definitions Flashcards
fundamental units
seven basic units of the SI measurement system: kilogram, second, mole, metre, ampere, Kelvin, candela
accuracy
how close a measurement is to the accepted value (measure of correctness)
precision
agreement among the number of measurements made (how large is the range, measure of exactness)
random error
produced by unknown/unpredictable variations e.g. temperature changes, estimations when reading instruments
can be decreased by increasing no. of trials
systematic error
associated with a particular instrument or experimental technique causing the measured value to be off the same amount each time. e.g. consistently reading the volume wrong
vector
a quantity with both a magnitude and direction
scalar
a quantity with magnitude only
displacement (s)
distance traveled in a particular direction
velocity (u, v)
rate of change of displacement
speed (u,v)
rate of change of distance
acceleration (a)
rate of change of velocity
Newton’s first law of motion
an object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force
Newton’s second law of motion
an unbalanced force will cause an object to accelerate in the direction of the net force. the acceleration of the object is proportional to the net for and inversely proportional to its mass
Newton’s third law of motion
when two bodies A and B interact, the force that A exerts on B is equal and opposite to the force that B exerts on A
translational equilibrium
net force acting on a body is zero
linear momentum (p)
product of mass and velocity
impulse (J)
change in momentum
law of conservation of linear momentum
the total momentum of an isolated system remains constant
work (W)
the product of a force on an object and the displacement of the object in the direction of the force
kinetic energy (Ek)
Ek=1/2 mv^2
principle of conservation of energy
the total energy of an isolated system remains constant OR energy can neither be created nor destroyed but only transformed from one form to another or transferred from one object to another
elastic collision
a collision in which kinetic energy is conserved
inelastic collision
a collision in which kinetic energy is not conserved
power (P)
the rate at which work is done OR the rate at which energy is transferred
efficiency (eff)
the ration of useful energy output to the total energy input
newton’s universal law of gravitation
The force of gravity between two objects is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them and acts along a line joining their centres.
gravitational field strength (g)
gravitational force per unit mass on a point mass
gravitational potential energy (Ep)
the work done in moving a mass from infinity to a point in space
gravitational potential (V)
the work done per unit mass in moving a mass from infinity to a point in space
equipotential surface
every point on it has the same potential
escape speed (Vesc)
minimum speed of a body needs to escape the gravitational attraction of a planet
Kepler’s thrid law
the ratio of the orbital period squared to the average orbital radius cubed is constant for all planets
weightlessness in free-fall
a sensation of weightlessness because a person is falling freely toward the Earth, hence there is no normal reaction force acting on the person due to gravity
weightlessness in orbital motion
a sensation of weightlessness due to the spacecraft and all objects in it being in constant free-fall together as they circle Earth
weightlessness in deep space
a sensation of weightlessness due to the minimal pull of gravity very far from any massive object
temperature
a measure of the average random kinetic energy of the particles of a substance
thermal equilibrium
two objects are in thermal equilibrium when they are at the same temperature so that there is no transfer of thermal energy between them
internal energy of a substance (U)
the total potential energy and random kinetic energy of the molecules of the substance
thermal energy (Heat) (Q)
energy transferred between two substances in thermal contact due to a temperature difference
mole
an amount of substance that contains the same number of atom as 0.012kg of 12C (6.022x10^23)
molar mass
the mass of one mole of a substance
Avogadro’s constant (Na)
the number of atoms in 0.012kg of 12C (6.022 10^23)
thermal capacity (C)
energy required to raise the temperature of a substance by 1K
specific hear capacity (c)
energy required per unit mass to raise the temperature of a substance by 1K
boiling
a phase change of a liquid into a gas that occurs at a fixed temperature
evaporation
when faster moving molecules have enough energy to escape from the surface of a liquid that is at a temperature less than its boiling point, leaving slower moving molecules behind which results in a cooling of the liquid
specific latent heat (L)
energy per unit mass absorbed or released during a phase change
pressure (P)
force per unit area acting on a surface
ideal gas
a gas that follows the ideal gas equation of state (PV=nRT) for all values of P, V, and T (an ideal gas cannot be liquefied)
real gas
a gas that does not follow the ideal gas equation of state (PV=nRT) for all values of P, V, and T
absolute zero of temperature
temperature where the molecules of a substance have stopped moving: Ek=0
Kelvin scale of temperature
an absolute scale of temperature in which 0K is the absolute zero of temperature
Kelvin scale of temperature
an absolute scale of temperature in which 0K is the absolute zero of temperature
first law of thermodynamics (U=∆U+W)
the thermal energy transferred to a system from its surroundings is equal to the work done by the system plus the change in internal energy of the system
Isochoric (Isovolumetric)
a process that occurs at constant volume (∆V=0)
isobaric
a process that occurs at constant pressure (∆P=0)
isothermal
a process that occurs at constant temperature (∆T=0)
adiabatic
a process that occurs without the exchange of thermal energy (Q=0)
entropy
a system property that expresses the degree of disorder in the system
second law of thermodynamics
the overall entropy of the universe is increasing
displacement (for waves)
distance the medium has moved from the equilibrium position in a particular direction (unit: m)
amplitude
maximum displacement of the medium from the equilibrium position (unit: m)
frequency (f)
number of oscillations of the medium (or complete waves passing a point) per second (unit: Hz)
period (T)
time taken for one complete oscillation OR time taken for one cycle to pass a given point (unit: s)
phase difference
difference in phase between two points
simple harmonic motion
takes place when the acceleration of (and the force on) an object is :
- proportional to its displacement from the equilibrium position
- in the opposite direction to the displacement (always directed toward its equilibrium position)
- the gradient = -ω2 (think about a = -ω2x and y = mx, so m = -ω2)
damping
involves a force that is always in the opposite direction to the direction of motion of the oscillating particle
critical damping
when a resistive force is applied to an oscillating system that causes the particle to return to zero displacement in the minimum amount of time
natural frequency of vibration
when a system is displaced from equilibrium and allowed to oscillate freely, it will do so at its natural frequency of vibration
forced oscillations
a system may be forced to oscillate at any given frequency by an outside driving force that is applied to it
resonance
a transfer of energy in which a system is subject to an oscillating force that match es the natural frequency of the system resulting in a large amplitude of vibration
wave-pulse
single oscillation or disturbance in a medium
travelling wave
longitude waves/transverse waves
transverse wave
the particles of the medium vibrate at right angles to the direction of energy transfer
longitudinal wave
the particles of the medium vibrate parallel to the direction of energy transfer
wavefront
a line connecting points on a wave with the same phase/displacement
ray
line drawn to represent the direction a wave is travelling when viewed from above, showing the direction of energy transfer
crest
top of a transverse wave
trough
bottom of a transverse wave
compression
particles are close together in longitudinal wave
rarefaction
particles are spread out in longitudinal wave
wavelength (λ)
shortest distance between two points that are in phase along a wave e.g. crest to crest (unit: m)
wave speed (v)
speed of transfer of the energy of a wave
intensity (I)
power received per unit area (NOTE: for a wave, its intensity is proportional to the square of its amplitude)
law of reflection
The angle of incidence is equal to the angle of reflection when both angles are measured with respect to the normal line
Snell’s law
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency
Refractive Index (Index of Refraction) (n)
the ratio of the speed of the wave in the refracted medium to the speed of the wave in the incident medium
diffraction
bending of a wave around an obstacle
principle of superposition
when two waves meet, the resultant displacement is the vector sum of the displacements of the component waves
constructive interference
superposition of two waves which are in phase with each other
destructive interference
superposition of two waves which are out of phase with each other
path difference
difference in the distances two waves must travel from the sources to a given point
standing (stationary) wave
resultant wave formed when two waves of equal amplitude and frequency travelling in opposite directions in the same medium interfere
- must be same amplitude
- same frequence
- travelling in opposite directions
node
- waves meet out of phase
- destructive interference
- zero amplitude
- path difference = (n+½)λ
antinode
- waves meet in phase
- constructive interference
- maximum amplitude
- path difference = nλ
antinode
fundamental frequency (first harmonic)
lowest frequency mode of vibration of a standing wave
Doppler effect
the change of frequency of a wave due to the movement of the source or the observer relative to the medium of wave transmission
resolution
ability to distinguish between two sources of light
Rayleigh criterion
when the central maximum of one diffraction pattern overlaps the first minimum of a second diffraction patter, the two sources are “just resolved”
polarised light
light in which the electric field vector is oscillating in one plane only
Brewster’s law
when light reflects off a surface it will be polarised in the plane of the surface
eg. reflected off a horizontal surface, will be polarised horizontally
polariser
device that produced plane polarised light from an unpolarised beam
analyser
polariser used to detect polarised light
malus’ law
the transmitted intensity of polarized light is equal to the product of the incident intensity times the square of the cosine of the angle between the direction of the analyzer and the direction of the electric field vibration of the polarized light (I = Io cos2 θ )
optically active substance
one that rotates the plane of polarisation of light that passes through it
law of conservation of charge
the total electric charge of an isolated system remains constant
conductor
material through with electric charge flows freely
insulator
material through which electric charge does not flow freely
coulomb’s law
The electric force between two point charges is directly proportional to the product of the two charges and inversely proportional to square of the distance between them, and directed along the line joining the two charges. (F = k q1 q2 / r2)
electric field strength (E)
electric force per positive unit test charge (E = F/q)
radial field
field that extends radially (like the electric field around a point charge or the gravitational field around a planet)
electric potential (V)
work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. (V = W/q) (V = kq/r) (NOTE: the work done is path independent)
electric potential energy (Ep)
energy that a charge has due to its position in an electric field
electric potential difference (ΔV)
electric potential energy difference per unit charge between two points in an electric field (ΔV = ΔEe / q OR ΔV = W / q)
electron volt (eV)
energy gained by an electron moving through an electric potential difference of one volt
(1 eV = 1.60 x 10-19 J)
electric current (I)
current is defined in terms of the force per unit length between parallel current-carrying conductors (NOTE: one ampere of current is the amount of current in each of two infinitely long straight wires one meter apart experiencing a magnetic force per unit length of 2 x 10-7 newtons)
resistance (R)
ratio of potential difference applied to a device to the current through the device
resistor
device with constant resistance (Ohmic device) over a wide range of potential differences
ohm’s law
the current flowing through a device is proportional to the potential difference applied across it providing the temperature is constant
electromotive force (emf/ε)
total energy difference per unit charge around a circuit (total energy per unit charge made available by the chemical reaction in the battery) (ε = ΔEe/q OR ε = W/q)
internal resistance (r)
resistance inside a battery that causes the battery’s terminal potential difference to be less than its emf
ideal ammeter
one with zero internal resistance - must be placed in series
ideal voltmeter
one with infinite resistance - must be place in parallel
potential divider
two resistors placed in series that divide up the battery’s potential difference (R1 / R2 = V1 / V2)
Light-Dependent Resistor (LDR)
sensor whose resistance depends on amount of light shining on its surface – increase in light causes a decrease in resistance
negative temperature coefficient (NTC) thermistor
sensor whose resistance depends on its temperature – increase in temperature causes decrease in resistance
strain gauge
sensor whose output voltage depends on any small extension or compression that occurs which results in a change of length
magnitude of a magnetic field (B)
ratio of magnetic force on a current carrying conductor to the product of the current and length of wire and sine of the angle between the current and the magnetic field (B = FB / Ilsinθ) (OR: ratio of magnetic force on a charged particle to the product of the charge and its velocity and the sine of the angle between the velocity and the magnetic field) (B = FB / qvsinθ)
direction of a magnetic field
the direction that the North pole of a small test compass would point if placed in the field (N to S)
magnetic flux (Φ)
product of the magnetic field strength and a cross-sectional area and the cosine of the angle between the magnetic field and the normal to the area (Φ = B A cosθ)
magnetic flux linkage
product of the magnetic flux through a single coil and the total number of coils (flux linkage = N Φ)
Faraday’s Law
The emf induced by a time changing magnetic field is proportional to the rate of change of the flux linkage. (ε α N ΔΦ/Δt)
Lenz’s law
The direction of an induced emf is such that it produces a magnetic field whose direction opposes the change in magnetic field that produced it. (NOTE: This is the negative sign added to Faraday’s law. ε= - N ΔΦ/Δt)
root mean square (rms) value of an alternating current (or voltage)
the value of the direct current (or voltage) that dissipates power in a resistor at the same rate (NOTE: The rms value is also known as the “rating.”)
photon
a discrete unit or package of light energy
nuclide
a particular type of nucleus with a certain number of protons and neutrons
isotope
nuclei with the same number of protons (Z) but different number of neutrons
nucleon
a proton or neutron
nucleon number (mass number) (A)
number of nucleons (protons and neutrons) in the nucleus
column interaction
electrostatic force of repulsion between the protons in the nucleus
radioactive decay
when an unstable nucleus emits a particle (alpha, beta, gamma) (NOTE: Radioactive decay is both a random and a spontaneous process.) (NOTE: The rate of radioactive decay decreases exponentially with time.)
alpha particle (α)
helium nucleus (2 protons + 2 neutrons)
beta positive particle (β+)
electron
beta negative particle (β-)
positron (anti electron)
gamma radiation (γ)
high energy (high frequency) electromagnetic radiation
Radioactive Half-life (T1/2)
the time taken for ½ the number of radioactive nuclei in sample to decay
artificial (induced) transmutation
when a nucleus is bombarded with a nucleon, an alpha particle or another small nucleus, resulting in a nuclide with a different proton number (a different element).
