IB SL Physics Definitions + Things to remember!

Solar System

A collection of bodies that are gravitationally bound to the sun (planets

Galaxy

A collection of billions of stars

Galactic Cluster

A collection of galaxies held together by gravity

Stellar Cluster

A collection of stars held together by gravity

Constellation

A collection of stars which are not necessarily close together, and form a recognisable group

Single Star

A star not gravitationally bound by another

Astronomical Unit

The mean earth-sun distance

Light Year

The distance light travels in a year

Stellar Parallax

The apparent movement of a nearby object against the background as seen from two positions

Parallax Angle

The difference in angular positions

Luminosity

The total power output of a star (amount of energy radiated by a star per second)

Apparent Brightness

The power output per unit area at a given distance

Black Body

A perfect absorber and emitter of radiation

Wien's Law

The wavelength at peak intensity for a black body is inversely proportional to the surface temperature

Cepheid Variable

A star that varies in brightness over a period of days

Chandrasekhar Limit

Mass < 1.4M

Oppenheimer-Volkof Limit

Mass > 2.5M

Hubble's Law

There is a linear relationship between the recessional velocity of a galaxy and its distance

Critical Density

The density that will stop the expansion of the universe (value where universe will contract)

Cosmic Scale Factor 'R'

The relative expansion rate of the universe

Binding energy

The energy needed to completely separate a nucleus into its nucleons

Model of atom based on Rutherford's experiment

• Most of the mass of an atom is confined within a very small volume/nucleus

• All the positive charge is confined within a very small volume/nucleus

• Electrons orbit the nucleus in circular orbits

Systematic error

An error that is identical for each reading

Random error

Measurements are above and below the true value with equal probability

Directly proportional

A graph of 2 directly proportional quantities will be a straight line through the oirign

Linear

Produces a straight line graph

Inversely proportional

Y is proportional to 1/x or yx=constant

Precise

A high number of significant figures with a small spread of results

Accurate

Near true value

Vector

Quantity with magnitude and direction

Scalar

Quantity with magnitude only

Displacement

The distance moved in a stated direction (distance and direction from starting point)

Speed

Rate of change of distance (per unit time)

Velocity

Rate of change of displacement

Acceleration

Rate of change of velocity

Instantaneous speed/velocity

Change in distance/displacement divided by one particular instant of time

Average speed/velocity

Change in distance/displacement divided by time taken over a period of time

Trajectory

Shape of the path that a moving object makes in the air

Newton's 1st law

An object continues in uniform motion or a straight line, or at rest, unless a resultant external force acts on it

Newton's 2nd law

Force = mass x acceleration

Newton's 3rd law

If body A exerts Body B, then body B exerts an equal and opposite force on Body A

Equilibrium

No resultant force in any direction (translational); No resultant momentum at any point (rotational)

Linear momentum

Mass x velocity

Impulse

Force x time or change in momentum

Law of conservation of linear momentum

In an isolated system, momentum is constant

Work

Force x distance moved in direction of force

Kinetic energy

The energy a body possesses by virtue of its motion

Principle of conservation of energy

Energy cannot be created or destroyed, only transformed from one form to another

Inelastic collision

When there is a change in kinetic energy

Elastic collision

When there is no change in kinetic energy

Power

Rate at which energy is transferred (or rate at which work is done)

Efficiency

Ratio of useful energy to energy transferred

Temperature

A property that determines the direction of heat flow from two bodies in thermal contact. It measures average random kinetic energy of particles of a substance

Temperature in Kelvin

Celsius + 273

Kelvin (absolute temperature)

Proportional to average kinetic energy of particles

Thermal energy

Energy that is transferred by a temperature difference

Internal energy

Total potential energy + random kinetic energy in a substance

Thermal capacity

Amount of energy needed to raise temperature of object by 1 kelvin

Specific heat capacity

Amount of thermal energy needed to raise temperature of unit mass of a substance by 1 kelvin

Specific latent heat

Amount of thermal energy needed to change the state of unit mass of a substance at constant temperature

Mole

Amount of substance that contains same number of units that are in 12g of carbon-12 (6.022*10^23)

Molar mass

Mass of one mole of a substance

Avogadro's constant

Number of atoms in 0.012 kg of Carbon 12 (6*10^23)

Pressure

Normal force to an area per unit area

Ideal gas assumptions

Gas consists of a large number of molecules; molecules move with a range of speeds; the volume of the molecules is negligible compared with the volume of gas itself; the collisions of the molecules with each other and the container are elastic; molecules exert no forces on each other or the container except when in contact; the duration of collisions is very small compared with the time between collisions; the molecules obey Newton's laws

Rays

Show direction of energy transfer of a wave

Wave fronts

Highlight the part of a wave that is moving together (in phase)

Displacement (waves)

Distance any point on a wave has moved from it's undisturbed position

Amplitude

Maximum displacement from mean position

Period

Time taken for one complete oscillation

Frequency

Number of oscillations that take place per unit time

Wavelength

Shortest distance along a wave between the points that are in phase

Phase difference

Time difference by which one wave leads or lags another

Wave speed

Speed at which wave fronts pass a stationary observer

Intensity

Average amount of energy transported by a wave in the direction of wave propagation, per unit area per unit time

Principle of superposition

When 2 or more waves meet, the resultant displacement is the sum of individual displacements

Simple harmonic motion

Periodic motion in which the restoring force/acceleration is proportional to the displacement and in the opposite direction

Longitudinal wave

Oscillations parallel to direction of energy transfer

Transverse wave

Oscillations are perpendicular to direction of energy transfer

Polarised light

Light in which electric field vector vibrates in one place only

Electric potential difference

Between 2 points, is work done per unit charge to move a small positive charge between two points

Electric current

Rate of flow of electrical charge

Electromotive force (EMF)

Total energy difference per unit charge around the circuit (PD When no current flows in a circuit)

Electronvolt

Energy gained by an electron when moving through potential difference of one volt

Resistance

Ratio between potential difference across component/circuit and current through it

Ohm's law

When temperature is constant, the current through metallic conductor is proportional to potential difference across it

Volt

1 joule per coulomb

Electric field strength

Force per unit charge on a small positive test charge

Drift speed

Average speed attained by a particle due to an electric field

Kirchoff's laws

1. Current flowing towards a junction = total current flowing away from junction

2. Sum of EMF in any closed loop = sum of potential drops in the loop

Newton's Universal Law of Gravitation

Gravitational force between 2 point masses is proportional to the product of 2 masses and inversely proportional to their distance squared

Gravitational field strength

Force exerted per unit mass on small point mass at a location

Fuel

Source of energy in usable form

Stefan boltzmann law

Power per unit area emitted by a body is proportional to the absolute temperature ^4

Energy density

Energy obtained from unit volume

Specific energy

Energy obtained from unit mass

Emissivity

Ratio of energy emitted (per unit area) of a body to energy emitted by a black body of same dimensions at same temperature

Surface heat capacity

Energy required to increase temperature of 1 m^2 of surface by 1 kelvin

Critical mass

Minimum mass needed to sustain fission

Nucleon

Particle in the nucleus of an atom (proton or neutron)