Physics — Electricity & Magnetism

Tungsten is used because it has an extremely high melting point (approx 3422°C), allowing it to glow without melting.

Inside a magnet, magnetic field lines run from the South pole to the North pole, forming continuous closed loops.

Resistivity (ρ) is defined by the formula R = ρ(L/A), which gives the SI unit as Ohm-meter (Ω·m).

A fuse is a safety device connected in series with the live wire so that if current exceeds the limit, the circuit breaks.

Michael Faraday discovered electromagnetic induction in 1831, proving that a changing magnetic field induces an electromotive force (EMF).

An electric generator works on the principle of electromagnetic induction to convert mechanical energy into electrical energy.

The force F = BIL sin(θ). The force is maximum when sin(θ) is 1, which occurs at 90 degrees.

A step-down transformer is designed to decrease the voltage of an alternating current (AC) while increasing the current.

A diode is a non-ohmic conductor because it does not follow Ohm's Law (the current-voltage graph is not a straight line).

Oersted observed that a compass needle deflects when placed near a wire carrying an electric current, establishing the link between electricity and magnetism.

In series, resistors are added directly: R_total = R1 + R2 = 2 + 4 = 6 ohms.

Silver is the best conductor of electricity among all metals, meaning it has the lowest resistivity.

Lenz's Law, which states that induced current opposes the change in magnetic flux, is a direct consequence of the law of conservation of energy.

An ammeter is a measuring instrument used to measure the electric current in a circuit and is always connected in series.

Fleming's Left-Hand Rule states that the thumb, index finger, and middle finger are kept mutually perpendicular to each other.

Superconductivity is a state where a material exhibits zero electrical resistance when cooled below a specific 'critical temperature'.

In India, the power supply provided to residential and commercial consumers is Alternating Current (AC) at 50 Hz frequency.

The earth wire is connected to the metal body of an appliance to conduct any leakage current safely to the ground, preventing electric shocks.

Soft iron is used for electromagnets because it has high permeability and low retentivity, meaning it is easily magnetized and demagnetized.

Faraday's Law of Electromagnetic Induction dictates that a time-varying magnetic field induces an electromotive force.

The magnetic field at the center of a circular loop is inversely proportional to its radius (B = μ₀I / 2R); doubling R halves the magnetic field.

A capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field.

The Tesla (T) is the derived SI unit of magnetic induction or magnetic flux density.

Unlike metals, semiconductors have a negative temperature coefficient of resistance; higher temperatures release more charge carriers, increasing conductivity.

Diamagnetic materials like copper, water, and gold are weakly repelled by a magnetic field.

For n resistors of equal value R connected in parallel, the effective resistance is R/n. Here, 6/3 = 2 ohm.

A split-ring commutator acts as a reversing switch that maintains the rotation of the motor in the same direction.

An ideal ammeter should have zero resistance so that it does not alter the current in the branch it is measuring.

A transformer operates on the principle of mutual induction between two coils linked by a common magnetic flux.

Conventional current is defined as flowing from the positive terminal of a power source to the negative terminal.

Coulomb's Law states that the force between two point charges is proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.

Relative motion between a magnet and a coil induces an EMF/current due to the change in magnetic flux (Electromagnetic Induction).

Fleming's Right-Hand Rule: The thumb represents the direction of motion of the conductor relative to the magnetic field.

Devices like electric irons, heaters, and toasters work on the Joule heating effect (H = I²Rt).

Resistance is directly proportional to the length of the conductor (R = ρL/A).

Laminated cores are used to break the path of eddy currents, significantly reducing energy loss in the form of heat.

Soft iron is preferred for electromagnets because it magnetizes and demagnetizes easily.

In a parallel connection of identical batteries, the voltage remains the same as that of a single battery, though the current capacity increases.

Maxwell's equations are a set of partial differential equations that describe how electric and magnetic fields interact.

Superconductivity is a state of matter occurring in certain materials at very low temperatures, characterized by zero electrical resistance and the expulsion of magnetic fields.

A split-ring commutator acts as a reversing switch in a DC motor, ensuring the torque acts in the same direction to keep the coil rotating continuously.

Resistance is directly proportional to the length (R ∝ L). Thus, doubling the length doubles the resistance of the conductor.

Manganin is used because it has a very low temperature coefficient of resistance, meaning its resistance remains stable even if the temperature rises during current flow.

Ferromagnetic materials like Iron, Cobalt, and Nickel are strongly attracted by magnetic fields and can be permanently magnetized.

Laminating the core breaks the path for eddy currents, which are circulating currents induced in the metal, thereby significantly reducing energy loss as heat.

The Weber (Wb) is the SI unit of magnetic flux, whereas Tesla is the unit of magnetic flux density.

For resistors in parallel, 1/Rp = 1/R1 + 1/R2 + 1/R3. For identical resistors, Rp = R/n. Here, 9/3 = 3 ohm.

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

In the Right-Hand Rule, the thumb points in the direction of motion, the forefinger represents the magnetic field, and the middle finger represents the induced current.