List of Definitions
* are those appears more frequently in GCE O-Level Examination
Absolute zero (0 K): The lowest possible temperature that exists in the universe.
*Acceleration: The change in velocity with time.
Acceleration due to gravity: The rate at which all objects fall towards Earth if there were no air resistance, approximately 10 ms^(-2) near Earth's surface
a.c generator: A a.c generator makes use of electromagnetic induction to convert mechanical energy into useful electrical energy
Alternating current: An electric current that periodically reverses its direction in the circuit
*Amplitude: Maximum distance from the rest or central position, in either direction.
Angle of incidence: The angle between the incident ray and the normal.
Angle of reflection: The angle between reflected ray and the normal.
Angle of refraction: The angle between refracted ray and the normal.
Atmospheric pressure: The pressure due to air molecules colliding with the surfaces of bodies.
At sea level, atmospheric pressure is 1 atm or 1.013 * 10^5 Pa
Average speed: Total distance travelled divided by total time taken.
Barometer: An instrument to measure atmospheric pressure
Boiling: A change of state from a liquid to a gas without a change in temperature. For a pure substance, it occurs at a constant temperature called boiling point.
*Brownian motion: The constant random motion of tiny particles suspended in a fluid (i.e. smoke particles in air or pollen grains in water).
Carbon Brush: To make good electrical contact with the external and internal circuits.
Cathode-Ray Oscilloscope: A common electronic device used to study waveforms, measure voltage and short intervals of time
Celsius scale: A temperature scale where the lower fixed point is the ice point (0°C) and the upper fixed point is the steam point (100°C)
*Centre of gravity (CG): The point through which its whole weight appears to act for any orientation of the object.
Centre of mass: The point which its entire mass seems to act.
Circuit breakers: Safety devices that can switch off the electrical supply in a circuit when the current flowing is greater than its current rating
Compression: A region in which air particles are pushed towards each other and the air is at a pressure higher than surrounding air pressure
Condensation: A change of state from a gas to a liquid without a change in temperature. A pure substance condenses at a temperature equal to its boiling point.
Conduction: The transfer of thermal energy without any flow of the material medium.
Conductor: Materials that allow electrons to move freely within the material
Convection: The transfer of thermal energy by means of currents in fluids (liquids or gases).
Convection current: The movement of fluid caused by the change in density in various parts of the fluid.
Converging lens or Convex lens: Lens that is thicker in the middle than at the edges will make parallel light rays converge to a point
Crest: Highest point of a wave
*Critical angle: The angle of incidence in the optically denser medium for which the angle of refraction in the less dense medium is 900.
*Current: The rate of flow of charge
d.c Motor: A d.c. motor makes use of the turning effect of a current-carrying coil in a magnetic field to convert electrical energy into mechanical energy
Density: Mass per unit volume
Discharging: A process to neutralize a charged object by removing the excess charges
Displacement: The shortest distance travelled from starting position to ending position.
Distance: The length of path travelled. It does not depend on direction.
Diverging lens or Concave lens: Lens that is thinner in the middle than at the edges will make parallel light rays diverge
Echo: It is formed when a sound is reflected by large, hard and flat surfaces like buildings, walls and cliffs.
Electric circuit: A complete path which charges can flow from one terminal of electric source to another terminal
Electric field: A region where an electric charge experiences an electric force
Electromagnet: Consists of a coil made from insulated copper wire wound on a core of soft magnetic material like iron. When a current flows through the coil, the core becomes a magnet.
Electromagnetic Wave (EM Wave): EM waves are transverse waves, consist of electric and magnetic waves at right angles to each other and to the direction of wave propagation.
*Electromotive Force: Work done by the source to drive a unit charge round a complete circuit
Emergent ray: Refracted ray backs to the original medium. It is parallel to the incident ray.
*Energy: The capacity to do work.
Evaporation: A process which a substance changes its state from liquid to gas without boiling.
*Faraday's law of induction: It states that the magnitude of the induced e.m.f. in a circuit is directly proportional to the rate of change of magnetic field lines cutting it
Fixed point: The standard degree of hotness or coldness such as a melting or boiling point of a substance.
*Fleming’s Left Hand Rule: It states that the direction of force (indicated by Thumb) is perpendicular to both the direction of magnetic field from North pole to South pole (indicated by Index Finger) and the direction of current (indicated by Middle Finger).
*Fleming’s Right Hand Rule: It states that the direction of induced current (indicated by Middle Finger) is perpendicular to both the direction of magnetic field from North pole to South pole (indicated by Index Finger) and the direction of movement or motion (indicated by Thumb).
*Focal length: The distance between the optical centre C and the focus point F
Focal plane: The plane which passes through the focal point and is perpendicular to the principal axis
Focal point (for converging lens): The point where all rays parallel to the principal axis converge after refraction by the lens.
Focal point (for diverging lens): The point where all rays parallel to the principal axis are brought to a focus in front of the lens
Force: It is either a push or pull that one object exerts on the other object
Free fall: An object is in 'free fall' if the only force acting on it is the weight or the force due to gravity
Freezing or solidification: A change of state from a liquid to a solid without a change in temperature. A pure substance freezes at a temperature equal to its melting point.
*Frequency: Number of complete waves produced per second
Friction: A force which always opposes the motion between two surfaces in contact
Fuse: Safety device to prevent excessive current flow and hence protect wires and electrical appliance from overheating and damaged
Gravitational field: A region where an object experiences a force due to gravitational attraction.
Gravitational field strength: The gravitational force acting per unit mass on an object.
On Earth, g = 10 N/kg
Gravitational potential energy: The energy which a body possesses because of its position relative to the ground.
Heat: the amount of thermal energy that is being transferred from a hotter to a colder object (Quantity of hotness)
*Heat capacity: Amount of heat required to increase the temperature of the object by 1 K or 1⁰C
Heat Transfer / Thermal energy transfer: Thermal energy is transferred only when there is a difference in the temperature and it always flows from a region of higher temperature to a region of lower temperature.
*Ice Point: The temperature of pure melting ice at one atmospheric pressure and has a value of 0⁰C.
Incident ray (for reflection): Light ray striking the reflecting surface
Incident ray (for refraction): Light ray striking the boundary
Induction (for electrostatic): A method used to charge a conductor without any contact with the charging body
Inertia: The reluctance of the object to change its state of rest or motion
Infrasound: Sound waves with frequencies below the lower limit of the human range of audibility (below 20 Hz).
Input transducers: Transducers that change non-electrical energy to electrical energy
Insulators: Materials where electrons remain on the surface of it and do not move about freely within the material
Internal energy: The sum of the kinetic energy (due to motion) and potential energy (due to intermolecular forces) of the molecules of a body.
Kinetic energy: The energy a body possessed due to its motion
Kinetic Model of Matter: It describes that all matter being made up of tiny particles are in continuous random motion
Latent heat: The energy absorbed or released when there is a change in state.
*Latent heat of fusion: The amount of heat needed to change the substance from solid to liquid, or vice versa, without a change in temperature.
*Latent heat of vaporisation: The amount of heat needed to change the substance from liquid to gas, or vice versa, without a change in temperature.
Law of electrostatic: Like charges repel, unlike charges attract
Law of Magnetism: Like poles repel, unlike poles attract
*Laws of reflection:
*Laws of refraction:
First Law: The incident ray, the normal and the refracted ray all lie in the same plane.
Second Law: For two particular mediums, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
i.e sin i⁄sin r = constant
*Lenz's law: It states that the direction of the induced e.m.f. (and hence induced current in a closed circuit) is always such that its magnetic effect opposes the change producing it
Light Dependent Resistor (LDR): A device that has a resistance changes with light intensity (amount of light) shining on it.
Linear magnification: The ratio of image height to the object height
Longitudinal Waves: Waves which travel in a direction parallel to the direction of the vibration.
Loudness: Loudness is related to the amplitude of a sound wave
Luminous objects: Objects that give off light
Magnetic domain: A group of atomic magnets pointing in the same direction
Magnetic field: The region around a magnet where a magnetic material experiences a magnetic force
Magnetic induction: A process where a magnetic material becomes an induced magnet when it is brought near to or in contact with a magnet
Magnetic Materials: Materials that can be magnetized or attracted by magnets
Magnetic shielding: It is to prevent surrounding magnetic field lines from reaching the magnetic-sensitive equipments whose operation may be affected by the fields
Manometer: An instrument to measure the difference in the pressure of gases or liquids
Mass: The amount of substance in a body
Melting: A change of state from a solid to a liquid without a change in temperature. For a pure substance, it occurs at a constant temperature called melting point.
*Moment: The product of the force and the perpendicular distance from the pivot to the line of action of the force.
Motor Effect: When a current-carrying conductor is placed in a magnetic field, the conductor will experience a force. This effect on the conductor is called the Motor Effect
Neutral equilibrium: If it stays in its new position after being displaced, it is said to be in neutral equilibrium.
Neutral point (for charges): The electric fields from both charges cancel out each other
Neutral point (for magnets): The magnetic fields from both magnets cancel out each other
Newton’s First Law: It states that every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it.
This is also known as Law of inertia.
Newton’s Second Law: It states that when a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force. The product of the mass and the acceleration of the object gives the resultant force.
Newton’s Third Law: It states that for every action, there is an equal and opposite reaction, and they act on mutually opposite bodies.
Non-luminous objects: Objects do not give off light. A light source is required in order for us to see non-luminous objects.
Non-Magnetic Materials: Materials that cannot be magnetized or attracted by magnets
Non-ohmic Conductors: Conductors do not obey ohm’s law
Normal (for reflection): An imaginary line perpendicular to the reflecting surface at the point of incidence.
Normal (for refraction): An imaginary line perpendicular to the boundary at the point of incidence.
North Pole: The end of the magnet that points to the northern end of the Earth
*Ohm’s Law: It states that the current passing through a metallic conductor is directly proportional to the potential difference across it, provided that physical conditions (like temperature) remain constant
Ohmic Conductors: Conductors that obey ohm’s law
Optical centre: The midway point between the lens’ surfaces on its principal axis. Rays passing through the optical centre are not deviated
Optical Density: A measure of how much the speed of light is slowed down when it passes through a medium.
*Period: Time taken for one complete oscillation
Phase: Any two points are in phase when they move in the same direction with same speed and have same displacement from the rest or central position.
Pitch: Pitch is related to the frequency of a sound wave
Point of incidence (for reflection): The point on the reflecting surface where the light ray strikes.
Point of incidence (for refraction): The point on the boundary where the light ray strikes.
*Potential Difference: Work done to drive a unit charge through a component or across two points
Potential divider: A simple circuit with resistors arranged in series to obtain a fraction of the main voltage provided by a voltage supply
Potentiometer: A variable resistor that is connected at three terminals shown as points A, B, C. Contact C is a sliding contact
*Power: The rate of work done or rate of energy conversion
*Pressure: Force acting per unit area
Principal axis: The line passing symmetrically through the optical centre of the lens
*Principle of Conservation of Energy: It states that energy can neither be created nor destroyed in any process. It can be converted from one form to another but the total amount remains constant.
*Principle of moment: It states that when a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot.
Radiation: The continual emission of infra-red (IR) waves from the surface of all bodies, transmitted without the medium.
Rarefaction: A region in which air particles are pulled from each other and the air is at a pressure lower than surrounding air pressure
Real image: An image that can be captured on a screen
Rectification: Convert a.c to d.c
Reflected ray: Light ray reflected from the reflecting surface
Reflection of light: The change in direction of light rays that strike the boundary between different mediums.
*Refraction: The bending of light rays when it passes from one optical medium to another
*Refractive Index: The ratio of the speed of light in vacuum to the speed of light in the medium.
Resistance: The ratio of the potential difference V across it to the current I passing through it.
Right hand grip rule: It is used to determine the polarity of a permanent magnet produced.
Thumb represents the North pole of a magnet;
Curling fingers represents the direction of current flow
Scalar quantities: Quantities with magnitude only, like length, mass
*Slip Ring: To transfer the alternating induced current in the coil to the external circuit
Sound: A form of energy propagated from one point to another as a wave.
South Pole: The end of the magnet that points to the southern end of the Earth.
*Specific heat capacity: Amount of heat required to increase the temperature of 1 kg (unit mass) of the substance by 1 K or 1⁰C
*Specific latent heat of fusion: The amount of heat needed to change 1kg of the substance from solid to liquid, or vice versa, without a change in temperature.
*Specific latent heat of vaporisation: The amount of heat needed to change 1kg of the substance from liquid to gas, or vice versa, without a change in temperature.
*Speed: The distance moved per unit time.
*Split Ring: To reverse the direction of the current in the coil every half a revolution (or whenever it changes contact from one brush to another). This ensures that the coil always rotates in the same direction.
Stable equilibrium: If the object returns to its original position without toppling after being displaced slightly, it is said to be in stable equilibrium.
*Stability: The ability of an object to return to its original position after it has been tilted slightly.
*Steam point: The temperature of steam from pure water boiling at one atmospheric pressure and has a value of 100⁰C.
Temperature: how hot or cold an object is (degree of hotness)
Thermal Equilibrium: When two objects are at same temperature, they are in thermal equilibrium. This means there is no net flow of thermal energy between them.
Thermistor: A device that has a resistance changes with temperature
Thermometric substances: Substances (solid, liquid or gas) that have physical properties that vary continuously and linearly with temperature
*Total internal reflection: The complete reflection of light rays within an optically denser medium.
Transducers: Devices that transform energy from one form to another
Transformer: A device that can change a high alternating voltage to a low alternating voltage, or vice verse
*Transverse Waves: Waves which travel in a direction perpendicular to the direction of the vibration.
Trough: Lowest point of a wave
Ultrasound: Sound waves with frequencies above the upper limit of the human range of audibility (above 20 kHz).
Unstable equilibrium: If it continues to move away from its original position after being displaced, it is said to be in unstable equilibrium
Vector quantities: Quantities with both magnitude and direction, like velocity, force.
*Velocity: Change in displacement per unit time
Virtual image: An image that cannot be captured on a screen
Wave: A phenomenon in which energy is transferred from one point to another without the transfer of any material medium through vibrations
*Wavefront: An imaginary line joining all the crests or troughs in a wave
*Wavelength: Shortest distance between two consecutive crests or troughs of a wave or any two points that are in phase
Wave Speed: Distance travelled by a wave per unit time
Weight: The amount of gravitational force acting on a body.
It is also known as gravitational force or gravity.
*Work done: Work is done only when the object moves in the direction of force and is given as the product of the force and the distance moved by the object in the direction of the force.