Physics definitions

Faraday’s law

… Law of Electromagnetic Induction states that the induced electromotive force (EMF) in a circuit is directly proportional to the rate of change of magnetic flux through the circuit.

If the magnetic field through a coil changes—either by varying the field strength, the area of the loop, or the angle—the coil experiences an induced voltage (EMF), which can drive an electric current if a closed circuit is present.

Lenz’s law

states that the direction of the induced current in a conductor is always such that it opposes the change in magnetic flux that caused it.

• If the magnetic flux through a loop increases, the induced current will flow in a direction that creates a magnetic field opposing this increase.

• If the flux decreases, the induced current will generate a field that tries to maintain it.

Key Idea: Conservation of Energy

… Law ensures that energy is conserved by opposing the change that produces the induced current.

Coulomb’s law

states that the electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Key Points:

• If the charges have the same sign (+/++/+ or −/−−/−), the force is repulsive.

• If the charges have opposite signs (+/−+/−), the force is attractive.

• The force follows an inverse square law, meaning that if the distance doubles, the force becomes one-fourth as strong.

Equipotential lines

Definition:

Equipotential lines (or equipotential surfaces in 3D) are imaginary lines in an electric field where every point has the same electric potential. This means that no work is required to move a charge along an equipotential line because the electric potential remains constant.

Key Properties:

1. Always Perpendicular to Electric Field Lines

   • Electric field lines show the direction of force on a positive charge, while equipotential lines are always at right angles to these field lines.

   • This ensures that no work is done when moving a charge along an equipotential line.

2. Closer Equipotential Lines Indicate Stronger Fields

   • When equipotential lines are closer together, the electric field is stronger.

   • When they are farther apart, the field is weaker.

3. No Work Done Along Equipotential Lines

   • Since the potential remains the same, moving a charge along an equipotential surface does not require energy.

4. Examples in Different Fields:

   • Uniform Electric Field: Equipotential lines are equally spaced, straight, and parallel.

   • Point Charge: Equipotential lines are concentric circles (or spheres in 3D) centered around the charge.

   • Dipole: Equipotential lines form complex curved shapes around the positive and negative charges.

Applications:

• Electrical circuits: Helps in designing capacitors and insulators.

• Geophysics: Used to map gravitational and electric potentials.

• Medical applications: Helps in electrocardiograms (ECGs) and brain activity mapping.

Internal energy

Total potential energy and random kinetic energy of all the particles in a substance.

Boyle’s law

For a fixed mass of gas at constant temperature the pressure is inversely proportional to the volume. PV = constant

Travelling waves

Transfer energy from one place to another as it moves.

Standing waves

Formation:

Do not transfer energy

Mechanical waves

Require a medium to travel in

Electromagnetic waves

Do not require a medium and can travel in a vacuum.

Longitudinal waves

Direction of energy is parallel to the motion of the particles.

Rarefactions and compressions.

Sound waves

Transverse waves

Motion of particles is perpendicular to the energy transfer.

Crests and troughs

Light waves/EM waves

Gravitational potential energy

Ep

Work done against gravity to assemble the system from an infinite separation of the components.

Gravitational potential

Vg

Work done per unit mass in bringing an object from infinity.