Module 6 Flashcards
What is a capacitor
2 metallic plates seperated by an insulator
Define dielectric
Insulator seperating 2 plates in a capacitor
How does a capacitor store charge
When the capacitor is connected to the cell, electrons flow from the cell.
The breif current means electrons are removed from plate A of the capacitor and deposited onto the other plate B. Plate A becomes positively charged (loss of electrons) and plate B becomes negatively charge.
What happens when a capacitor is charged
The plates have equal and opposite charge (Q) so there is a p.d. across the plates
When is the equation X=Xo (1-e^-t/RC) used
when X can be either V or Q
What type of current is the domestic supply
Alternating
What is smoothing capacitors
A diode is used to make an alternating current flow only in one direction
With a capacitor the output voltage is smoothed out
What is a feild
A region in which an object experiences a force
State coulombs law
Any 2 point charges exert an electrostatic force on each other that is directly proportional to the product of their charges and inversly proportional to the square of the distance between them
Similarities between electric feilds and gravitational feilds
Both are radial feilds
Both follow inverse square law
Differences between electric feilds and gravitational feilds
Gravitational feild is always attractive
For a charged particle in an electric feild how is the horizontal motion affected
No acceleration (constant v)
For a charged particle in an electric feild how is the vertical motion affected
Acceleration = F/m or EQ/m
Suvat can be used
How to find work done from force distance graph
Area underneath
Define electric potenitial
Electric potential at a point is equal to the work done per unit charge in bringing a positive charge from infinity to that point
Define electric potential difference
Work done per unit charge between two points around the particle of charge Q
What is an equipotential line
A line along which electric potential is the same
Where do magnetic feild lines act around the earth
From South of the earth to north
(north magnetic pole to south magnetic pole)
What rule determines the direction of a magnetic feild
Right hand grip rule
Define magnetic flux density
The strength of the feild
How does a velocity selector work
2 parallel horizontal plates connected to a power supply produces a uniform electric feild between the plates (strength E)
A unifrom magnetic feild (strength B) is applied perpendicular to the electric feild.
The charged particles travelling at different speeds can be sorted through a narrow slit.
Since electric and magentic fields deflect them in opposite directions, only particles witha a specific speed will the directions cancel out.
Only particles with this specific speed will pass through the second slit.
How does a mass spectrometer work
Only particles with the same velocity enter a unifrom magnetic feild
Each ion is deflected a different amount by the detector to fin mass
What is a hall probe
Used to measure magnetic flux density
Define magnetic flux
The product of the component of the magnetic flux density perpendicular to the cross sectional area.
Define magnetic flux linkage
The product of the number of truns in the coil and the magnetic flux
SI unit of flux linkage
Weber
State Faradays law
The magnitude of the incident emf is directly proportional to the rate of change of magnetic flux linkage
State Lenz law
The magnitude of the incident emf is inversely proportional to the rate of change of magnetic flux linkage
What is a step up transformer
Has mor turns on the secondarly coil than the first
What is a step down transformer
Has fewer turns on the secondary coil than the primary
Conclusion of ruthorfords alpha scattering experiment
Most of the alpha particles passed straight through so most of the atom is empty space with most of the mass concentrated in the nucleus
Alpha particles near th nucleas were repelled so the nucleus must be positively charged
What is an isotope
Nuclei of the same element that have a different number of neutrons
What is the nucleon number
Total number of protons and neutrons
What is the atomic number
Number of protons present
What is the atomic mass unit
1.66x10^-27 or 1 twelfth of the mass of a carbon 12 atom
What is the nuckear strong force
Attractive gravitational force between the protons (overcoming magnetic repulsion)
Under what range is the strong force attractive
0.5-3fm
What is the weak nuclear force
Responsible for beta decay
What are hadrons
Particles and antiparticles affected by strong nuclear force and weak nuclear force
Made up of quarks
(protons, neutrons and mesons)
Leptons
Particles and antiparticles unaffected by strong nuclear force
(electrons, neutrinos, muons)
What are the fundemental particles
Quarks and leptons
Types of quarks
up down strange charm top bottom
What are baryons
Hadroms made of 3 quarks
What are mesons
Hadrons made from quark antiquark pair
Beta minus decay
Neutron = proton + electron + electron antineutrino
Beta plus decay
proton = neutron + positron + electron neutrino
Explain alpha radiation
2 protons and 2 neutrons
highly ionising
not penetrating (stopped by a sheet of paper)
positively charged
Explain beta radiation
Fast moving electrons or positrons
stopped by 1-10mm of aluminium
positively and negatively charged depending on type
Explan gamma radiation
High energy photons
not very ionising
highly penetrating (stopped by 1-10cm of lead)
uncharged so unaffected by magnetic feilds
Define random
Cannot predict when next decay will be
each nucleus has equal chances of decaying per unit time
Define spontanious
Unaffected by presence of other nuclei in the sample
Unaffected by external factors such as pressure
Define half life
Time taken for number of active nuclei in a sample to half
Define activity
Rate at which nuclei decay
Define decay constant
Probibility of decay of an individual nucleus per unit time (A/N) (lambda in the booklet)
How does carbon dating work
Measuring ratio of carbon 14 to carbon 12 of dead material and similar living material.
What is annihilation
When a particle and antiparticle meet and their mass is turned into energy
Define mass defect
Difference between the mass of the completely seperated nucleaons and the mass of the nucleus
Define binding energy
Minimum energy required to completely separate a nucleus into its seperate protons and neutrons
what does high binding energy per nucleon
The more tightly bound the nucleons within the nucleus are
Define nuclear fission
An unstable uranium 235 nuclei splits into 2 halves after absorbing a nutron
Also releases more neutrons
What is a moderator used for in a fission reactor
Slow down fast paced neutrons
What is a control rod used for in a fission reactor
Material to absorb neutrons
What is nuclear fusion
Bring nuclei within 10^-15 fm so strong nuclear force becomes attractive
Has to be at high enough temperatures
What is thermionic emmision
emission of electrons througb heating at the cathode
What is the anode in an X ray
Target metal such as tungsten (high melting point)
Undergoes attenuation mechanisms
Define simple scatter
Range of 1-20keV
X ray photon bounces off
Define photoelectric effect in X rays
less than 100keV
X ray photon is absorbed and electron is released
Define compton scattering
0.5-5MeV
Electron is released and X ray released with reduced energy
Define pair production
> 1.02MeV
X ray dissapears and creates electron and positron
Define contrast medium
Elements with large atomic numbers so higher attenuation coefficient
Barium for digestive system
Iodine for blood flow
What is a CAT scan
Fan shaped beam of X rays absorbed at the other side by detectors
X rays attenuated by different amounts by different tissues
Fan complets 360 degrees and table is moved through the ring a bit more
Downsides of CAT scans
Ionising
expensive
time consuming
Positives of CAT scans
3D image
can distinguish between different tissues
What is a radioisotope
Gamma source w short half life placed inside the patient
Eg florine 18
What is a radiopharmecutical
Medical tracer which is a radioisotope made to reach the correct place
Concentrations can identify irregularities in the body
Define colimator
Honeycomb of long thin tubes
Any photons arriving at an angle are absorbed
Define scintillator
Produces viable light from incoming x ray photons
Define photomultiplier
Viable light from scintillator is multiplied into a voltage to be connected to a computer and modelled
What is a PET scan
Gamma radiation used to make 3d image
Use a medical tracer that our body thinks is glucose (flourodeoxyglucose)
Advantages of PET scan
3d image
non invasive
Disadvantages of PET scan
Expensive tracers and equipment
Ultrasound benefits
non ionising
non invasive
What is the peizoelectric effect
peizocrystel compressed and streched produces an alternating current and vice versa
The frequency of oscillation is the natural frequency of the crystal
Define transducer
used to detect ultrasound
What is an A scan
Simple ultrasound
Each pulse of ultrasound is partially reflected by different tissues which is recieved at the transducer and displayed on an oscilloscope
speed and time used to measure distance
What is a B scan
2D image
each position of transduce produces a row of dots which corresponds to a boundry
brightness of the dot is proportional to intensity of reflected ultrasound
computer can turn this into an image
What is coupling gel
gel with similar acoustic impedance to skin which stops relfections at skin boundry
(impedance matching)
What is a doppler ultrasound used for
track blood clots, movement of blood and speed
How does intensity effect realeased photon energy
It doesnt photon energy is inependent of intenisty
voltage in x rays
High voltage
Electrons thru graphite show what
electrons travel in waves
Current used in transformers
alternating
