PHYSICS MP EXAM CRAM REVISION

Live Wire (Line Wire)

Brown insulation; carries the high alternating voltage into the appliance.

Neutral Wire

Blue insulation; completes the circuit loop by forming a return path held at approximately 0V.

Earth Wire

Green and yellow stripes; safety wire connecting the metal casing to the ground to safely divert fault currents.

Switch Connection Rule

Must always be connected to the live wire so that turning it off completely isolates the appliance from high voltage.

Fuse Operation

Contains a thin wire on the live line that melts and breaks the circuit if the current exceeds its specific rating.

Trip Switch (Circuit Breaker)

Uses an electromagnet to automatically snap open a switch during an overcurrent; easily reset without replacement.

Choosing a Fuse Rating

Must be selected to be just above the normal operating current of the appliance.

Double Insulation

Used for appliances with non-conducting plastic casings; prevents shocks without needing an earth wire.

Kilowatt-Hour (kWh)

A unit of energy equal to the energy transferred by a 1 kW appliance running continuously for 1 hour (equals 3.6 x 10^6 Joules).

Energy Cost Formula

Total Cost = Power (kW) x Time (hours) x Cost per kWh.

Parallel Resistance Rule

The combined resistance of two resistors connected in parallel is always less than the resistance of either individual resistor.

Potential Divider

A series circuit configuration that splits the supply voltage across resistors in proportion to their resistance values.

LDR Resistance Behavior

Resistance decreases as light intensity increases (Light Up, Resistance Down).

Thermistor Resistance Behavior

Resistance decreases as temperature increases (Temperature Up, Resistance Down).

Ionisation

The process where a neutral atom becomes a charged ion by either gaining or losing electrons.

Proton Number (Z)

The total number of protons in a nucleus; determines the element's identity and positive nuclear charge.

Nucleon Number (A)

The total number of protons plus neutrons in a nucleus; determines its relative mass.

Isotopes

Atoms of the same element containing the same number of protons but a different number of neutrons.

Nuclear Fission

The splitting of a massive, unstable nucleus into two lighter daughter nuclei, releasing neutrons and large amounts of energy.

Nuclear Fusion

The joining of two light, fast-moving nuclei to form a single heavier nucleus, releasing massive energy (powers stars).

Background Radiation

Low-level ionising radiation present around us at all times from natural sources (radon, rocks, cosmic rays) and artificial sources.

Radioactive Decay Nature

A spontaneous process (unaffected by external factors like temperature) and random process (unpredictable exactly when a nucleus decays).

Alpha Particle

A helium nucleus (2 protons, 2 neutrons); highly ionising, very weakly penetrating (stopped by paper or a few cm of air).

Beta Particle

A fast-moving electron; moderately ionising, moderately penetrating (stopped by a few mm of aluminum).

Gamma Ray

High-energy electromagnetic wave; extremely weakly ionising, highly penetrating (reduced only by thick lead or concrete).

Beta Decay Mechanism

An excess neutron inside an unstable nucleus spontaneously converts into a proton (stays in nucleus) and an electron (ejected).

Alpha Decay Change

Nucleus loses 4 from its mass number (A) and 2 from its proton number (Z).

Beta Decay Change

Nucleus mass number (A) remains unchanged, while its proton number (Z) increases by 1.

Half-Life

The time taken for exactly half of the unstable nuclei in a sample to decay, or for its activity/count rate to drop by half.

Three Pillars of Radiation Safety

Minimise Time near the source, Maximise Distance from the source, and use appropriate Shielding (like lead).

Refraction

The bending of light as it passes between media of different optical densities due to a change in wave speed.

Refraction Direction (Less to More Dense)

Light slows down and bends towards the normal.

Refraction Direction (More to Less Dense)

Light speeds up and bends away from the normal.

Refractive Index (n)

The ratio of the speed of light in a vacuum to the speed of light in a medium (n = c / v or n = sin i / sin r).

Critical Angle

The specific angle of incidence in the optically denser medium that results in an angle of refraction of exactly 90 degrees.

Total Internal Reflection (TIR) Conditions

1. Light must travel from a denser to a less dense medium. 2. The angle of incidence must be greater than the critical angle.

Virtual Image

An image formed where diverging light rays appear to come from when extrapolated backwards; cannot be projected onto a screen.

Magnifying Glass Action

A converging lens where the object is placed inside the focal length, producing a virtual, upright, and magnified image.

Wavefront

An imaginary line connecting neighboring points on a wave that are in phase, such as along a wave crest.

Diffraction

The spreading out of waves as they pass through a gap or past the edge of an obstacle.

Maximum Diffraction Condition

Occurs when the physical width of the gap is approximately equal to the wavelength of the wave.

Dispersion of Light

The splitting of white light into its component colors (ROYGBIV) because different wavelengths slow down and refract by different amounts in a prism.

Monochromatic Light

Light consisting of a single frequency or a single wavelength (e.g., a pure laser beam).

Speed of EM Waves

All electromagnetic waves are transverse and travel at a universal constant speed of 3.0 x 10^8 m/s in a vacuum.

Electromagnetic Spectrum Order

Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma ray (ordered from lowest to highest frequency).

Microwave Uses & Hazards

Satellite links, mobile phones, Wi-Fi, cooking. Hazard: Internal heating of body cells.

Infrared Uses & Hazards

Remotes, thermal imaging, optical fibres. Hazard: Skin burns.

Ultraviolet Uses & Hazards

Security marking, sterilising water. Hazard: Damage to surface cells/eyes, cataracts, skin cancer.

X-Rays & Gamma Rays Hazards

Severe cell mutations, deep tissue damage, and cancer.

Analogue Signal

A continuously variable signal that can take any value within a given range.

Digital Signal

A discrete signal existing in only two distinct states: high/on (1) or low/off (0).

Benefits of Digital Signalling

Allows higher data transmission rates, covers longer ranges, and noise can be completely removed during amplification.

Scalar Quantity

A quantity possessing magnitude (size) only (e.g., distance, speed, mass, energy, time).

Vector Quantity

A quantity possessing both magnitude and direction (e.g., force, weight, velocity, acceleration, momentum).

Terminal Velocity Process

Object drops and accelerates due to weight; speed rises causing air resistance to rise; drag eventually equals weight, making net force and acceleration zero.

Solid Friction

A resistive force acting between two solid surfaces in contact that opposes relative motion and generates thermal energy.

Motion in a Circular Path

Object moves at constant speed but changes direction continuously, meaning it is accelerating and requires a net centripetal force directed toward the center.

Absolute Zero

Defined as -273 degrees Celsius; the theoretical point where particles possess minimum kinetic energy and all molecular motion stops.

Gas Pressure Cause

The rapid, random motion of gas particles colliding with the internal walls of their container, exerting a net force over an area.

Brownian Motion

The erratic, random motion of microscopic particles (like smoke) caused by continuous, random bombardment by fast-moving invisible fluid molecules.

Evaporation vs Boiling

Evaporation happens at any temperature, only at the surface, and cools the liquid. Boiling happens at a fixed point throughout the entire bulk liquid.

Thermal Conduction in Metals

Enhanced by fast-moving free (delocalised) electrons that absorb energy and rapidly drift through the structure, colliding with distant ions.

Convection Mechanism

Fluid is heated, expands, becomes less dense and rises, while cooler, denser fluid sinks to replace it, creating a current.

Thermal Radiation Surfaces

Matt black surfaces are the best absorbers and emitters. Shiny silver/white surfaces are the worst absorbers (best reflectors) and worst emitters.

Electric Field

A region of space in which a stationary electric charge experiences a non-contact electric force.

Electric Field Line Direction

The direction of the force that acts on a positive charge (directed away from positive charges and towards negative charges).

Electromagnetic Induction

The generation of an electromotive force (e.m.f.) across a conductor when it cuts magnetic field lines or experiences a changing magnetic field.

Lenz's Law

The direction of an induced e.m.f. or current always acts to oppose the magnetic change that is causing it.

Factors Increasing Induced e.m.f.

Moving the conductor/magnet faster, using a stronger magnet, or increasing the number of turns in the wire coil.

AC Generator Max e.m.f. Position

Occurs when the rotating coil is moving parallel to the magnetic field lines, cutting across them at the maximum possible rate.

AC Generator Zero e.m.f. Position

Occurs when the rotating coil is moving perpendicular to the magnetic field lines, momentarily cutting zero lines per second.