Revision notes: O Level Physics 6091 (Vocabulary Flashcards)

A comprehensive set of vocabulary flashcards covering key concepts, terms, and definitions from the provided O Level Physics 6091 revision notes. Useful for quick memorization of core ideas across measurement, mechanics, energy, waves, and electricity & magnetism.

Physical quantity

A quantity that has magnitude and a unit (e.g., 5.20 m); a ratio by itself has no units (e.g., refractive index n).

Scalar quantity

A quantity that has magnitude only, with no direction (e.g., mass, time, temperature, speed, distance).

Vector quantity

A quantity that has both magnitude and direction (e.g., weight, force, velocity, displacement, acceleration).

Mass

The amount of substance in a body; a scalar quantity measured in kilograms (kg).

Weight

The force of gravity on a body; a vector quantity measured in newtons (N); W = mg.

Gravitational field strength (g)

Force per unit mass at a point in a gravitational field; g = W/m; SI unit N/kg (≈9.8–10 m/s² near Earth).

Density

Mass per unit volume (ρ = m/V); determines whether an object sinks or floats in a medium.

Pressure

Force acting per unit area; SI unit Pascal (Pa = N/m²); a scalar quantity. P = F/A.

Period (T)

Time taken for one complete oscillation in a periodic motion.

Frequency (f)

Number of complete oscillations per second; measured in hertz (Hz).

Speed (v)

Rate of motion; for waves, v = frequency × wavelength.

Displacement

Straight-line distance from the starting point to the end point in a specific direction; a vector quantity.

Distance

Total length of path travelled, regardless of direction; a scalar quantity.

Acceleration

Rate of change of velocity; a = Δv/Δt; units m/s².

Uniform (constant) acceleration

Acceleration that does not change with time; shown as a straight-line gradient in a velocity-time graph.

Displacement–time graph

Graph showing how displacement changes with time; its gradient gives velocity.

Velocity–time graph

Graph showing how velocity changes with time; its gradient gives acceleration; area under the curve gives distance.

Free fall acceleration

Acceleration near Earth’s surface due to gravity, approximately 10 m/s² (often taken as 9.8 m/s²).

Mass vs. weight

Mass is the amount of substance (scalar, kg); weight is the gravitational force on a mass (vector, N). W = mg.

Free-body diagram

A diagram that shows all forces acting on an object, such as weight, normal force, friction, tension, and air resistance.

Newton’s Laws (conceptual use)

1st Law: equilibrium (balanced forces); 2nd Law: F = ma; 3rd Law: action-reaction pairs.

Centre of gravity (cg)

The point where the entire weight of a body appears to act; affects stability.

Torque (moment)

Turning effect of a force; moment = force × perpendicular distance from pivot.

Stability

Depends on base area and vertical position of the centre of gravity; larger base and lower cg increase stability.

Friction

Opposes motion; converts some energy to heat; affects motion and terminal velocity.

Terminal velocity

Constant maximum speed when drag balances weight; net force is zero.

Balanced vs. unbalanced forces

Balanced: resultant force is zero, no acceleration; Unbalanced: resultant force causes acceleration.

Work

Energy transferred when a force acts over a distance in the force’s direction (WD = F × d); unit joule (J).

Power

Rate of doing work or energy transfer; P = WD/t = E/t; unit watt (W).

Efficiency

Useful output energy ÷ total input energy × 100%.

Kinetic energy

Energy of motion: Ek = ½ mv².

Gravitational potential energy

Energy due to height: GPE = mgh.

Internal energy

Total kinetic and potential energy of particles in a system; changes with temperature.

Energy conservation

Energy cannot be created or destroyed; it can transfer or convert forms; total energy remains constant.

Heat (thermal) capacity

Amount of energy needed to raise the temperature of a substance by 1 K (or 1°C); unit J/K (or J/kg·K for specific).

Specific heat capacity

Energy needed to raise the temperature of 1 kg of a substance by 1 K (J/kg·K).

Latent heat

Heat required for a change of state without a temperature change.

Latent heat of fusion

Latent heat required to melt a solid (solid to liquid) per unit mass.

Latent heat of vaporisation

Latent heat required to boil a liquid (liquid to gas) per unit mass.

Conduction

Heat transfer by molecular interactions and free electrons within a substance (especially metals).

Convection

Heat transfer by fluid motion; warmer, less dense fluid rises.

Radiation

Transfer of energy by electromagnetic waves; does not require a medium.

Brownian motion

Random motion of particles suspended in a fluid due to continuous bombardment by molecules.

States of matter

Solid, liquid, gas; different arrangements and motions of particles and strength of forces.

Wave

A transfer of energy through a medium (or vacuum for EM waves) via oscillations, without bulk movement of matter.

Transverse vs. longitudinal waves

Transverse: oscillations perpendicular to the direction of travel (e.g., EM waves, rope); Longitudinal: oscillations parallel to travel (e.g., sound).

Speed of sound in air/liquid/solid

Approx. 330 m/s in air, ~1500 m/s in liquids, ~3000 m/s in solids (varies by medium).

Amplitude

Maximum displacement of a vibrating body from its rest position.

Reflection

Bounce of a wave off a surface; angle of incidence equals angle of reflection.

Angle of incidence (i)

Angle between incident ray and the normal to the surface.

Angle of reflection (r)

Angle between reflected ray and the normal; i = r for reflection.

Refraction

Bending of a wave as it passes between media with different speeds; governed by n = sin i / sin r.

Refractive index (n)

n = c/v; ratio of speed of light in vacuum to speed in the medium.

Critical angle

Incident angle in a denser medium for which refraction angle is 90°.

Total internal reflection

Occurs when incident angle > critical angle; light remains in denser medium; used in optical fibers.

Optical fibre

Thin flexible fiber using total internal reflection to transmit light signals.

Thin lens (converging/diverging)

Optical lens that focuses or diverges light rays; focal length and principal axis determine image formation.

Focal length (f)

Distance from optical centre to the principal focus for a lens.

Real image

Image formed when rays actually converge; can be projected on a screen; inverted usually.

Virtual image

Image formed where rays appear to diverge from; cannot be projected on a screen; upright.

Ray diagram

A schematic drawing showing the paths of light rays to locate images formed by lenses.

Electric charge

Positive and negative charges; measured in coulombs (C).

Electric field

Region around a charge where a force would act on other charges.

Electric field lines

Direction of force on a positive test charge; lines radiate away from positive and toward negative charges.

Electromagnetic spectrum

All electromagnetic waves arranged by wavelength/frequency (gamma, X-ray, UV, visible, infrared, microwaves, radio).

Speed of EM waves in vacuum

All electromagnetic waves travel at approximately 3.0 × 10^8 m/s in vacuum.

Hazards of EM radiation

Overexposure can cause heating and ionisation of living tissue; ionising radiation can damage cells.

Echo

Sound reflection used to measure distance; time taken for round trip yields speed of sound.

Ultrasound

Sound waves with frequencies above 20 kHz used in medical imaging and navigation.