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Physics
Leaving Cert Physics definitions
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Gravity
Terms in this set (99)
Displacement
Displacement is distance in a given direction
Speed
Speed is the rate of change of distance with respect to time
Velocity
Velocity is the rate of change of Displacement with respect to time
Acceleration
Acceleration is the rate of change of velocity
Scalar quantity
A scalar quantity is one which only has magnitude
Vector Quantity
A vector quantity is one which has both magnitude and direction
Force
A force is anything that causes the velocity of an object to change
The newton
The newton is the force which gives a mass of one kg an acceleration of 1m/s
Friction
Friction is a force which opposes the relative motion between two objects
The weight
The weight of an object is the force of the Earth's gravity on it
Momentum
Momentum is the product of mass and velocity
Newton's 1st law of motion
body remains at rest/moves with constant velocity unless external force acts on it
Newton's 2nd law of motion
force proportional to // rate of change of momentum
Newton's 3rd law of motion
If object A exerts a force on object B, then B will exert an equal but opposite force on A
The principle of Conservation of Momentum
momentum before equals momentum after // in a closed system / provided no external forces act
Density
The density of a substance is a measure of its mass per unit volume
Pressure
Pressure is defined as force per unit area
Archimedes' Principle
States that when an object is immersed in a fluid, the upthrust it experiences is equal to the weight of the displaced fluid
The law of flotation
States that the weight of a floating object is equal to the weight of the fluid it displaces
Boyle's law
p and V inversely proportional //
for a fixed mass of gas at constant temperature
Newton's law of gravitation
force proportional to product of masses // inversely proportional to square of distance
Conditions for equilibrium of an object under Co-planar forces
The vector sum of the forces in any direction is zero. The sum of the moments about any point is zero
The moment of a Force
Moment is force × perpendicular distance from fulcrum
Work
Work is defined as the product of displacement by force
Energy
Energy is the ability to do work
The principle of conservation of energy
Energy is neither created nor destroyed, only converted from one form to another
Power
Power is the rate at which work is done or the rate at which energy is converted from one form to another
Angular velocity
Angular velocity is the rate of change of angle with respect to time
Centripetal force
Centripetal force is the force acting in towards the centre required to keep an object moving in a circle
Hooke's Law
extension proportional to // (applied )force
Temperature
The temperature of an object is a measure of the hotness of coldness of that object
A thermometric property
Any (physical) property that changes (measurably) //
with temperature
The specific latent heat
Heat needed to change the state // of 1 kg of a substance (with no change in temperature)
The Specific heat capacity
The specific heat capacity of a substance is the heat energy needed to change 1 kg of the substance by 1 Kelvin
The specific latent of fusion
The specific latent of fusion is the amount of heat energy needed to change 1 kg of the substance from a solid to a liquid without a change in temperature
The specific latent of vaporisation
The specific latent of vaporisation is the amount of heat energy needed to change 1 kg of the substance from a liquid to a gas without a change in temperature
The U-Value
The U-value of a structure is the amount of heat energy conducted per second through 1 m squared of that structure when a temperature difference of 1 K is maintained between its ends
Conduction
Conduction is the movement of heat energy through a substance by the passing on of molecular vibration from molecule to molecule, without any overall movement of the substance
Convection
Convection is the transfer of heat through a fluid by means of circulating currents of fluid cause by the heat
Radiation
Radiation is the transfer of heat energy from one place to another in the form of electromagnetic waves
Reflection
Light rebounding (off surfaces)
The 1st law of reflection of light
Incident ray, refracted ray and normal at the point of incidence all in same plane
The 2nd law of reflection of light
The angle of incidence is equal to the angle of reflection
A real image
A real image is an image formed by the actual intersection of light rays
A virtual image
A virtual image is formed by the apparent intersection of light rays
Refraction
Refraction is the bending of light as it passes from one medium to another
The 1st law of refraction of light
The incident ray, the normal at the point of incidence and the refracted ray all lie in the same plane
The 2nd law of refraction of light (Snell's law)
The sine of the angle of incidence divided by the sine of the angle of refraction is a constant
The refractive index of a medium
The refractive index of a medium is the ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium
Short-sighted (definition and correction)
A short-sighted person can see nearby objects clearly but cannot bring distant objects into focus. Corrected with a concave lens
Long-sighted (definition and correction)
A long-sighted person can see distant objects clearly but cannot bring nearby objects into focus. Corrected with a convex lens
A transverse wave
A transverse wave is a wave where the direction of the vibration is perpendicular to the direction in which the wave travels
A longitudinal wave
A longitudinal wave is a wave where the direction of vibration is parallel to the direction in which the wave travels
Diffraction
the spreading of a wave // into the space beyond a barrier/obstacle/gap
Interference
the addition/(meeting) of two or more waves (to form a new wave)
Constructive interference
Constructive interference occurs when two waves combine to produce a wave of greater amplitude
Destructive interference
Destructive interference occurs when two waves combine to produce a wave of lower amplitude
Coherent sources
same frequency/wavelength // and are in phase
A polarised wave
A polarised wave is a wave which vibrates in one plane only
Stationary waves
Stationary waves are formed when two periodic travelling waves of the same frequency and amplitude travelling in opposite directions meet
The Doppler effect
the (apparent) change in the frequency (of a wave) //
due to the relative motion between the source (of the wave) and the observer
The natural frequency
The natural frequency of an object is the frequency at which the object will vibrate if free to do so
Resonance
transfer of energy between two systems // of similar natural frequencies
Dispersion
Separation of light // into its different colours /frequencies / wavelengths
The coulomb
Is the charge that passes when 1 A flows for 1 second
Coulomb's Law
force proportional to product of charges // and inversely proportional to square of distance
Electric field
an electric field is a region (of space)// where electrostatic forces are experienced / forces experienced by charged particles
Electric field strength
Force per // unit charge
Potential difference (is one volt if)
work per // unit charge
The volt
potential difference (between two points) if 1 J (of work) is needed // to move 1 C (from one point to the other)
The potential at a point
The potential at a point refers to the work done in bringing unit charge from that point to earth
Capacitance
capacitance is the ratio of charge (on a capacitor) //
to the potential difference (across it)
Current
Current is a flow of charge
EMF
Emf is voltage when applied to a circuit
The resistance of a conductor
The resistance of a conductor is the ratio of the potential difference across it to the current flowing through it
Ohm's Law
States that the current flowing through a conductor is directly proportional to the square of the current provided its resistance is constant
A semiconductor
A semiconductor is a material whose resistivity is between that of a good conductor and a good insulator
Intrinsic conduction
Intrinsic conduction is the movement of charges through a pure semiconductor
Extrinsic conduction
Extrinsic conduction is the movement of charges through a doped semiconductor
Doping
Doping is the addiction of a small amount of atoms of another element to a pure semiconductor to increase its conductivity
An n-type semiconductor
An n-type semiconductor is a semiconductor in which electrons are the majority charge carriers
A p-type semiconductor
A p-type semiconductor is a semiconductor in which holes are the majority charge carriers
Ampere
Ampere is that current which, if flowing in two, infinitely long, parallel wires, of negligible cross-sectional area, one metre apart, in a vacuum, experiences a force of 2 X 10 to the -7 N per metre
Electromagnetic induction:
(when) a conductor/wire cuts magnetic flux //
an emf /voltage is induced
Faraday's Law
(size of an) induced emf is proportional to // the rate of change of flux (through a circuit)
Lenz's Law
States that the directions of the induced emf is always such as to oppose the change producing it
Magnetic Flux
Magnetic flux is the product of flux density by area
Ionisation
Ionisation occurs when an atom loses electrons
Thermionic emission
the emission of electrons // (from the) surface of a hot metal
MCB
Miniature Circuit Breaker
RCD
Residual current device
Chain reaction
a (self-sustaining) reaction where the release of one or more neutrons causes further fission
Nuclear fission
fission is the splitting of a large nucleus // into two (smaller) nuclei with the release of energy/neutrons
Nuclear fussion
two small nuclei join // to form a larger nucleus
The becquerel
one disintegration per second
Positron
An electron with + charge
Anti-matter
material/matter/particle that has same mass as another particle // (but equal in magnitude and) opposite charge
Pair production
particle and (its) antiparticle created // from energy / gamma rays
Photon
packet/bundle/quantum // of (light) energy/electromagnetic radiation
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