IB Physics HL Definitions (copy)

Newton's First Law

An object continues in uniform motion in a straight line/ at rest unless a resultant force acts.

Newton's Second Law

The acceleration of an object is proportional to and in the same direction as its resultant force.

Newton's Third Law

When 2 objects react, the exert equal and opposite forces on each other.

Elastic Collision

KE is conserved and objects bounce off with the same speed it did before in opposite directions.

Inelastic Collision

Maximum loss of KE, objects stick together & momentum is still conserved.

Mole

Amount of substance that has the same number of molecules as the number of of molecules as the number of atoms in 12g of C-12.

Avogadro's Constant

Number of molecules in 1 mole = 6.022 × 10²³

Specific Heat Capacity

The energy needed to increase the temperature of of 1 kilo of an object by 1K.

Specific Latent Heat

Amount of heat needed to change the state of 1 kilo of a substance WITHOUT a change in temperature.

Huygens’s principle

Every point on a wavefront is a source of wavelets that spread out in the forward direction at the same speed as the wave itself. The new wavefront is a line tangent to all of the wavelets.

Simple Harmonic Motion

Motion where the acceleration of an object is proportional to & in the opposite direction to displacement. a = -ω2x

Principle of superposition

When 2 or more waves of the same type meet, the total displacement at a point on a wave is the displacements of the individual waves added at that point.

Electric potential difference

Work done per unit charge in moving a positive charge from one point in the (electric) field to another.

Electronvolt

The amount of energy an electron gains by moving through a potential difference of 1 volt.

Electric current

The rate of flow of electrical charge.

Resistance

The ratio of voltage across the material to the current flowing through it.

Ohm's Law

The current through a wire is proportional to the p.d. across it; as long as the temperature is constant.

Electromotive force (emf)

The power supplied by the supply per unit current.

Gravitational field strength

The force per unit mass experienced by a small test mass placed in the field.

Newton's universal law of gravitation

Any point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to their separation².

Electric field strength

The force per unit charge experienced by a small test charge placed in the field.

Nuclide

An atom with a particular nucleus configuration.

Nucleon

A proton or a neutron.

Isotope

An element with the same number of protons but a different number of neutrons.

Radioactive half life

The time taken for the total number of nuclei (of a radioactive substance) to halve.

Unified atomic mass

The mass of ½ of the nucleus of a C-12 isotope.

Mass defect

The difference in mass between a nucleus and its separate nucleons.

Binding energy

The energy needed to break up a nucleus into its constituent nucleons.

Moderator

Slows down fast neutrons to increase the chance of more reactions. (So they don't pass through the nuclei)

Control rod

This absorbs neutrons to control chain reactions.

Heat exchanger

This allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. The thermal energy is transferred to heat water, and the steam that is produced turns the turbines.

Photovoltaic cell

Light hits semiconductors & electrons are released/ moved; creating an electric field.

Solar heating panel

Heat goes through glass pane & is absorbed by black pipes with running water in them.

Albedo

The ratio of reflected: incident radiation.

Emissivity

The ratio of power emitted by a body to the power emitted if it was a black body.

Gravitational potential

Work done per unit mass in bringing a test mass from infinity to that point in the field.

Electric potential

The work done per unit charge in bringing a positive test charge from infinity to that point in the field.

Standing waves

Transfer no energy. They have the same amplitude and are in phase. Happens when a wave & its reflection interfere (or just 2 waves)

Doppler Effect

The change in perceived frequency because the source or observer is moving.

Rayleigh criterion

2 points will be resolvable if the first minimum of the diffraction pattern of one source overlaps the central maximum of the diffraction pattern of the second source.

Eddy currents

tiny currents created in the core because the free electrons of the core move in the presence of a magnetic field.

Magnetic flux

A measure of the strength of a magnetic field over a given area/ number of field lines.

Magnetic flux linkage

The product of the magnetic flux and the number of turns in a given coil.

Faraday's law

The size of an induced emf is proportional to the rate of change of flux linkage.

Lenz's law

The direction of an induced current is such that it'll oppose the change causing it.

de Broglie Hypothesis

All particles have a wave like nature.

Electron in a box model

An electron has possible wavelengths like a standing wave on a string so electrons have discrete energies.

Schrödinger's model

This gives the probability of where the electron could be (probability regions called orbitals).

Heisenberg uncertainty principle

You can only know 1 from each pair:
-momentum & position
-energy & time

Decay constant

Probability of decay of a nucleus per unit time

Radioactive decay law

The activity of a radioactive sample ∝ Number of radioactive nuclei present.

Capacitance

Charge per unit p.d. that can be stored on a capacitor.

Stellar cluster

A group of stars that are physically near each other in space.

Constellation

A pattern of stars as seen from Earth that aren't physically near each other in space.

Light year

The distance that light travels in 1 year.

Luminosity

The total power emitted by a star.

Apparent brightness

The power received per unit area on Earth by a star.

Cepheid

A slightly unstable star that has a regular variation in brightness and luminosity due to a periodic expansion and contraction in its outer layers.

Red giant

-Red
-Comparatively cool
-Large
-Fuse elements other than Hydrogen

The Chandrasekhar limit

it is impossible for a white dwarf to have a mass greater than 1.4M_☉

Red Supergiant

-Red
-Large Mass
-Large Surface Area
-Large Luminosity
-Low Surface Temperature

White Dwarfs

-Very Small/ Low Surface Area
-Large Surface Temperature
-White

Visual Binary

Stars can be distinguished using a telescope

Parsec

A unit of distance that is equal to 3.26 light years

Critical density

The theoretical density of the universe that would create a flat universe.

Hubble's Law

The recessional velocity of a galaxy ∝ its distance away from Earth.

Jeans criterion

Jean's criterion for gas to collapse to form at star is simply that the magnitude of the potential energy of the gas must be greater than the kinetic energy of the gas. GM²/R > 3/2NkT

• s-process

• Slow neutron capture

• Heavy nuclides up to  Bismuth-209

• Stars will a small production of neutrons as a by-product of making carbon, oxygen, and silicon

• Nuclides have time to undergo beta-decay before they undergo neutron capture again

• Produces heavier isotopes of the original element

• r-process

• Rapid neutron capture

• Form elements heavier than Bismuth-209

• There is insufficient time for beta-decay before they undergo neutron capture again

• Occurs in stars that produce a lot of neutrons, such as a Type II supernova

Density Parameter(Ω_o)

the ratio of the actual density of the universe and the critical density of the universe

 

Evidence for dark matter

• Velocities of galaxies orbiting each other in clusters-these galaxies emit far less light than they ought to in relation to the amount of mass suggested by their velocities

• X-ray images of elliptical galaxies show the presence of haloes of hot gas extending well outside the galaxy. For this gas to be bound to the galaxy, the galaxy must have a mass far greater than that observed - up to 90% of the total mass of these galaxies is likely to be dark matter

dark matter 1

MACHOs(Massive Compact Halo Objects)

• Black holes, neutron stars, and small stars such as brown  dwarfs

• High mass objects

• Difficult to see when not near a luminous object

• Questionable if there are enough of these objects to account for dark matter

Dark Matter 2

WIMPs(Weakly Interacting Massive Particles)

• Subatomic particles that are not made up of ordinary matter(non-baryonic)

• Pass through matter with very little effect

• Particles don't have very much mass individually

• There would need to be a lot of them to account for dark matter

• Theory relies on hypothetical particle called axions and neutralinos which have yet to be discovered