Definitions I find super important Flashcards
N1L
An object continues in its state of rest or constant velocity in the absence of an external resultant force.
N2L
The rate of change of momentum of an object is directly proportional to the external resultant force acting on it, and the change in momentum takes place in the direction of the external resultant force.
N3L
When object A exerts a force on object B, then object B exerts a force of the same type that is equal in magnitude and opposite in direction on object A.
Inertia
The property of a body associated to its mass which is a measure of the body’s resistance to change in its state of rest or uniform motion in a straight line.
Linear momentum
The product of an object’s mass and velocity
Principle of Conservation of Momentum
The Principle of conservation of linear momentum states that the total momentum of a system of interacting bodies is constant provided no external resultant force acts on the system.
Elastic collision
Total momentum and total KE are the same before and after the collision, and relative velocity of approach equals relative velocity of separation.
Equilibrium
1) No resultant force acting on the body in any direction
2) No resultant torque acting on the body about any point
Moment of a force
The product of the magnitude of the force and the perpendicular distance of the line of action of the force to the point.
Torque of a couple
The torque of a couple is the product of one of the forces and the perpendicular distance between the forces, where a couple is a pair of forces equal in magnitude but acting in opposite directions, whose lines of actions are parallel but separate.
Principle of Moments
When a system is in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anti-clockwise moments about the same point.
Newton’s Law of Gravitation
Newton’s law of gravitation states that the gravitational force of attraction between two points masses is directly proportional to the product of their masses and inversely proportional to the square of the separation between their centres.
Geostationary orbit
An equatorial orbit with an orbital period of 24 hours and moves in the direction from West to East.
Gravitational field
A region of space in which a mass will experience a non-contact force.
Gravitational field strength
The gravitational force per unit mass experienced by a small test mass placed at that point.
Gravitational potential energy
Work done on the mass in moving it from infinity to that point.
Gravitational potential
The work done per unit mass in bringing a small test mass from infinity to that point.
Free oscillations
Oscillating system where there is no energy gain or loss
Forced oscillations
Continual input of energy by an external applied force to an oscillating system to compensate the loss due to damping in order to maintain the amplitude of the oscillation.
Damped oscillation
Oscillation in which there is a continuous dissipation of energy to the surroundings such that the total energy in the system decreases with time, hence the amplitude of the motion progressively decreases with time.
Simple harmonic motion
Oscillatory motion of a particle whose acceleration is directly proportional to its displacement from a fixed point and this acceleration is always in opposite direction to its displacement.
Phase difference
A measure of how much one wave is out of step with another, measured in either degrees or radians.
Resonance
Resonance occurs when the driving frequency of the external driving force equals to the natural frequency of the system, causing the resulting amplitude of the system to become a maximum.
Wavelength
The minimum distance between any two points of the waves with the same phase at the same instant.
Progressive wave
A wave in which energy is carried from one point to another by means of oscillations within the waves.
Transverse waves
Vibrations are in a plane normal to the direction of transfer of energy of the wave.
Longitudinal waves
Vibrations are parallel to the direction of energy of the wave.
Polarisation
Vibrations of the wave are in one direction of the plane normal to the direction of the transfer of energy of the wave.
Electric field
A region of space in which a force acts on a stationary charge, and the direction of electric field is in the direction of force on a positive charge
Electric field strength
The electric force per unit positive charge experienced by a small stationary test charge placed at that point.
Electric force/ Coulomb’s Law
Coulomb’s Law states that the electric force acting between any two point charges is directly proportional to the product of the charges and inversely proportional to the square of their separation. The direction of the force is along the line joining
the two point charges
Electric potential energy of a charge at a point
Work done in moving a charge from infinity to that point.
Electric potential
The work done per unit positive charge in moving a small test charge from infinity to that point.
Thermal equilibrium
When two objects in thermal contact are in thermal equilibrium, there is no net heat transfer between them, they are at the same temperature.
Ideal gas
An ideal gas is a hypothetical gas that obeys the equation of state pV = nRT perfectly for all pressure p, volume V, amount of substance n and temperature T.
Internal energy of a substance
The internal energy of a substance is the sum of the kinetic energy due to the random motion of the molecules and potential energy due to intermolecular forces of attraction
Internal energy of an ideal gas
Sum of the kinetic energy due to the random motion of the molecules only
First Law of Thermodynamics
The First Law of Thermodynamics states that the increase in the internal energy of a system is equal to the sum of the thermal energy supplied to the system and the external work done on the system.
Specific heat capacity
The quantity of thermal energy required per unit mass per unit temperature rise.
Specific latent heat of fusion
The quantity of thermal energy required per unit mass when
the substance changes from solid state to liquid state without a change in temperature.
Principle of superposition
When two or more waves of the same kind meet at a point at the same time, the displacement of the resultant wave is the vector sum of the displacements of the individual waves at that point at that time.
Diffraction
The spreading of waves at an edge or through a slit so that the waves do not travel in straight lines
Coherence
Waves are coherent if they have constant phase difference.
Stationary waves
When two progressive waves of the same type of equal amplitude, equal frequency, equal wavelength and equal speed travelling in opposite directions meet and undergo superposition with each other, a stationary wave is formed.
Antinode
A point on a stationary wave vibrating with maximum amplitude
Rayleigh’s criterion
For diffraction patterns to be just resolved, the central maximum of
one pattern must lie on the first minimum of the other pattern
Electric current
The rate of flow of charge
Potential difference
The p.d. across two points in a circuit is the work done per unit charge when electrical energy is transferred to non-electrical energy when the charge passes from one point
to the other.
E.m.f.
The e.m.f of a source is work done per unit charge when non-electrical energy is transferred into electrical energy when the charge is moved round a complete circuit.
Magnetic flux density
The magnetic flux density of a magnetic field is defined as
the force per unit length per unit current acting on a straight conductor placed normal to the field.
Faraday’s Law
States that the magnitude of the induced e.m.f. is directly
proportional to the rate of change of the magnetic flux linkage
Lenz’s Law
States that the induced e.m.f. or current is in a direction
so as to produce effects which oppose the change in
magnetic flux linkage
RMS value of an ac
RMS value is the value of the steady direct current which would dissipate heat at the same average rate in a given resistor
Photon
A discrete packet of energy of electromagnetic radiation. The energy of one photon is directly proportional to the frequency of EM radiation.
Photoelectric effect
The emission of electrons from a cold metal surface when EM radiation of sufficiently high frequency falls on it
Work function
The minimum energy of a photon to cause emission of electrons from the surface of the metal
Threshold frequency
The lowest frequency of electromagnetic radiation that gives
rise to the ejection of electrons from the metal surface.
de Broglie wavelength
Wavelength associated with a particle that is moving
Mass defect
The difference in mass between the mass of a nucleus and the total mass of its constituent nucleons.
Nuclear binding energy
The energy required to completely separate the nucleons in a nucleus to infinity
Binding energy per nucleon
The energy per nucleon required to completely separate the nucleons in a nucleus to infinity
Nuclear fission
Nuclear fission is the splitting of a nucleus of high nucleon number and low binding energy per nucleon into 2 smaller nuclei of approximately the same mass with higher binding energy per nucleon with the release of energy and neutrons.
Nuclear fusion
Nuclear fusion is the combining of two nuclei of low nucleon number to produce a larger nucleus with a greater binding energy per nucleon with the release of energy.
Radioactivity
Radioactivity is the spontaneous and random disintegration of the unstable nucleus, emitting some or all of the following nuclear radiations: alpha particles, beta particles and gamma radiations.
Spontaneous decay
Decay that is unaffected by external or environmental factors
Random decay
Nucleus has a constant probability of decay per unit time, and the time of decay of a nucleus cannot be predicted
Activity
The number of nuclear disintegrations per unit time of the nuclei
Decay constant
The constant probability of decay per unit time of a nucleus
Half life
Average time taken for the initial number of nuclei of that particular radioactive nuclide to reduce to half of its initial value
Background radiation
The radiation detected by a radiation counter when there is no radioactive source nearby
Count rate
Rate at which emissions from a radioactive source are emitted
Observations of Rutherford’s experiment
1) Most of the alpha particles were deviated through small angles or undeflected
2) A small but significant percentage of the alpha particles deviated through large angles greater than 90 and up to 180
Inference of most of the alpha particles were deviated through small angles or undeflected
For the structure of the atom, the nucleus exists and the size of the nucleus is small compared to the atom
Inference of a small but significant percentage of the alpha particles deviated through large angles greater than 90 up to 180
For the structure of the atom, the nucleus is charged and the mass is concentrated in the nucleus.
Radioactive decay of an unstable nucleus
The emission of alpha, beta, and/or gamma ray photons with the release of energy and the formation of a more stable nucleus.
Penetrating ability of alpha particles + Range in air + Ionising strength + Typical energy
Stopped by a piece of paper
~1 to 3cm
Strong
Characteristic emissions
Penetrating ability of beta particles + Range in air + Ionising strength + Typical energy
Stopped by a few mm of aluminium
~1m
Weak
Continuous spectrum
Penetrating ability of gamma particles + Range in air + Ionising strength + Typical energy
Stopped by about 10cm of lead
~1km
Very weak
Characteristic emissions
What are the direct and indirect effects of ionising radiation on living tissues and cells?
- Direct damage to DNA through breaks and mutations
- Indirect generation of free radicals which initiate harmful chemical reactions within cells and cause similar effects as direct action.
At low levels of exposure, cells have mechanisms that can repair the damage, but with prolonged exposure, severe damage can lead to creation of tumour cells or cell death.
Intensity of light
The amount of energy the light carries per unit time per unit area.
How do the wave model and the photon model explain instantaneous emission of electrons (even for light of low intensity)
Wave:
Very intense light should be needed for immediate effect.
Photon:
A single photon is enough to release one electron.
How do the wave model and the photon model explain threshold frequency below which there is no emission
Wave:
Any frequency can give rise to emission if exposure time is long enough.
Photon:
A low frequency photon has energy less than work function so there is no release of an electron.
How do the wave model and the photon model explain max KE of electrons being independent of intensity
Wave:
Greater intensity means more energy so the electrons should have more energy
Photon:
Greater intensity does not mean more energetic photons, so electrons cannot have more energy
How do the wave model and the photon model explain max KE being dependent on frequency
Wave:
Increasing intensity and not frequency increases the energy of electrons
Photon:
Higher frequency means more energetic photons so electrons gain more energy
How do the wave model and the photon model explain the rate of emission of electrons being dependent on intensity
Wave:
Greater intensity so more energy, so more electrons emitted.
Photon:
Greater intensity means more photons per second, so more electrons are emitted per second.
Explain the existence of the continuous background spectrum
1) EM radiation is produced whenever a charged particle is decelerated or accelerated
2) The electrons hitting the metal target have a distribution of decelerations so a continuous spectrum is produced.
How are Eddy currents produced
If the conductor is a solid plate, the rate of cutting is not the same over the whole plate, so different emf are induced in different parts of the plate. => eddy currents flow simultaneously along many different paths in swirls
This causes heat energy to be dissipated from the plate as Eddy currents flow in the conductor
Ohmic resistor
As potential difference V increases, current I increases proportionately. Thus resistance R remains constant.
Filament lamp
As potential difference V increases, current I increases initially. Further increase of V causes a less than proportionate increase in I, so R increases with increasing V.
This is because for a metal, as temperature increases, the number density of free charge carriers, n, will not increase significantly but the amplitude of atomic vibration increases. So R increases
Semiconductor diode
As V increases, temperature of the semiconductor increases. Electrons in semiconductor are more likely to have sufficient energy to escape from a particular atom if the temperature is higher, which increases n significantly. At the same time, there is also an increase in rate of interaction of electrons with the vibrating atoms. However, as the increase in n predominates over the rate of interactions of electrons with the lattice, the overall effect is that R decreases.
In the reverse-biased region, there is no current flow through the diode until the breakdown voltage.
NTC Thermistor
An NEGATIVE TC thermistor’s resistance falls as the temperature rises. As the temperature increases, the number of charge carriers per unit volume in the material increases, reducing its resistance. As such, its I-V characteristic is the same as that for a semiconductor diode for positive values of V and I.
Isothermal process
The temperature of the system remains constant. => Constant internal energy of an ideal gas (pV is constant)
Isobaric process
The pressure of the system remains constant => temperature changes (because it is on a different isotherm) and volume changes
Isochoric/Isovolumetric process
The volume of the system remains constant => (different isotherm means) temperature changes, pressure also changes
Adiabatic process
There is no heat exchange between the system and the environment, that is, no heat supplied to or removed from the system.
(In an adiabatic expansion, since no heat is supplied to the system for it to do work, it USES ITS INTERNAL ENERGY, thus temperature decreases. Pressure also decreases.)
The path for adiabatic changes are steeper than isotherms as pressure changes more rapidly than volume.
How to obtain pV = 1/3Nm<c^2>
- Define parameters: A cubical box of sides l, containing N molecules of gas
- Change in momentum of molecule = change in momentum of wall so its twice
- Time travelled before further collision = distance/ speed
- Use N2L and N3L to obtain rate of change of momentum of wall due to one molecule
- Add up all the rates of change of momentum
- Pressure = Force/Area by considering volume shift to other side of eqn
- Convert to 3D
