P&W Flashcards
What is an order of magnitude?
It is a power of 10
State what is meant by the term “fermion”
A fermion is a matter particle
State what is meant by the term “boson”
A boson is a force mediating particle
Quarks are ______
fermions (i.e. matter particles)
Leptons are ________
fermions (i.e. matter particles)
List the 6 quarks
Up down strange charm top bottom
List the 6 leptons
electron, muon, tau, electron neutrino, muon neutrino, tau neutrino
List the 4 force mediating particles and their associated force
Photon (electromagnetic force), Z & W+- bosons (weak force), gluon (strong force)
Which force is missing from the Standard Model
Gravity
What is the standard model?
A model of fundamental particles and their interactions
What are hadrons made up of?
Hadrons are composite particles made of quarks
Baryons are a type of ________ and they are therefore made-up of ________
hadron, quarks
Mesons are a type of ________ and they are therefore made-up of ________
hadron, quarks
Baryons are made of _______ quarks
3
Mesons are made of…
a quark-antiquark pair
Describe beta decay and how it is evidence for the existence of the neutrino
beta decay is when a neutron turns into a proton, electron and an anti electron neutrino. The mass after beta decay was much smaller than could be accounted for by mass-energy conversion and pointed to the existence of a new particle, the neutrino
State what is meant by “anti-matter”
Every particle in the standard model has a corresponding anti-particle, identical in every way except charge. These particles are called “anti-matter”.
State one piece of evidence for the existence of antimatter.
When matter meets antimatter they annihilate
What do electric field lines show?
They point from positive to negative and show which way a positive test charge would move if it were to be placed in the field
Describe the process of drawing electric field lines
Imagine placing a small positive charge near the distribution of charges in question. Now imagine and draw which way it would move. Repeat this for evenly-spaced locations around the distribution
What do charged particles experience in an electric field?
An unbalanced force. They therefore accelerate
Opposite charges _____; like charges _____
Opposite charges attract like charges repel
State the definition of potential difference
Potential difference is a measure of the work done W in moving a charge Q against an electric field i.e. V=W/Q voltage is a measure of the energy per unit charge.
Magnetic field lines point from _____ to ______.
Magnetic field lines point from North to South.
Describe a method to determine the motion of charges particles in a magnetic field
- Point fingers in direction of field. 2. Point thumb in direction of velocity. 3. The deflection direction is given by the backhand direction for positive charges and the forehand direction for negative charges
Describe how a particle accelerator words
In a particle accelerator an electric field is used to change the particle’s speed (SQA word: accelerate) while it is most common to use a magnetic field to change the particle’s direction (SQA word: deflect). High energy collisions produce new particles.
State what is meant by “nuclear fission”
A big nucleus splits into two smaller nuclei, converting some mass to energy in the process
Describe how to tell if nuclear fission is spontaneous or induced
Induced is usually caused by neutron bombardment. Spontaneous has no trigger
Describe induced fission
A nucleus is forced to split by neutron bombardment.
How can you tell from a nuclear equation whether it describes spontaneous or induced fission?
A neutron will be present in the reactants for induced fission but absent for spontaneous fission.
How can you tell from a nuclear equation whether it shows fission or fusion?
If the equation is for fission, a nuclear species with larger mass number will split into two, each with smaller mass numbers. For fusion two lighter atomic species will join to make one heavier one.
State what is meant by “nuclear fusion”
Two lighter nuclei join to make a bigger nucleus, releasing energy by converting mass to energy in the process
How does the mass of the products of a nuclear reaction compare to the mass of reactants?
The products are less massive than the reactants. The difference in mass is converted to energy
What is required for nuclear fusion reactors and what problem does this create for the design of the reactor?
Fusion reactors require charged particles at a very high temperature (i.e. a plasma). The plasma is too hot to be contained by anything other than magnetic fields. A fusion reactor therefore must levitate the plasma in a magnetic field.
State one piece of evidence for the particle model of light
photoelectric effect
State one piece of evidence for the wave model of light
interference of light
Describe the photoelectric effect
Photons of high enough energy can eject electrons from the surface of a material (photoemission).
State what is meant by the term “work function”
The minimum energy required to cause photoemission (i.e. eject an electron from a metal)
State what is meant by “photoemission”
Photoemission is the ejection of electrons from a material by light
State what is meant by the term “threshold frequency”
Minimum frequency of incident photon required to cause photoemission
How is threshold frequency related to work function?
The threshold frequency is the minimum energy of photon required to cause photoemission. From this the work function may be calculated using E=hf
If one photon hits the surface of a material with energy greater than its work function how many electrons will be ejected?
1
Explain why positively charged metal plates will not show the photoelectric effect.
Positively charges plates have already had their electrons removed.
A photon with energy greater than the work function strikes a material. Where does the extra energy go?
Into the kinetic energy of the ejected electron
What is meant by the term “coherence”?
Coherence describes waves which have a constant phase relationship
When does constructive interference happen?
When waves meet exactly in phase i.e. peak to peak and trough to trough
When does destructive interference happen?
When waves meet exactly out of phase i.e. peak to trough and trough to peak
What happens during constructive interference?
Waves combine to make a maximum
What happens during destructive interference?
Waves cancel out to make a maximum
What is path difference?
The difference in the length of the paths taken by two waves
State the condition for constructive interference
path difference = mλ
State the condition for destructive interference
path difference = (m+1/2)λ
How do you calculate slit separation given the number of lines per mm on a diffraction grating?
Take the reciprocal of the number of lines per mm
What does θ represent in the grating equation?
The angle between the central maximum and the order under consideration
What does m represent in the grating equation?
Order number
State what is meant by “absolute refractive index”
Absolute refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in the medium
Refractive index is always greater than ____
1
How does refractive index change with frequency?
Refractive index increases as frequency increases i.e. higher frequencies refract more than lower frequencies
In the equation for refractive index, θ1 must be greater/less than θ2 to ensure refractive index is greater than 1
In the equation for refractive index, θ1 must be greater than θ2 to ensure refractive index is greater than 1
When going from air to glass, light bends towards/away from the normal and when going from glass to air it bends towards/away from the normal unless it travels along the ________
When going from air to glass, light bends towards from the normal and when going from glass to air it bends away from the normal unless it travels along the normal
Describe an experiment to measure the refractive index of a material
- Send light into the material 2. Measure angle of incidence (θ1) and angle of refraction (θ2) 3. Plot sin(θ2) against sin(θ1) 4. Gradient of line of best fit is refractive index n
State what is meant by the term “critical angle”
The critical angle θc of a medium is the angle of incidence inside the medium which results in a refracted angle of 90°.
State what is meant by “total internal reflection”
total internal reflection is the name given to the complete reflection of light when it travels from a more dense towards a less dense medium at an angle greater then the critical angle for the medium it is in. No light is transmitted externally into the less dense medium, hence the name total internal reflection.
State what is meant by “irradiance”
Irradiance is the power per unit area incident upon a surface
What is an inverse square law?
An inverse square law means that as one quantity increases the other will decrease as the reciprocal squared.
Describe how irradiance varies with distance from a point source?
irradiance follows the inverse square law i.e. if the distance is doubled (x2) then the irradiance will quarter
Describe the Bohr model of the atom
The Bohr model pictures electrons orbiting the nucleus at certain distances, like planets around the sun.
Describe how the Bohr model is related to energy levels
The Bohr model has electrons only occupying certain distances from the nucleus. The electron will have a different amount of energy at each particular distance. These different energies are called energy levels. Levels which are closer to the nucleus are lower in energy and those further away higher.
What is the “ground state”?
The lowest energy level which an electron can occupy
What is an “excited state”?
Any energy level above the ground state. When an electron occupies any level above the ground state is is said to be in an excited state
State what is meant by “energy levels”
Energy levels are particular values of energy which an electron can have. The electron cannot have any energy, it can only have energy corresponding to an energy level
What is chosen to be the zero of potential energy in the Bohr model?
When the electron is completely removed (i.e. ionised) from the atom. [Zero potential energy is defined as being at infinite distance from the atom. This means the electron is free from the electrostatic influence of the atom and therefore is given no potential energy by the atom.]
What is meant by the term “ionisation” in relation to the Bohr model of the atom?
Ionisation is when an electron is completely removed from an atom. This means it occupies no energy level and its potential energy is no longer negative.
What happens when an electron falls from a higher energy level to a lower one?
Light is emitted with energy equal to the difference in energy between the two levels. The frequency of light emitted can be calculated using E2 - E1 = hf
State what is meant by the term “emission line spectrum”
An emission line spectrum shows the wavelengths of light emitted due to electron transitions between particular energy levels
Describe how line emission spectra are produced
Exciteed electrons in an atom drop from higher energy levels to lower ones. As they do this, light is emitted at a frequency correspoinding to the difference in energy of each level. Light is only emitted at particular frequencies; each frequency is shown as a coloured line in an emision spectrum.
Describe how continuouus emission spectra are produced
Continuous emission spectra are produced when electrons drop between many energy levels with tiny differences between them e.g. in a hot solid such as the sun.
Describe how absorbtion spectra are produced
Absorption spectra occur when the electrons in an atom absorb specific energies of photons and the electrons move up to the relevant energy levels. An observer will see dark lines in a continuous emission spectrum corresponding to the absorbed wavelengths.
State what is meant by the term “Fraunhofer lines”
Fraunhofer lines in the continuous emission spectrum of the sun are evidence for the composition of its outer atmosphere.
