PHYSICS MOD 5,6,8 COMPLETE

field

a region in which a body experiences a force due to the effects of another body. The effect can be the mass within the bodies, their charges or magnetic properties

work-energy theorem

the work done on a system is equal to its change in kinetic energy

the net work done by all forces acting on an object is equal to the change in its kinetic energy (if you do work on an object, it will change its energy)

Law of Conservation of Energy

In a closed system when energy is transformed from one form to another, the total amount of energy remains the same

work

displacement of an object moved parallel to a field

emf (electromotive force)

aka. voltage

the amount of energy that the battery gives to each coulomb of charge

electron volt

One electron volt (1eV) is the amount of energy gained (or lost) by the charge of a single electron moving across an electrical potential difference of one volt

magnetic field

a 3D region of space where a magnetic dipole will experience a force

magnetic flux (Φ - phi)

measured in Wb (weber) is a measure of the amount of magnetic field permeating a space

motor effect

where a current-carrying conductor (such as a wire) placed in an external magnetic field experiences a force

aka. Lorentz force

magnetic flux density (B)

the degree of concentration of flux

area vector (A)

a vector perpendicular to the plane of the area of the object in the field

flux linkage

is the total magnetic field lines passing through a multi-turn coil, calculated by multiplying the number of turns (N) in the coil by the magnetic flux (Φ)

galvanometer

a sensitive ammeter that allows measurement of current in two directions with a zero reading at the centre of the dial

Lenz’s Law

“the direction of the current induced in a conductor by a changing magnetic flux is such that the magnetic field created by the induced current opposes the initial changing magnetic flux.”

permeability (μ)

the measure of ease, with which mangetic lines of force pass through a given material — how easy it is for flux lines to pass through it

primary coil

the input coil which has an AC current running into it

secondary coil

the output coil

eddy currents

circular currents set up in the metal object near where the change in flux is occurring

produced in solid sheets or blocks of conductors (metals) and are produced at right angles to the direction of the changing flux → causes transformers to not be 100% efficient as the creation of these currents uses energy

torque

the turning moment of a force

motors

change electrical energy into mechanical, kinetic or potential energy

split-ring commutator

acts as a switching device to change the direction of the current in the coil every half rotation (uses DC)

armature

component of DC motor

the rotating core that converts electrical energy into mechanical energy

rotor coil(s)

component of DC motor

insulated copper wire wrapped around an iron core. When energized, these coils create an electromagnet that interacts with stationary magnets (the stator) to generate rotational force (torque)

brushes

component of DC motor

conductive components (usually made of carbon and copper) that transfer electrical current from the stationary power source to the spinning rotor (armature) through the commutator

axle

component of DC motor

an electric motor that connects directly to, or integrates with, a drive axle to turn wheels or mechanical parts

back emf (curly E)

The emf induced in opposition to the supply emf running the motor

AC generator

a device which converts mechanical energy into electrical energy → outputs power in the form of alternating voltage and current

slip ring commutator

an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires rotation while transmitting power or signals.

USED IN AC MOTORS/GENERATORS

DC generator

can be made from an AC generator by using a split-ring commutator rather than slip rings

can be made by using a bridge rectifier circuit which converts the AC output from the generator into DC output

turning mechanism

allow method/means to mechanically rotate the coil (in a generator)

stator windings

the electrical coils housed inside a stator (the stationary part of a rotary machine) → in an AC generator

AC induction motor advantages (over other types of motor)

• simple design (simple and cheap to construct)

• reliability - no brushes or commutators, little friction to wear parts down (which would need to be replaced over time)

• can be built to suit almost any industrial requirement

• are economical and efficient to run (for most purposes)

• polyphase induction motors are self-starting → when you turn AC source on, the motor starts (doesn’t require special starting means)

single-phase generator

produces electrical power using a single, continuously alternating voltage

multiphase generator

an electrical machine that converts mechanical energy into multiple alternating current (AC) waveforms

AC induction motor disadvantages (compared to other types of motors)

• only work on AC

• maximum speed is limited by the supply frequency (a 50Hz supply limits to 3000rpm)

• starting torque is low → they can’t get heavy loads moving very quickly

• not as efficient as some other AC motors when used in heavy industrial applications

classes of single-phase AC motors

• commutator motors

• synchronous motors

commutator motors

“Universal motors” can run on AC or DC electricity

the AC series motor - a specialized electric motor that incorporates a mechanical commutator and carbon brushes to operate on alternating current (AC) Unlike standard AC induction motors, these motors provide higher starting torque and operate at high speeds. They are primarily found in household appliances and power tools

synchronous motors

an AC electric motor in which the rotation of the shaft is perfectly locked in step with the frequency of the supply current (fixed frequency = constant speed that’s why they’re used in clocks and other similar devices requiring a constant rate of rotation)

Models of the atom

Dalton - Billiard Ball
J J Thomson - Plum Pudding
Rutherford - Nuclear model
Bohr - Planetary model
Chadwick - Neutrons in nucleus

cathode rays

beam of electrons

cathode ray experiments

1. gas discharge tubes

2. maltese cross

3. paddle wheel tube

4. curved fluorescent screen

5. addition of electric field between parallel plates

Gold foil experiment (Geiger-Marsden)

Rutherford disproved the "plum pudding" model of the atom

Milikan's oil drop experiment

find charge of e- by measuring stationary oil droplets and equating the magnetic field to the gravitational field to find the charge.

canal ray experiment (Goldstein)

mass of positively charged particles depends upon nature of gas.
q/m ratio of particles depend upon which gas the particles original

alpha particle experiment (Chadwick)

found neutrons in the nucleus

classical physics

physics before the Bohr model (before quantum physics and relativity)

Quantum mechanics

fundamental theory of physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles

Balmer series

A set of spectral lines that appear in the visible light region when a hydrogen atom undergoes a transition from energy levels n>2 to n=2.

Maxwell’s Theory of Electromagnetism

An accelerating charged particle will produce electromagnetic radiation (EM waves)

Limitations of the Rutherford Model of the Atom

• Couldn’t explain spectral lines and why a continous spectra wasn’t produced when excited electrons return to their original energy level

• Can’t explain why accelerating electrons don’t produce EM waves (Maxwell’s Theory of Electromagnetism) → atoms should be unstable based on this model but they are not

Spectral lines

dark or bright lines in a spectrum that correspond to specific wavelengths of light, created when atoms, molecules, or ions absorb or emit photons

obseservable spectra

• continuous spectrum

• emission spectrum 

• absorption spectrum

continuous spectrum

produced: when an incadescent light or sunlight is refracted through a prism

emission spectra

produced: when gas molecules are excited by putting a large DC voltage across them, in a vaccum. Resultant light is refracted through a prism or diffraction grating

result: bright, coloured, distinct lines are produced with a black background

absorption spectra

produced: when white light is passed through a pure gas before passing through diffraction grating or prism

result: spectrum is complete except for the presence of black bands in the same positions (for each gas) as the emission spectrum

Diffraction grating

we did pracs with this, an optical device with a periodic structure that separates light into its constituent wavelengths

Prism

used to refract light, separates into its constituent wavelengths

Bohr’s postulates

Postulate 1: Electrons in an atom exist in stable, circular orbits and these electrons in stable orbits do NOT emit radiation

Postulate 2: Electrons absorb or emit specific quanta of energy when they move from one stable energy level to another. E=hf (for EM waves)

Postulate 3: The electron’s angular momentum is quantised (don’t need to know more than this)

Plank’s quanta

energy of EM waves can be quantised and calculated using E=hf

Rydberg’s mathematical model for hydrogen’s spectral lines

1/𝜆 = R(1/n_f² - 1/n_i²)

Spectral lines → Law of Conservation of Energy

transition of electrons between orbits follows this Law: if an electron drops from a higher energy level to a lower energy level, the energy must be transformed.

Limitations of Bohr’s Model of the Atom

• only predicts hydrogen’s spectrum

• doesn’t explain why the lines in the spectrum vary in intensity/thickness and why some are sharp, dull thin and diffuse

• Can’t explain the ‘zeeman effect’ or the ‘anomalous zeeman effect’

• couldn’t explain why electrons didn’t emit radiation (same as Rutherford) and why they didn’t spiral towards the positive nucleus

The Zeeman Effect

Observed that when the spectrum of a sodium flame burning in a magnetic field was visualised → some lines split into 3 COULDNT BE EXPLAINED BY BOHRS MODEL

The Anomalous Zeeman Effect

Spectral lines could also split into 15 hyperfine lines when observed in a magnetic field. COULDNT BE EXPLAINED BY BOHRS MODEL

Diffraction

the spreading of wavefronts as they pass through a small aperture (small opening) or past an obstacle

Braggs Law

Used for when two reflected x-rays constructively intefere

n𝜆 = 2dsin𝜃

Constructive interference

a phenomenon where two or more waves combine to form a resultant wave with a larger amplitude

Destructive interference

a phenomenon where two waves combine to cancel each other out, resulting in a wave with a reduced or zero amplitude

De Broglie Hypothesis/The Theory of electron waves

“all moving matter exhibits wave-like properties and that the wavelength of this matter wave is inversely proportional to its momentum according to the equation: 𝜆 = h/p = h/mv

includes evidence from wave-particle duality theory of matter, Plank’s work and Einstein’s work on light (mod 7)  → as quanta were now accepted and the dual theory of light

standing waves

a wave pattern that oscillates in place without moving through space, appearing to "stand still” → De Broglie waves were this type

nodes

the points of the wave that do not vibrate

antinodes

the points that vibrate between maximum and minimum positions

de Broglian wavelengths

standing waves that allowed electron quantum states (shells) circumferences would always contain a multiple of these wavelengths (integer)

-→ used incrememnts to explain why certain energy levels were stable, ie. the ones that has an integer multiple of de Broglian wavelengths

equation:  C = n𝜆

— The stable orbits of the hydrogen atom are those where the circumference  is exactly equal to a whole number of electron wavelengths

Electron spin

Pauli Exclusion principle

• any atomic orbital (or other quantum state) can contain at most two electrons, and they must have opposite spin directions

• This means that no two electrons can have all four quantum numbers the same

No two electrons in a single atom can have the same set of four quantum numbers (applies to electrons, and all fermions)

Quantum numbers

Proposed in order to distinguish electrons in an atom from one another by considering 4 quantum numbers:

1. The energy level

2. Shape of the orbital

3. Orientation of the sub-orbital

4. Spin of the electron

NO TWO ELECTRONS COULD BE IDENTICAL

Heisenberg’s uncertainty principle

The more exactly we know a particle’s position, the less certain we become of its velocity (and momentum) and vice versa

“electron cloud” model of the atom (The Quantum mechanical model of the atom)

Schrodinger’s model of the atom → currently accepted model of atom

nucleon

the collective name for the two main subatomic particles in the nucleus; protons and neutrons

atomic number (Z)

number of protons in an atom

standard atomic weight

average weight of an element (considers that many elements have isotopes

mass number (A)

number of protons and neutrons

charge on an atom

results from a loss or gain of electrons

Strong nuclear force

the force that holds the nucleus together. it has properties of:

• acts only over small distances

• force is between nucleons (p→p, p→n etc.)

• at very close distances, nucleons repel each other (not a linear relation)

• at around 3×10^-15 m the strong nuclear force drops to zero

radioactive

way to describe a nuclide that emits some kind of radiation (if it is unstable)

radioactive decay

an unstable nuclide emits radioactive particles in process to become stable

nuclide

a specific type of atom defined by the exact number of protons and neutrons in its nucleus, and its energy state

3 ideas to predict nuclear stability

1. Neutron to proton ratio

2. The band of stability

3. Magic numbers

Transmutation

the change of one chemical element into another by nuclear decay or radioactive bombardment

spontaneous radioactivity

decay/emission of radioactive particles which is NOT caused by human intervention or accelerators

ionisation

removal of a bound electron from an atom to produce a free electron and a positive ion - THIS IS NOT RADIOACTIVE DECAY

radioisotopes

unstable atoms that emit particles that undergo nuclear reactions (decay) to become more stable

• daughter products have a greater binding energy per nucleon than the original parent nuclide

Decay series

It is called a ______ _____ when one radioactive isotope decays into another, and the daughter is also unstable and further decays occur until a stable nucleus is created

half life

the time it takes for half of a sample of a radioactive substance to undergo radioactive decay or the time required for the number of unstable atomic nuclei in a sample to decrease by half

hadrons

heavy, composite (made up of multiple quarks) that are affected by the strong nuclear force

• e.g. protons

leptons

fundamental particles (not made up of other particles) which are NOT affected by the strong nuclear force

• e.g. the electron, the muon

fundamental particles

particles which are not made up of other particles

elementary particles

fundamental particle that is not made up of any other particles

• e.g. quarks, electrons

composite particles

a particle that is composed of two or more elementary particles

quarks

an elementary particle that are the building blocks of hadrons and have a fractional charge , interact with the strong force and obey the Pauli Exclusion Principle