Leaving Cert Physics definitions

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 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

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 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

n-type semiconductor

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