QCE Physics Unit 3+4
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169 Terms
What is the work function?
The minimum energy required to remove an electron from the surface of a metal. (symbol, 𝑊; SI unit, J)
What is the weak nuclear force?
One of the four fundamental forces; the weak nuclear force is responsible for radioactive decay and is mediated by W and Z bosons
What is the wave model of light?
The theory that light has the characteristics of waves such as wavelength, frequency and speed. Used to describe the behaviour of light such as interference and refraction.
What is uniform circular motion
The movement of an object at a constant speed around a circle with a fixed radius
What is time dilation?
The difference of elapsed time between two events as measured by observers moving relative to each other
What is the strong nuclear force?
One of the four fundamental forces; the strong nuclear force acts over small distances in the nucleus to hold the nucleons together against the repulsive electrostatic forces exerted between the protons; the strong nuclear force is mediated by gluons
What is simultaneity?
The relation between two events assumed to happen at the same time in a frame of reference
What is rest mass?
The mass of an object when measured in the same reference frame as the observer
What is relativistic mass?
The increased mass of an object moving at high speed
What is relativistic length?
The length measured in the frame of reference in which the object is in motion
What is relativistic momentum?
The momentum of an object when measured in the frame of reference in which the object is in motion?
What is the relativistic time interval?
The time interval measured in the frame of reference in which the object is in motion
What is radiation?
The emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles, which cause ionisation.
What are quarks?
Subatomic particles governed by the strong nuclear force that constitute hadrons.
What are the six quarks?
up, down, charm, strange, top, bottom
What is proper length?
The length measured in the frame of reference in which the object is at rest.
What is the proper time interval?
The time interval measured in the frame of reference in which the object is at rest.
What are the two postulates of special relativity?
The first postulate states that the laws of physics are the same in all inertial frames of reference; the second postulate states that the speed of light in a vacuum has the same value c in all inertial frames of reference.
What is Plank's constant?
A fundamental constant used in quantum mechanics (symbol, h; SI unit, Js) 6.626 x 10^-34 Js
What is a photon?
A quantum of all forms of electromagnetic radiation; a gauge boson responsible for mediating the electromagnetic force.
What is Ohm's Law?
A law that states that electric current is proportional to voltage and inversely proportional to resistance
What is Newton's law of universal gravitation?
The force of attraction between each pair of point particles that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
What are mesons?
Subatomic particles composed of one quark and one antiquark
What is magnetic flux?
A measurement of the total magnetic field that passes through a given area; a measure of the number of magnetic field lines passing through the given area (symbol, 𝜙; SI unit, Wb)
What is magnetic flux density?
the strength of a magnetic field or the number of magnetic field lines per unit area
What is a magnetic field?
A region of space near a magnet, electric current or moving electrically charged particle in which a magnetic force acts on any other magnet, electric current or moving electrically charged particle
What are leptons?
Particles that are governed by the weak nuclear force and, since they have charge, are also influenced by electromagnetism
What are the six leptons?
electron, muon, tau, electron neutrino, muon neutrino, tau neutrino
What is the lepton number?
a conserved quantum number defined by 𝐿 = 𝑛𝑙 − 𝑛𝑙̅, where 𝑛𝑙 is the number of leptons and 𝑛 ̅ is the number of antileptons
What is Lenz's law?
The law that the direction of an induced electric current always opposes the change in the circuit or the magnetic field that produces it
What is length contraction?
The observed decrease in length of an object which is moving at high speeds from an observer at rest relative to the moving object
What is Kepler's first law?
All planets move about the Sun in elliptical orbits, having the Sun as one of the foci
What is Kepler's second law?
A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time
What is Kepler's third law?
The squares of the sidereal periods of the planets are directly proportional to the cubes of their mean distance from the Sun
What is an inertial frame of reference?
Any frame of reference with respect to which the acceleration of the object of observation remains zero
What is a gravitational field?
The region of space surrounding a body in which another body experiences a force of gravitational attraction
What is gravitational field strength?
The net force per unit mass at a particular point in the gravitational field
What is a gauge boson?
Carrier or exchange particles that govern particle interaction and the mediation of the four fundamental forces
What are the four gauge bosons?
The gluon, photon, Z boson and W boson
What are the four fundamental forces, and what is their order from strongest to weakest?
One of four forces that act between bodies of matter and that are mediated by one or more particles;
They are, in order from strongest to weakest: the strong nuclear, the electromagnetic, the weak nuclear and the gravitational force
What is a frame of reference?
The abstract coordinate system that defines location of the observer
What are Feynman diagrams?
Graphical representation of particle interactions showing time along the horizontal axis and space along the vertical axis. The axis may be reversed, however not in this syllabus
What is Faraday's Law
A law stating that when the magnetic flux linking a circuit changes, an electromotive force (𝑒𝑚𝑓) is induced in the circuit proportional to the rate of change of the flux linkage
What are elementary particles?
A particle whose substructure is unknown (protons, neutrons, electrons)
What is the electromotive force?
A difference in potential that tends to give rise to an electric current, also written as 𝑒𝑚𝑓
What is electromagnetic radiation?
Radiant energy consisting of synchronised oscillations of electric and magnetic fields, or electromagnetic waves, propagated at the speed of light in a vacuum
What is electromagnetic induction?
The production of an electromotive force (EMF) or voltage across an electrical conductor due to its dynamic interaction with a magnetic field
What is the electromagnetic force?
One of the four fundamental forces; the electromagnetic force is mediated by photons
What is electric potential energy?
The capacity of electric charge carriers to do work due to their position in an electric circuit
What is electric potential difference?
The change in potential energy per unit charge between two defined points in a circuit; the unit of electrical potential difference is volts 𝑉; sometimes referred to as the voltage
What are electric fields
Regions around an electrically charged particle or object within which a force would be exerted on other electrically charged particles or objects
What is electric field strength?
The intensity of an electric field at a particular location
What is electric current?
The rate of movement of electric charge carriers from one part of a conductor to another
What is electric charge?
A physical property of an object that causes it to experience a force when placed in an electromagnetic field
What is Coloumb's law?
A law stating that like electric charges repel and opposite electric charges attract, with a force proportional to the product of the electric charges and inversely proportional to the square of the
distance between them
What is centripetal force?
A force that acts on a body moving in a circular path and is directed toward the center around which the body is moving.
What is centripetal acceleration?
The acceleration experienced by any object moving in a circular path directed towards the centre of motion
What is black body radiation?
The radiation emitted by a black body from the conversion of thermal energy; a black body is a perfect absorber or emitter of radiation
What is the baryon number?
A strictly conserved additive quantum number of a system
What is an antiparticle?
A particle with the same mass and opposite charge and/or spin to a corresponding particle, for example positron and electron
What happens when two electrons collide
When two electrons collide a photo is exchanged and they change directions
Baryon and Lepton numbers are…?
Conserved in all particle interactions
What happens when a neutron decays into a proton?
A down quark is turned into an up quark and a W boson is released.
What happens when a electron and a positron annihilate
Their mass is converted into energy in the form of a photon which then produces an electron and positron
What is the significance of symmetry in particle interactions?
Symmetry is when a particle interaction is subjected to a certain operation and it appears exactly the same after the operation (e.g. Charge, Time, Crossing)
Significance: (1) allows physicists to predict (as usually upheld by nature), (2) energy and momentum are conserved, (3) if not upheld, then not a universal law and allows for further investigation
What was Young's double slit experiment?
A single light source is directed towards two slits, which each act as a coherent light source, the light interferes constructively and destructively to create an interference pattern which provides evidence for the wave-model of light.
Back Body Radiation..?
Provides evidence that electromagnetic
radiation is quantised into discrete values
What is light?
An electromagnetic wave produced by an oscillating electric charge that produces mutually perpendicular oscillating electric fields andmagnetic fields
What is the mass energy equivalence relationship?
E=mc^2
Why can no objects travel at the speed of light in a vacuum?
As an object approaches light speed, it has to provide more and more energy to make it move. In order to reach the speed of light, it'd need an infinite amount of energy
How do transformers work?
AC passes through the primary winding, which creates a varying magnetic flux. The magnetic field that results strikes the second winding and generates an AC voltage in that winding via electromagnetic induction.
How is a magnetic field generated?
A magnetic field can be generated from a moving electric charge
What is a solenoid?
A coil of current-carrying wire that produces a magnetic field
What is the right hand rule?
Thumb points along the direction of the current. Other fingers give the direction of the field.
What is the right hand slap rule?
How can Kepler's third law be derived?
Kepler's third law can be derived from the relationship between Newton's Law of Universal Gravitation and uniform circular motion
What is the normal force?
The support force exerted upon an object that is in contact with another stable object
What is Rutherford's atomic model?
The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun
What are the limitations of Rutherford's model?
Could not explain the stability of the atom
Particles moving around the nucleus should give off energy and fall into the nucleus
Failed to account for hydrogen emission spectra
Describe Bohr's atomic model
Protons and neutrons in the nucleus with electrons in orbitals or energy levels orbiting around.
How does Bohr address the limitations of Rutherford's model?
Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another.
Explain how the Bohr model of the hydrogen atom integrates light quanta and atomic energy states to explain the specific wavelengths in the hydrogen line spectrum
By assuming that the electron moved in circular orbits and that orbits with only certain radii were allowed. Lines in the spectrum were due to transitions in which an electron moved from a higher-energy orbit with a larger radius to a lower-energy orbit with smaller radius. The orbit closest to the nucleus represented the ground state of the atom and was most stable; orbits farther away were higher-energy excited states. Transitions from an excited state to a lower-energy state resulted in the emission of light with only a limited number of wavelengths. Atoms can also absorb light of certain energies, resulting in a transition from the ground state or a lower-energy excited state to a higher-energy excited state. This produces an absorption spectrum, which has dark lines in the same position as the bright lines in the emission spectrum of an element.
What is evidence for the particle model of light?
The photoelectric effect: introduced evidence that light exhibited particle properties on the quantum scale of atoms