G485 Definitions Flashcards
Define electric field strength
The electric field strength at a point is the force per unit charge exerted on a positive charge placed at that point
The electrical force experienced by an electron between parallel charged plates is given by the equation….
F = eV/d
State Coulomb’s law
Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them
The two units of electric field strength are…
NC-1 or Vm-1
We use Fleming’s LH rule
To predict the direction of the force on a charge carrying conductor placed in a magnetic field
We use Fleming’s RH rule
To predict the direction of the induced current in a conductor where there is relative movement between the conductor and a magnetic field.
The symbol B stands for
Magnetic flux density
The unit of magnetic flux density is
Tesla (T)
A charged particle moving at right angles to a uniform magnetic field will always travel…
In a circular path
For a charge q moving at right angles to magnetic field B what is the relationship between the momentum of the charged particle and the radius of its orbit?
The radius is directly proportional to the momentum (p=Ber)
Two devices which use r=mv/qB are
Mass spectrometers and particle accelerators
Magnetic Flux =
Magnetic flux density x Area
Magnetic flux linkage is defined as
The product of magnetic flux and the number of turns
Faraday’s law of electromagnetic induction is…
The magnitude of the induced e.m.f is proportional to the rate of change of magnetic flux linkage
Lenz’s law states….
That any induced current or e.m.f will be established in a direction so as to produce effects which oppose the change that is producing it.
A step up transformer
Increases voltage and reduces current
Define capacitance
Capacitance is the charge stored per unit of potential difference across it
The unit of capacitance is…
Farad (F)
An equivalent unit of the Farad is….
CV-1
The energy stored on a capacitor is given by
1/2QV
Decay is said to be exponential if….
A quantity reduces by a constant ratio in equal intervals of time
The time constant of a circuit is defined as….
The time taken for the current/charge/pd to fall to 1/e of its initial value
Time constant =
CR
Isotopes are…
Nuclei of the same element with different numbers of neutrons but the same number of protons
Hadrons are particles that
Are affected by the strong nuclear force
Two examples of hadrons are
Protons and Neutrons
Leptons are particles that
Are not affected by the strong nuclear force
An example of a lepton is
Electrons
Murray Gell Mann first proposed the idea of what in 1964?
Quarks
Composition of a proton in terms of quarks is
u u d
Composition of a neutron in terms of quarks is
u d d
Binding energy is defined as
The minimum energy needed to pull a nucleus apart into its separate nucleons
In a nuclear fission reactor which part slows down neutrons so that they are more likely to induce fission?
The moderator - usually graphite
In a nuclear fission reactor which part absorbs neutrons in order to slow down the chain reaction?
The control rods - usually boron
Name 3 coolants used in nuclear fission reactors
Water (PWR), Carbon dioxide (AGCR), Sodium
An alpha particle consists of
2 neutrons and 2 protons
A Beta - particle consists of
An electron
A Beta + particle consists of
A positron
Which particle associated with radioactive decay was discovered in 1956?
Neutrinos (and antineutrinos)
How do the nucleon and proton numbers change during alpha decay
Nucleon number decreases by 4. Proton number decreases by 2
How do the nucleon and proton numbers change during beta - decay
Nucleon number stays the same. Proton number increases by 1
How do the nucleon and proton numbers change during beta + decay
Nucleon number stays the same. Proton number decreases by 1
Define the decay constant
The probability that an individual nucleus will decay per unit time interval
Define the activity of a radioactive source
The rate at which nuclei decay
Define half life
The mean time taken for half of the nuclei in a sample to decay or
The mean time taken for the activity of a sample to reduce by half
X rays are produced when…
Fast moving electrons are rapidly decelerated
Three ways in which Xrays can be absorbed are…
Photoelectric effect, Compton scattering, Pair production
Half thickness is defined as…
The thickness of absorber which reduces the intensity of an X ray beam by half
Intensity is defined as
Power per unit cross sectional area
Two methods of improving X ray images are
Image intensifiers and Contrast media
Two advantages of CAT scans over X rays are…
They produce 3D images
They can distinguish between tissues of similar density
The order of components in a gamma camera is
Collimator, Scintillator, Photocathode, Photomultiplier, Computer
Radionuclides used in diagnostic medicine include…
Fluorine 18, Technetium 99, Iodine 123
PET stands for …..
Positron Emission Tomography
MRI stands for…
Magnetic Resonance Imaging
`MRI uses which type of non ionising electromagnetic radiation?
Radio waves
Advantages of MRI scans are….
No ionising radiation used
No moving mechanisms
Greater soft tissue contrast
Images easily computer enhanced in either 2D or 3D
Disadvantages of MRI scans are
Cannot be used on patients with metal implants.
Pacemakers affected.
Ultrasound is defined as ….
A sound with a frequency greater than 20,000Hz
Ultrasound can be produced and detected by ….
A piezoelectric crystal transducer
Acoustic impedance of a material =
density x speed of sound in material
Gel is used in ultrasound scans in order to…
To ensure impedance matching to avoid the ultrasound being reflected at the air-skin boundary
Doppler ultrasound is used…..
To monitor blood flow in the body
Name 4 stages in the life cycle of massive stars that do not occur in the life cycle of average stars.
Super Red Giant
Supernova
Neutron Star
Black hole (only the most massive stars)
The astronomical unit (AU) is
the average distance of the earth from the sun
~ 1.5 x 10(11) m
The definition of a light year is….
The distance travelled by light in a vacuum in one year
1 arc second =
1/3600 degrees
The parsec is defined as ….
The distance that gives a parallax angle of 1 arc second
State Hubble’s law
The speed of recession of a galaxy is directly proportional to its distance from earth
The hot big bang model is also known as
The standard model of the universe
