Physics Leaving Cert Definitions

Heat

Thermal energy measured in joules

Temperature

A measure of how hot or cold something is.

Thermometric property

A physical property that changes measurably and repeatably with temperature change

specific heat capacity

The amount of heat energy required to change 1kg of an object by 1℃

Latent heat

The heat energy required to change the state of a substance without changing its temperature

Specific Latent Heat

Amount of heat needed to change the state of 1 kg of a substance without a change in temperature.

Specific latent heat of vaporisation

The amount of heat energy needed to change 1 kg of a substance from a liquid to a gas without a change in temperature

Specific latent heat of fusion

The amount of heat energy needed to change 1kg of a substance from a solid to a liquid without a change in temperature

Conduction

The transfer of heat energy in a solid by passing on kinetic energy from molecule to molecule

Convection

the transfer of heat energy by the circulation of the heated parts of a liquid or gas.

Radiation

the transfer of heat energy as electromagnetic waves without the need for a medium

Solar constant, solar irradiance

The amount of solar energy striking 1m² of the earths atmosphere every second 1.35KW/M2

U-value

The amount of heat energy that can be transmitted across 1m² of an object's surfaces every second, so long as there is a temperature difference of 1°c on each side of the object

Zero error

the amount you need to add or subtract to make your starting point zero. Due to wear and tear of equipment, some instruments need to be 'zeroed' before use.

Scalar

a quantity that has magnitude but no direction

Vector

A quantity that has magnitude and direction

Displacement

the distance moved in a particular direction

Velocity

the rate of change of displacement with time

Constant velocity

an object that doesn't speed up, slow down or change direction.

Acceleration

the rate of change of velocity with time

Force

Anything that makes an object move or change velocity

Momentum (p)

The product of a bodies mass and velocity. p=mv

Newtons first law of motion

All bodies will remain at rest or at constant velocity unless an external force acts on them.

Newton's Second Law of Motion

The rate of change of a body's momentum is proportional to the net force applied and will act in the direction of the force

Newton's Third Law of Motion

Every action has an opposite but equal reaction

Principle of conservation of momentum

The total momentum of a system before an interaction is equal to the total momentum of the system after an interaction, so long as no external force acts on it. m₁u₁+m₂u₂=m₁v₁+m₂v₂

Newton's law of universal gravitation

Every mass in the universe attracts every other mass with a force, along the line of their centres, that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

Watts

Joules per second

Normal

a line perpendicular to a surface. The normal is always drawn perpendicular to a mirror at the incident point

Plane

A two dimensional surface

Laws of reflection

-incident ray, reflected ray and the normal all lie in the same plane

-angle of reflection (r) is equal to the angle of incidence (i)

Real image

an image created by the real intersection of light rays

virtual image

an image created by the apparent intersection of light rays

Parallax

the difference in the apparent position if an object viewed along two different lines of sight

object distance

The distance from the mirror or lens to the object

image distance

The distance from the mirror or lens to the image formed

focal length

the distance from a mirror or lens to its focal point

Power of a lens

The power of a lens is it's ability to converge or diverge light rays. It is measured in M^-1

P=1/f

Long sighted

When someone can see distant objects more clearly than close objects

Hyperopia

fixed with convex lens

Short sighted

When someone can see close objects more clearly than distant objects

Myopia

concave lens to fix

Refraction of light

the bending of light at a boundary as it passes from one transparent medium to another

Laws of refraction

Incident ray and refracted ray all lie in the same

the ratio of the sine of angle of incidence (i) to the sine of the angle of refraction (r) is a constant called the refractive index

refractive index of a medium

n=sini/sinr, when the ray travels from a vacuum into the medium

refractive index between two media

aNb is the value of sin i/sin r when the ray of light travels from medium a into medium b

critical angle

the angle of incidence when travelling from a denser medium to a rarer medium that results in an angle if refraction of 90°

total internal reflection

occurs when a light ray travelling from a denser medium to a rarer medium at an incident angle greater than the critical angle, is completely reflected

Mechanical waves

waves that require a medium to travel through and physically disrupt that medium

electromagnetic waves

waves that do not require a medium to travel through and cause electric and magnetic disruption

travelling waves

Carry energy through a medium without any overall movement of the medium

Longitudinal waves

waves that vibrate parallel to the direction that the wave is travelling

Transverse waves

waves that vibrate perpendicular to the direction that the waves is travelling

Reflection

the bouncing of a wave off an object

refraction

the bending of a wave as it enter a different medium and changes speed

diffraction

the spreading out of a wave as it moves through a gap or around an obstacle

Interference

when waves combine to form a resultant amplitude made up of each waves individual amplitude

constructive interference

when waves combine to form an amplitude greater than each waves individual amplitude

destructive interference

when waves combine to form an amplitude smaller than each waves individual amplitude

polarisation

when a wave's vibrations are confined to one particular plane

only occurs with transverse waves

stationary waves

Waves of the same frequency and amplitude that constructively and destructively interfere to produce a wave pattern in a confined space

The Doppler effect

the apparent change in frequency due to the relative motion of source and observer

characteristics of notes

frequency defines the pitch

amplitude defines how loud it is

the quality is the relative strength and overtones present

Overtones

integer multiples of the fundamental frequency. The first overtone is at 2f.

Harmonics

integer multiples of fundamental frequency. The first one is at f

Intensity of a sound

the rate of sound energy incident on 1M^2 at a right angle to the direction of the motion of the sound

I=P/A

Resonance

the transfer of energy between two bodies with the same natural frequency

fundamental frequency

when a vibrating string has an antinode in the centre and one node at each end

Diffraction grating

a large number of parallel slits/gaps constructed into a transparent material

Dispersion

the separating of white light into it's constituent colours

primary colours

the three colours that combine to make white light

red, green, blue

secondary colours

the colours formed from combining equal amounts of primary colours together

yellow, magenta, cyan

complementary colours

primary and secondary colours that combine to make white light

Density

an objects mass per unit volume

kgm^-3

pressure

an objects force per unit area

Pa or Nm^-2

Boyle's law

for a gas at a fixed mass and temperature its volume is inversely proportional to its pressure

Archimedes principle

whenever an object is totally or partially immersed in a fluid it experiences an up thrust that is equal to the weight of the fluid it displaces

Law of flotation

whenever an object is floating, the weight of the fluid displaced will equal the object's weight

Lever

A rigid bar that is free to rotate about a fixed fulcrum

fulcrum - (the point at which a lever turns or is supported)

Moment of a force

the magnitude of the force multiplied by the perpendicular distance from the axis to the force

Couple

a pair of parallel equal forces that turn in opposite directions

Work

is the energy given to a body by a force moving it through a displacement in the same direction as the applied force

Energy

the ability to do work

Law of Conservation of Energy

Energy cannot be created or destroyed, but can be converted from one form to another

Potential energy

energy due to position or conformation

kinetic energy

energy due to movement

Power

the rate at which work is done

Efficiency

power output divided by input

laws of equilibrium for a set of co-planar forces

The sum of the forces in any direction is 0

the sum of the moments about any axis is 0

Ohm's law

the current flowing through a conductor is proportional to the potential difference between its ends if the temperature remains constant.

Conductor

a medium that allows electric charge to flow through it easily

Insulator

a medium that does not allow electric charge to flow through it easily

Coulumb's Law

The electrostatic force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them

electric field lines

show the direction and strength of a force due to a positive charge in the field

electric field strength

the force that would be experienced per unit charge in an electric field

potential difference (voltage)

the work required to move a charge of 1C from one point to another

Capacitor

a device capable of storing an electrical charge

Electric current

the flow of electrons

Joule's law

The rate of heat produced in a constant resistance conductor is proportional to the square of the current

resistance

the ratio of the voltage across a conductor to the current flowing through it

Semiconductor

a material whose resistivity is between that of a good conductor and a good insulator

intrinsic conduction

conduction due to electrons and holes in a pure semiconductor material