Physics Stuff Flashcards
Newtons first law?
An object in motion stays in motion, or an object at rest stays at rest, unless acted on by an external force
Newtons second law?
Force is directly proportional to change in momentum/time
Newtons third law?
If object a exerts a force on object b, object b exerts the sane force on object a
What is snell’s law
N1 sin(theta2) = n2 sin(theta2)
What is the area under a force time graph?
Impulse or change in momentum
What is the difference between an elastic and inelastic collision?
Kinetic energy is conserved in an elastic collision
How do you get percentage uncertainty of c if c = a b
Work out the percentage uncertainty of a and b and add them
How do you work out the percentage uncertainty of b if b = a^3 x c
Work out the percentage uncertainty of c and add it to 3x the percentage uncertainty of a
What is Kirchhoff’s 1st law?
Current flowing into a node is equal to the current flowing out of it
What is Kirchhoff’s 2nd law?
Sum of EMF = sum of voltage out
What is Coulomb’s law?
Two point charges exert a force on each other that is proportional to the product of the charges, and inversely proportional to the square of the distance
What is Faraday’s law?
Magnetically induced EMF is proportional to the rate of change of magnetic flux linkage
What is Lenz’s law?
The direction of the induced current is always such to oppose the change producing it (gives the -1 proportionality constant in Faraday’s law equation)
What is Kepler’s 1st law?
Planets move in elipses with the star at their focus
What is Kepler’s 2nd law?
Providing the time period between two sets of two points in a planet’s orbit is the same, the areas between star and each pair of planets is the same
What is Kepler’s 3rd law?
T^2 is proportional to r^3
What does an isotropic universe mean?
The universe looks the same no matter which direction you look
What does a homogenous universe mean?
Matter is distributed uniformly throughout the universe
What is accuracy?
Getting results close to the true value
What is precision?
Getting results that are close to each other
What is the initial stage of the universe?
The universe is a singularity, it is infinitely dense and hot
What is the first stage of expansion of the universe and when does it happen?
10^-35 seconds, inflation begins (the universe expands rapidly), the universe is full of high energy gamma photons
What is the second stage of expansion of the universe and when does it happen?
10^-6 seconds, the first fundamental particles form such as quarks and leptons
What is the third stage of expansion of the universe and when does it happen?
10^-3 seconds, quarks combine to form hadrons, most mass is created through pair production (gamma rays forming particle-antiparticle pairs).
What is the fourth stage of expansion of the universe and when does it happen?
100 seconds, protons and neutrons fuse to dorm deuterium and helium nuclei. Expansion is so rapid that no heavier elements are made.
What is the fifth stage of expansion of the universe and when does it happen?
380,000 years, the universe cool enough for full atoms to form as nuclei capture electrons. As a result, CMB radiation is formed.
What is simple scattering of X rays and at what energy does it occur?
The X ray interacts with the atoms and is scattered with no change in energy, up to 20keV
What is the photoelectric effect with regards to X ray scattering and at what energy does it occur?
The absorption of an X ray by an electron, which is then emitted, <100keV
What is Compton scattering of X rays and at what energy does it occur?
When an X ray removes an electron from an atom and is then scattered with reduced energy, between 0.5 and 5 meV
What is pair production of X rays and at what energy does it occur?
When an X ray photon interacts with a nucleus, disappearing in place of an electron and a positron, greater than 1.02 meV
Define the electric potential of a point in space?
The work done per unit charge bringing a positive charge from infinity to the point
What is hubble’s law?
Speed of recession of a galaxy is proportional to distance from earth
What is the definition of a parsec?
The distance from a base length of 1AU that subtends an angle of 1 arc second
What are the three main components of the gamma camera and what do they do?
- Collimator
Only allows gamma photons travelling parallel to the axis to pass through - Scintillator
Gamma photons are turned into light photons - Photomultiplier tubes
Light photons are converted into many electrons to be received by the computer
What is the limit for a star turning into a red giant Vs a red supergiant?
10 Solar Masses
What is the Chandrasekhar limit?
1.44 solar masses, the point at which the electron degeneracy pressure is not great enough to prevent a star’s core from collapsing into a neutron star
What is the limit for a star’s core forming a black hole?
3 Solar Masses
What is the limit of proportionality of a material?
The point at which the material stops obeying Hooke’s law
What is the elastic limit of a material?
The point at which a material begins to deform plastically
What are yield points of a material?
The turning points in a stress/strain graph, where the material extends rapidly
What is the ultimate tensile strength of a material?
The highest tensile stress a material can withstand before breaking, characterised by the highest point on a stress/strain graph
What is the breaking strength of a material?
The stress value at the point of fracture, characterised by the end of a stress/strain graph
What is the definition and the two requirements of simple harmonic motion?
Oscillating motion for which the acceleration is given by:
a = -ω^2 x
Where:
- Acceleration is directly proportional to displacement
- The acceleration is in the opposite direction to the displacement
What is an isochronus oscillator?
An oscillator in simple harmonic motion where the amplitude is independent of the time period
What scale is the nucleus of an atom on?
10^-14
What is Boyle’s law?
Pressure ∝ 1/Volume
What is Gay-Lussac’s law?
Pressure ∝ Temperature
What is Charles law?
Volume ∝ Temperature
What is Avagadro’s law?
Volume ∝ Moles
What is drag proportional to?
V^2 and area
At what range is the strong nuclear force attractive?
Up to 3fm
At what range is the strong nuclear force repulsive?
Less than 0.5fm
What is the force responsible for beta decay?
The weak nuclear force
What is the decay equation for a down quark?
d -> u + electron + anti neutrino
What is the decay equation for an up quark?
u -> d + positron + neutrino
What is the wavelength range for radio waves?
> 10^-1m
What is the wavelength range for microwaves?
10^-3 - 10^-1m
What is the wavelength range for infra red?
7x10^-7 - 10^-3m
What is the wavelength range for visible light?
4x10^-7 - 7x10^-7m
What is the wavelength range for ultra violet?
10^-8 - 4X10^-7m
What is the wavelength range for X rays?
10^-10 - 10^-8m
What is the wavelength range for the overlap between gamma rays and x rays?
10^-13 - 10^-10m
What is the wavelength range for gamma rays?
<10^-13m
What two contrast media are used for x rays? Why?
Barium and iodene due to their large atomic number (attenuation coefficient is proportional to atomic number ^3)
Advantages of CAT scans over x rays?
- 3d image
- can more easily distinguish between soft tissues
Disadvantages of CAT scans over x rays?
- Longer and more expensive
- Leads to longer ionising exposure
- Movements from the patient can blur the slice
What is a medical tracer or radiopharmaceutical? Examples?
A radioisotope combined with other chemicals to ensure it reaches the target organ. Fluorine-18 (beta plus) and Technetium-99m (gamma)
How are x rays produced (short answer)
The deceleration of electrons
How are x rays produced (long answer)
Connecting a heater to a high voltage power supply, producing fast moving electrons through thermionic emission. These travel through a vacuum (so they don’t interact with air) to the target metal (such as tungsten), where they hit it and are decelerated, producing an x ray
What is intensity proportional to?
Amplitude^2
