theta \) is the angle between the conductor and the magnetic field.

The direction of the force acting on a current-carrying conductor placed in a magnetic field is perpendicular to both the current and the magnetic field.

Placing the conductor perpendicular to the magnetic field increases the force on a current-carrying conductor in a magnetic field.

The unit of magnetic field 'B' in SI units is Tesla.

The force on the wire can be calculated using the formula \( F = BIL \sin \theta \). Given \( B = 1.50 \, \text{T} \), \( I = 20 \, \text{A} \), \( L = 0.05 \, \text{m} \), and \( \theta = 90^\circ \), the force is \( F = 1.50 \times 20 \times 0.05 \times \sin(90^\circ) = 1.50 \, \text{N} \).

A current-carrying coil rotates when placed in a magnetic field due to a pair of equal and opposite forces acting on the coil, which create a torque.

The torque on a current-carrying coil in a magnetic field is maximum when the magnetic moment is perpendicular to the magnetic field.

The formula for the torque on a current-carrying coil placed in a magnetic field at an angle \( \alpha \) is \( \tau = BIAN \cos \alpha \), where \( B \) is the magnetic field, \( I \) is the current, \( A \) is the area of the coil, \( N \) is the number of turns, and \( \alpha \) is the angle between the magnetic moment and the magnetic field.

The number of turns \( N \) in the coil increases the torque proportionally, as the torque is directly proportional to the number of turns.

When the plane of the coil is parallel to the magnetic field, no torque acts on the coil because the angle \( \alpha \) is \( 90^\circ \) and \( \cos(90^\circ) = 0 \).

The main function of a D.C motor is to convert electrical energy into mechanical energy.

A D.C motor is constructionally similar to a D.C generator, as both involve coils, commutators, and brushes.

When a magnet is moved towards a coil, the galvanometer needle deflects in one direction due to the induced current in the coil.

According to Faraday's law, the induced e.m.f. is proportional to the rate of change of magnetic flux through the coil.

According to Lenz's law, the direction of the induced current is such that it opposes the change that caused it, which is a consequence of the conservation of energy.

Lenz's law supports the law of conservation of energy by ensuring that the induced current opposes the change in magnetic flux.

If a coil is moved away from a magnet, the galvanometer needle deflects in the opposite direction due to the change in the direction of the induced current.

When the plane of the coil is parallel to the magnetic field, no e.m.f. is induced because the magnetic flux through the coil does not change.

The main function of an AC generator is to convert mechanical energy into electrical energy using electromagnetic induction.

An AC generator works on the principle of electromagnetic induction, where a changing magnetic field induces an electric current in a conductor.

In an AC generator, the wire coil rotates in a magnetic field to produce electricity through electromagnetic induction.

Carbon brushes in an AC generator maintain electrical contact with the rotating coil, allowing the induced current to flow to the external circuit.

Mutual induction occurs when a changing current in one coil induces an electromotive force (e.m.f.) in another nearby coil due to the changing magnetic field.

An e.m.f. is induced in the secondary coil during mutual induction due to the changing magnetic flux caused by a varying current in the primary coil.

The e.m.f. induced in the secondary coil is proportional to the rate of change of current in the primary coil.

The S.I. unit of mutual inductance is Henry (H).

One Henry is equal to one Volt-Second per Ampere (V·s/A).

A transformer operates on the principle of mutual induction, where a changing current in the primary coil induces an e.m.f. in the secondary coil.

When current flows through the primary coil of a transformer, a magnetic field is created, which induces an electromotive force (EMF) in the secondary coil due to mutual induction.

In a step-up transformer, the secondary voltage is greater than the primary voltage. This is achieved by having more turns in the secondary coil than in the primary coil.

Mobile chargers use step-down transformers to reduce the high voltage from the mains supply to a lower voltage suitable for charging mobile devices.

In an ideal transformer, the power in the primary coil is equal to the power in the secondary coil, assuming no losses. This is based on the principle of conservation of energy.

The mathematical expression of power equality in an ideal transformer is \( V_p I_p = V_s I_s \), where \( V_p \) and \( I_p \) are the voltage and current in the primary coil, and \( V_s \) and \( I_s \) are the voltage and current in the secondary coil.

A transformer in a circuit breaker helps prevent damage from high voltage currents by stepping down the voltage to safer levels, protecting the electrical devices and circuits.