Definitions of Key Words

Definitions of Key Words

1. Chapter 1

   • Work - the energy transferred by a force
   • Elastic - a material able to regain its shape after it has been squished or stretched
   • Useful Energy - Energy transferred to where it is wanted in the way it is wanted
   • Wasted Energy - Energy that is not useful transferred
   • Dissipation of Energy - The energy that is not usefully transferred and stored in less useful ways
   • Power - The energy transformed in transferred per seconds. Measured in Watts

2. Chapter 2

   • Thermal Conductivity - Property of a material that determines the energy transfer through it by conduction
   • Infrared Radiation - Electromagnetic waves between microwaves and visible light on the electromagnetic scale
   • Black Body Radiation - The radiation emitted from a perfect black body
   • Perfect Black Body - a body that absorbs all the radiation that hits it
   • Specific Heat Capacity - Energy needed to raise the temperature of 1kg of a substance by 1'C

3. Chapter 3

   • Biofuel - Any fuel taking from living or recently living materials (e.g. animal waste)
   • Renewable Energy - Energy from natural sources that is always being replenished so never runs out
   • Carbon-neutral - A biofuel from a living organism that takes in as much carbon dioxide from the atmosphere as is released when the fuel is burned
   • Nuclear Fuel - Substance used in nuclear reactors that releases energy due to nuclear fission
   • Nucleus - tiny positively charged object composed of protons and neutrons at the centre of every atom
   • Reactor Core - The thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor
   • Geothermal Energy - Energy that comes from energy released by radioactive substances deep within the Earth

4. Chapter 4

   • Protons - positively charged particles
   • Neutrons - Uncharged particles
   • Ion - A charged atom
   • Electric Field - A field around a charged object which causes a non-contact force on any other charged objects in its field
   • Electrons - Tiny negatively charged particles
   • Series - Components connected in a circuit such that the same current passes through them all
   • Potential Difference - The difference of electrical potential between two points. It is measured in Volts
   • Parallel - Components connected in a circuit such that the potential difference is the same for all
   • Resistance - The potential difference divided by the current passing through the component. It is measured in Ohms
   • Diode - A non-ohmic conductor that has a much higher resistance in its reverse direction than its forward direction
   • Light Emitting Diode - A diode that emits light when it conducts
   • Thermistor - A resistor whose resistance depends on its temperature
   • Light Depending Resistor - A resistor whose resistance depends on the intensity of the light incident on it

5. Chapter 5

   • Direct Current - Electric current in a circuit that is in one direction only
   • Alternating Current - Electric current in a circuit that repeatedly reverses its direction
   • Live Wire - The mains wire that has a voltage
   • Neutral Wire - The wire of a mains circuit that is earthed at the local substation so its potential is close to zero
   • Oscilloscope - A device used to display the shape of an electrical wave
   • Earth Wire - The wire in a mains cable used to connect the metal case of an appliance to earth
   • Fuse - contains a thin wire that melts and cuts the current off if too much current passes through it

6. Chapter 6

   • Density - Mass per unit volume of a substance
   • Physical Changes - A change in which no new substances are produced
   • Melting point - Temperature at which a pure substance melt or freezes
   • Boiling Point - Temperature at which a pure substance boils or condenses
   • Freezing Point - The temperature at which a pure substance freezes
   • Latent Heat - The energy transferred to or from a substance when it changes its state
   • Internal Energy - The energy of the particles of a substance due to their individual motion and positions
   • Specific Latent Heat of Fusion - Energy needed to melt 1kg of a substance with no change of temperature
   • Specific Latent Heat of Vaporisation - Energy needed to boil away 1kg of a substance with no change of temperature

7. Chapter 7

   • Alpha Radiation - Alpha particles, each composed of two protons and two neutrons, emitted by unstable nuclei
   • Beta Radiation - Beta particles that are high-energy electrons created in, and emitted, from unstable nuclei
   • Gamma Radiation - Electromagnetic radiation emitted from unstable nuclei in radioactive substances
   • Atomic Number - the number of protons in an atom
   • Mass Number - The number of protons and neutrons in an atom
   • Isotopes - Atoms with the same number of protons but different numbers of neutrons
   • Ionisation - Any process in which atoms become charged
   • Irradiated - An object that has been exposed to ionising radiation
   • Activity - The number of unstable atoms that decay per second in a radioactive source
   • Count Rate - The number of counts per second detected by a Geiger counter
   • Half-life - Average time taken for the number of nuclei of the isotope (or mass of the isotope) in a sample to halve
   • Nuclear Fission - The process in which certain nuclei (uranium-235 and Plutonium-239) split into two fragments, releasing energy and two or three neutrons as a result
   • Chain Reaction - Reactions in which one reaction causes further reactions, which in turn cause further reactions
   • Moderator - Substance in a nuclear reactor that slows down fission neutrons
   • Nuclear Fusion - The process where small nuclei are forced together to fuse and form a larger nucleus

8. Chapter 8

   • Displacement - Distance in a given direction
   • Vector - A physical quantity that has a magnitude and a direction (e.g. displacement)
   • Scalar - A physical quantity that has magnitude only (e.g. mass)
   • Magnitude - The size or amount of a physical quantity
   • Forces - Can change the motion of an object. Measure in N, newtons
   • Newton's Third Law - When two objects interact with each other, they exert equal and opposite forces on each other
   • Friction - The force opposing the relative motion of two solid surfaces in contact
   • Resultant Force - A single force that has the same effect as all the forces acting on the object
   • Newton's First Law of Motion - If the resultant force on an object is zero, the object stays at rest if it is stationary, or it keeps moving with the same speed in the same direction
   • Moment - The turning effect of a force
   • Load - The weight of an object raised by a device used to lift the object, or the force applied by a device when it is used to shift an object
   • Principle of Moments - For an object in equilibrium, the sum of all the clockwise moments about any point = the sum of all the anti-clockwise moments about that point
   • Parallelogram of forces - A geometrical method used to find the resultant of two forces that do not act along the same line

9. Chapter 9

   • Velocity - Speed in a given direction. Measured in m/s
   • Acceleration - Change of velocity per second. Measured in m/s²
   • Deceleration - Change of velocity per second when an object slows down

10. Chapter 10

    • Newton's Second Law of Motion - The acceleration of an object is proportional to the resultant force on the object, and inversely proportional to the mass of the object
    • Inertia - The tendency of an object to stay at rest or to continue in uniform motion
    • Weight - The force of gravity on an object.
    • Mass - The quantity of matter in an object, a measure of the difficulty of changing the motion of an object. Measured in kg
    • Gravitational Field Strength - The force of gravity of an object of mass 1kg and also the acceleration of free fall. Measured in N/kg
    • Terminal Velocity - The velocity reached by an object when the drag force on it is equal and opposite to the force making it move
    • Stopping Distance - The distance travelled by the vehicle in the time it takes for the driver to think and brake
    • Thinking Distance - The distance travelled by the vehicle in the time it takes the driver to react
    • Braking Distance - The distance travelled by a vehicle during the time it takes for its brakes to act
    • Conservation of Momentum - In a closed system the total momentum before an event is equal to the total momentum after the event.
    • Extension - The increase in length of a spring from its original length
    • Limit of Proportionality - The limit for Hooke's law applied to the extension of a stretched spring

11. Chapter 11

    • Pressure - Force per unit area. Measure in Pa (Pascals) or N/m²

12. Chapter 12

    • Mechanical Waves - Vibration that travels through a substance
    • Electromagnetic Waves - Electric and magnetic disturbances that transfer energy from one place to another
    • Transverse Waves - A wave whose oscillations are perpendicular to the direction of energy transfer
    • Longitudinal Waves - Waves whose oscillations are parallel to the direction of energy transfer
    • Compression - Squeezing together
    • Refraction - The change of direction of a light ray when it passes across a boundary between two transparent substances
    • Wavelength - The distance from one wave crest to the next
    • Amplitude - The maximum distance moved by an oscillating object from its equilibrium position
    • Frequency - The number of wave crests passing a fixed point every second
    • Speed - The distance travelled by each wave every second through a medium
    • Reflection - The change of direction of a light ray or wave when it passes across a boundary when the ray or wave stay in the incident medium
    • Transmission - a wave passing through a substance
    • Echo - Reflection of a sound that can be heard
    • Ultrasound Waves - Sound waves at frequency greater than 20000Hz
    • Seismic Waves - Shock waves that travel through the Earth and across its surface as a result of an earthquake

13. Chapter 13

    • Radio Waves - Electromagnetic waves of wavelength greater than 0.10m
    • Microwaves - Electromagnetic waves between infrared and radio waves in the electromagnetic spectrum
    • Infrared Radiation - Electromagnetic waves between visible light and microwaves on the electromagnetic spectrum
    • Ultraviolet Radiation - Electromagnetic waves between visible light and x-rays on the electromagnetic spectrum
    • X-Rays - Electromagnetic waves smaller in length than ultraviolet waves
    • White Light - Light that includes all the colours of the spectrum
    • Carrier Waves - Waves used to carry an type of signal
    • Contrast Medium - An x-ray absorbing substance used to fill a body organ so it can be seen on a radiograph
    • Charge Couple Device - An electronic device that creates an electronic signal from an optical image formed on the CCD's array of pixels
    • Radiation Dose - Amount of ionising radiation a person receives

14. Chapter 14

    • Normal - Straight line through a surface or boundary perpendicular to the surface or boundary
    • Angle of Incidence - Angle between the incident ray and the normal
    • Angle of Reflection - Angle between reflected ray and the normal
    • Virtual Image - An image seen in a lens or a mirror, from which light rays appear to come after being refracted by a lens or reflected by a mirror
    • Specular Reflection - Reflection from a smooth surface where each ray is reflected in the same direction
    • Diffuse Reflection - Reflection from a rough surface so the rays are scattered in different directions
    • Convex Lens - A lens that makes the light rays parallel to the principal axis converge at a point
    • Principal Focus - The point where light rays parallel to the principal axis of a lens are focused
    • Magnifying Glass - A converging lens used to magnify small objects which must be placed between the lens and its focal point
    • Concave Lens - A lens that makes light rays parallel to the axis diverge

15. Chapter 15

    • Magnetic Field - The space around a magnet or a current-carrying wire
    • Electromagnet - An insulated wire wrapped round an iron bar that becomes magnetic when there is a current in the wire
    • Motor Effect - When a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field
    • Fleming's left-hand Rule - Gives the direction of a force on a current-carrying wire in a magnetic field according to the directions of the current and the field
    • Solenoid - A long coil of wire that produces a magnetic field in and around the coil when there is a current through it
    • Electromagnetic Induction - The process of inducing a potential difference in a wire by moving the wire so it cuts across the lines of flux
    • Generator Effect - The production of a potential difference using a magnetic field
    • Alternator - An alternating current generator
    • Dynamo - A direct current generator
    • Transformer - Electrical device used to change an alternating voltage
    • Step-up Transformer - Transformer used to increase the size of the alternating voltage
    • Step-down Transformer - Transformer used to decrease the size of the alternating voltage

16. Chapter 16

    • Protostar - The concentration of dust clouds and gas in space that forms a star
    • Main Sequence - The main sequence is the life stage of a star during which it radiates energy because of fusion of hydrogen nuclei in its core
    • Red Giant - A star that has expanded and cooled, resulting in it becoming red and much larger and cooler than it was before it expanded
    • White Dwarf - A star that has collapsed from the red giant stage to become much hotter and denser
    • Black Dwarf - A star that has faded out and gone cold
    • Red Supergiant - A star much more massive than the Sun will swell out after the main sequence stage to become a red supergiant before it collapses
    • Supernova - The explosion of a massive star after fusion in its core ceases and the matter surrounding its core collapses on to the core and rebounds
    • Neutron Star - The highly compressed core of a massive star that remains after a supernova explosion
    • Black Hole - An object in space that has so much mass that nothing, not even light, can escape from its gravitational field
    • Centripetal Force - The resultant force towards the centre of a circle acting on an object moving in a circular path
    • Redshift - Increase in the wavelength of electromagnetic waves emitted by a star or galaxy due to its motion away from us. The faster the speed of the star or galaxy, the greater its redshift
    • Big Bang Theory - The theory that the universe was created in a massive explosion and that the universe has been expanding ever since
    • Cosmic Microwave Background Radiation - Electromagnetic radiation that has been travelling through space ever since it was created shortly after the big bang
    • Dark Matter - Matter in a galaxy that cannot be seen. Its presence is deduced because galaxies would spin much faster if their stars were their only matter