MEDI 11002 Study Guide - Final Guide: Sound Energy, Kirchhoff'S Circuit Laws, Mass Number
WEEK 1: SCIENCE AND FUNDAMENTALS
• Accuracy is the number of significant digits, the closeness of the measured value to a standard or known value.
Precision is the smallest order of 10 used in the expression of a number and is independent of accuracy.
• Significant digits: 2.05 (3SD); 300 (1SD); 0.05 (1SD)
• Velocity change due to gravity – the longer the fall, the greater the velocity over time (gravity)
• d α t2
WEEK 2: FORCE AND ENERGY
• Inertia – resistance of an object to a change in motion, dependent on mass and evident in both stationary
and moving objects.
• Law of conservation of energy – energy cannot be created or destroyed, it can only be transformed
• Force – an influence in the form of a push or pull that tends to change the state of motion of an object
(Newtons – N).
o Forces in the same direction can be added, opposite directions subtract
• Mechanical equilibrium – net force is zero. Occurs when an object is stationary (static) or in steady straight
motion (dynamic)
• Friction is an opposite or resistive force applied causing motion. Reduces net force
• Newton’s laws:
1. every object continues in its state of motion (whether stationary or moving) unless acted upon by a
non-zero net force
2. acceleration of an object is directly proportional to the net force acting on it, is in the direction of net
force and is inversely proportional to mass of object (i.e. a α F/m)
3. for every action there is an opposite and equal reaction
• When 2 objects exert forces on each other, there is acceleration of each object relative to the other. Since F is
the same magnitude for both objects, acceleration has magnitude dependent on mass (a = F/m).
• Momentum – inertia of motion or tendency of moving object to resist change in motion. Dependent on mass
and velocity M=mv so ∆M = ∆mv hence Ft =∆mv → impulse – change in momentum from force/time
• Work = Fd (measured in joules – 1 joule x 1 meter)
• Power – quantity of work done/time (measured in watts – 1 watt is
1joule/1 second) Energy – the ability to do work (measured in joules)
• Mechanical energy – energy due to movement (kinetic) or relative
motion (potential)
o Kinetic = ½ mv2 → W= KE where W = Fd and KE = ½ mv2 therefore
resubstituting gives Fd = ½ mv2
o Potential = mgh
WEEK 3: STATES OF MATTER
• Isotopes – same number of protons, different number of neutrons
• Compounds – 2+ atoms bonded chemically, mixtures dont have
chemical bonding
• Volume – dependent on mass, pressure, temperature, state or phase and force
• Density (ρ) – mass(m) per unit volume (V) of a material (ρ = m/V) – measured in kg m-3 – fixed for solids
and liquids
• Pressure = force/area (Pa) = 1 Newton/m2
o Pressure α depth // Pressure α density
o Pressure = gph
• Pascal’s principle - For any incompressible fluid at rest in an enclosed container, a change in pressure is
transmitted equally and undiminished to all points in the fluid Volume flow rate = area x velocity (m3/s)
• Continuity of flow (fluid in = fluid out → A1v1 = A2v2)
• Poiseuille’s law - Volume flow rate VFR is directly proportional to pressure drop ∆P along the path and
inversely proportional to resistance of the path to flow (R)
• Bernoulli’s equation (conservation) PV + ½ mv2 + mgh = constant // P + ½ ρv 2 + ρgh = constant
o when the cross-sectional area of a path narrows, the velocity of flow must increase in order to maintain
volume flow rate entering and leaving the location
o Bernoulli effect: when the cross-sectional area of a path narrows. The velocity of the flow must increase
in order to maintain volume flow rate entering and leaving the location
• Laminar – regular flow with little energy removed
• Turbulent – chaotic flow with increased energy removed due to friction generating heat
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WEEK 4: PRESSURE
• Gas in container ↑ T ↑KE ↑collisions = ↑ F → pressure is proportional to density (dependent on number of
molecules [mass] and size of container [volume])
• Boyles law - P1V1 = P2V2 // pressure is inversely related to volume P α 1/V
• ↑ T ↑ F = ↑ P // P α T // ratio of P to T is constant in fixed volume P1/T1 = P2/T2
• Ideal gas law - P1V1/T1 = P2V2/T2 // T is an absolute temp (in Kelvin)
• Kinetic energy of molecules – rotational, vibrational and collisional // temp relative due to translational
energy
• Internal energy – sum of KE and PE // can be changed due to phase change // energy storage or release
• Specific heat capacity c ΔT = Q/cm // ↑ added energy required to raise T ↑ c
• Thermal expansion // ↑thermal expansion coefficient ↑volume change for a unit temperature rise
• Heat transfer // conduction (S & L) // convection (gases and liquids) // radiation (always – EM) Q/t α AT
• Emissivity – relative ability of a surface to emit radiation // good absorber = good emitter
• Phase of a wave // Defines position of wave at a point in time of its cycle // Compares two waves of same
frequency // In-phase: at the same point of cycle simultaneously // Out of phase: At different points in
their cycles
• Transverse waves – direction of disturbance is perpendicular to direction of propagation
• Longitudinal – disturbance is along the same plane, has compressions and rarefactions
• Wave interference - Occurs when two or more waves
occupy the same space simultaneously // Both waves are
disturbances within same medium // Results in a
displacement that is a vector summation of the
displacements from each disturbance
o Types: Constructive → disturbances in the same
direction – increased amplitude due to sum of 2
waves amps
o Destructive → disturbances in opposite directions –
results in decreased amplitude due to subtraction of
two waves amplitudes
WEEK 5: SOUND
• Sound is a pressure wave through a medium of ↑ particle pressure and ↓ particle pressure
• Mechanical wave – compressed or rarefacted // energy converts to kinetic energy upon collision
• Pressure wave – force/area // work is done // some KE is retains as internal nergy causing heat
• Absorption – transfer of wave energy to medium // ↑ % absorption ↓ % of beam transmitted // depends on make-up
and frequency ↑ with increased frequency
• Frequency – determined by the frequency of vibration of source producing pressure wave – maintained if theres not
motion between sender and receiver
• Speed ( c ) - c = fλ // depends on elastic properties of the material // c solids > c liquids >c gases
• Interface – junction of two mediums // causes 100% of sound to move into new material // Incident sound = echoed
sound + transmitted sound // angle of incidence determines angle of reflection // Irregular surfaces – many angles of
incidences causing scattering of reflected sound in many directions // Smooth surfaces reflect uniformly //
Refraction – bending of wavefronts direction as it changes the medium in which it travels, Occurs when wavefront
does not hit interface at 90o
• Intensity – measure of quantity of sound // ↑ energy ↑ wave amplitude // α amplitude2 // α pressure variation2
// intensity = power/area
• Intensity Level (IL) – logarithmic measure of relative intensity to a baseline level
• Resonance - when frequency of incoming pulsed energy matches natural frequency of an object, objects amplitude of
vibration increases greatly // because energy is easily taken up by the object
• ↑ elasticity ↑ ability of particles to go back to where they were after a deforming force was applied
• Doppler:
o If receiver is moving away from the source – the number of wavefronts reaching the receiver during the time is
reduced hence lower frequency
o If receiver is moving towards the source – more cycles per time is reaching the listener hence higher frequency
o DS frequency ↑ magnitude indicates that the receiver is changing position rapidly // Δf α vr
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o When the sender moves: Increased concentration of concentric rings in the space ahead of the moving source
(shorter wavelength) and decreased concentration of rings (longer wavelength) behind the moving source // If
velocity v is constant for a medium wavelength changes and frequency must change in response i.e. v = fλ
WEEK 6: ELECTROSTATICS
• Ionisation – process of causing an atom or molecule to have an imbalance of
charge due to addition or removal of an electron
• 1 coulomb = magnitude of charge on 6.25 x 1018 electrons // SI unit of charge
o Coulombs Law - relates size of force (F) between two charged objects to
quantity of net charge (q) on each and the distance between them (d)
o F α (q1q2)/d2
• Net charge determines magnitude and direction of net force
• Conductors - Relatively loosely bound valence electrons that drift through
material // easily give up electrons // little opposition or energy
• Insulators – tightly bound valence electrons
• Distribution of surplus charge on objects surface depends on curvature of surface & presence of external elastic forces
acting on the object
o EXTERNAL FORCES // causes charges to redistribute on surface to balance forces
1. Object not in contact with another conducting path - object will maintain no net charge state
2. Object brought near but not touching an uncharged object – uncharged object will experience force from
charged object and redistribution of charge occurs
3. Two objects touch – charge redistributes on two objects, including transferring between objects to balance
forces until both objects have some net charge
• Polarising of charge // separating opposites
• Electric fields - Field strength is proportional to concentration of force // Direction of force line is always direction of
motion
• Electrodynamics - Study of moving charges and their interactions with electric and magnetic fields
• Current = charge/time
• Potential difference provides electrical pressure // rise = energy added to the charges // drop = energy removed
• EMF // electromotive force // potential rise // energy provider // provides net fields to give electrons a flow direction
and energy
• Ohmic resistance – opposition of current in a circuit causing heating in the conductor // ↑ resistance ↑ energy
consumption // affected by material, length and area
• Ohms law ) = V/R
• Ks current law – current in = current out
• Ks voltage law – voltage rise is equal to voltage drop –
conservation of energy
• Power = vI
WEEK 7: ELECTRICAL SAFETY
• Short circuits occur from dislodged components in
internal workings resulting in abnormal conducting
path within device.
o Circuit limiting device (CLD ) – current sensitive
switch in the circuit to open the circuit loop if maximum allowable current is exceeded e.g. fuse, circuit breaker
o Residual current device (RCD) – circuit monitoring device that works on principle that a normal circuit operation
has equal current magnitude in active and neutral wires
• DC voltage – steady voltage applied in one direction
• AC voltage – voltage alternates in a sine wave pattern
• 3 prong (class 1)
o Active/live wire carry charge flow to the component
o Neutral/return wire carry charge from component
o Ground/earthing wire o normally inactive
▪ connects metal casing of device to earth/ground
▪ provide low resistance pathway
• 2 prong (class 2)
o 2 wires –active and neutral // No ground wire
o Double insulated construction (DIC)
▪ Layer of insulation between inner electrical components and the casing
▪ Safety or shock minimisation
• To receive an electric shock requires current flow,
which requires a PD between body parts
• Double insulation provides safety, shock is unlikely
if both layers are intact
• When hands are wet, then you are the path of least
resistance.
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Document Summary
Week 1: science and fundamentals: accuracy is the number of significant digits, the closeness of the measured value to a standard or known value. and moving objects. Week 2: force and energy: significant digits: 2. 05 (3sd); 300 (1sd); 0. 05 (1sd) Occurs when an object is stationary (static) or in steady straight: forces in the same direction can be added, opposite directions subtract, friction is an opposite or resistive force applied causing motion. Week 3: states of matter the same magnitude for both objects, acceleration has magnitude dependent on mass (a = f/m): when 2 objects exert forces on each other, there is acceleration of each object relative to the other. Since f is motion (potential: kinetic = mv2 w= ke where w = fd and ke = mv2 therefore, momentum inertia of motion or tendency of moving object to resist change in motion.
