Physics Flashcards
Laminar flow
The situation when any fluid (gas or liquid) passes smoothly and steadily along a given path, as described by the Hagen Poiseuille equation
Viscosity is the important property for laminar flow
Turbulent flow
When a fluid flows unpredictably with multiple eddy currents, and is not parallel to the sides of the tube through which it flows
Density is the important property for turbulent flow
Reynold’s Number
A dimensionless number which describes the likelihood of fluid flow being either turbulent laminar.
<2000 likely to be laminar
>2000 likely to be turbulent
Re = pvd/n
P is densitv
V is velocity
D is diameter of tube
N is viscosity
Hagen-Poiseuille equation
Flow = pi p r4 / 8 nl
P is pressure drop
R is radius
N is viscosity
L is length
Flow is proportional to the 4th power of the radius so if r doubles then flow increases x 16
Bernoulli Principle
An increase in flow velocity of an ideal fluid will be accompanied by a decrease in pressure in order to conserve energy
Venturi Effect
The introduction of a constriction to fluid flow within a tube causes velocity to increase and therefore pressure to fall
Surgical diathermy
Works on the principle of current density, that a current applied over a small area has high density and heating will occur
Ultrasound
Sound waves with a frequency >20KHz
Medical ultrasound uses waves in the 2-15MHz spectrum
Increasing frequency gives greater resolution but reduces penetrating capacity
Piezoelectric effect
Phenomenon by which a mechanical stress applies to crystalline substances produces a potential difference
Resolution
Ability to distinguish to objects as separate
Can be spatial or contrast (those with similar echo reflective properties)
Absolute Humidity
The total mass of water vapour present in the air per unit volume (AH, kg.m-3 or g.m-3 )
Relative Humidity
The ratio of the vapour pressure of water in the air compared with the saturated vapour pressure of water at that temperature (RH, measured as a %).
Dew Point
The temperature at which the relative humidity of the air exceeds 100% and water condense out of the vapour phase to form a liquid.
Humidity
The amount of water vapour present in the atmosphere and is subdivided into two types: absolute and relative
Latent Heat
The heat required or released when a substance changes state
Heat Capacity
The heat energy required to raise the temperature of a given object by one degree
Specific Heat Capacity
c = ΔQ/mΔT
the amount of heat energy required to raise the temperature of a mass of 1kg by 1 Kelvin.
c = ΔQ/mΔT
where…
• c = the specific heat capacity of the substance
• ΔQ = the amount of heat energy required in kilojoules (kJ)
• m = the mass of the substance being heated in kilograms (kg)
• ΔT = the change in temperature in Kelvin (K)
The Triple Point of Water
The temperature at which all three phases of water are in equilibrium at 611.73Pa. It occurs at 0.01oC.
Force
Force is that influence which tends to change the state of motion of an object, measured in Newtons
F = ma m=mass and a=acceleration
Newton
1 Newton is that force which will give a mass of 1Kg an acceleration of 1m/s/s
N = Kg.m.s-2
Pressure
Pressure is force applied over a unit area, measured in pascals
P=F/A
Pascal
1 Pascal is equal to a force of one newton applied over an area of one square metre (N.m-2)
Energy
Energy is the capacity to do work, measured in joules. (mechanical, chemical, electrical or thermal/heat)
Work
Work is the result of a force acting upon an object to cause its displacement in the direction of force applied
J=FD where F is force and D is distanced travelled.
Joule
1 Joule is the work done when a force of one newton moves one metre in the direction of the force.
Power
Power is the rate at which work is done, measured in watts
W=J/s where J is work done and s is time in seconds
Watt
1 Watt is the power expended when one joule of energy is consumed in one second.
Critical Temperature
The temperature above which a gas cannot be liquified regardless of how much pressure is applied
Critical Pressure
The pressure needed to liquify a gas at its critical temperature
Boyle’s Law
At a constant temperature, the volume of a fixed amount of a perfect gas varies inversely with its pressure
Charles’ Law
At a constant pressure, the volume of a fixed amount of a perfect gas varies in proportion to its absolute temperature
Gay-Lussac’s Law
At a constant volume, the pressure of a fixed amount of a perfect gas varies in proportion to its absolute temperature
Gas vs Vapour
A gas is above its critical temperature
A vapour is a substance in the gaseous phase below its critical temperature - and can be liquified with increased pressure
Henry’s Law
The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid
Dalton’s Law
In a mixture of gases, the pressure each gas exerts is the same as if it existed alone in the same volume
Avogadro’s constant
Equal molar volumes of all gases under standard temperature and pressure occupy the same volume
A mole
6.02x10^23
The quantity of a substance that contains the same number of molecules as there are atoms as there are in 0.12g of Carbon 12
Viscosity
A liquid’s resistance to flow (Pascal-seconds)
Density
Mass of a substance per unit volume (g/mL)
Osmole
The number of particles equal to Avogadro’s number - 6.02 x 10^23
Osmolarity
The number of osmotically active particles per LITRE of SOLUTION
(mmols/L)
Osmolality
The number of osmotically active particles per KILOGRAM of SOLVENT
(mmols/Kg)
Osmotic Pressure
The pressure exerted within a sealed system of solution in response to the presence of osmotically active particles on one side of a semi-permeable membrane
(kPa)
Colligative Properties
Those properties of a solution that vary according to osmolarity:
Depression of freezing point
Reduction of vapour pressure
Elevation of boiling point
Increase in osmotic pressure
Raoult’s law
Depressing of freezing point/reduction in vapour pressure of a solvent is proportional to the molar concentration of the solute
Surface tension
The IMF developed at the surface of a liquid that tends to resist the action of external forces (N.m-1)
LaPlace’s Law
(sphere)
T=Pr/2 (T is wall tension, P is pressure, r is radius)
A given wall tension, a sphere of smaller radius will have greater pressure, hence why a balloon is difficult to inflate at first/small alveoli collapse without surfactant
Resistance
Opposition to flow of direct current (ohms)
Reactance
Opposition to flow of alternating current (ohms)
Impedance
Total of the resistive and reactive components of opposition
Ohm’s Law
At a constant temperature
V=IR
V is voltage, I is current and R is resistance
Capacitor
A device that stores electrical charge
Capacitance
The ability of a capacitor to store charge (farads, F)
Farad
A capacitor with a capacitance of one farad will store one coulomb of charge when one volt is applied
F= C/V
Inductor
An electrical component that oppose changes in current flow by the generation of an electromotive force
Inductance
The measure of the ability to generate EMF under the influence of changing current (henry, H)
Henry
One henry is the inductance when one ampere flowing in the coil generates a magnetic field strength of one weber
H=Wb/A
Wheatstone Bridge
An electrical circuit designed to measure an unknown resistance, by balancing two limbs of a bridge circuit so the voltage between the limbs is zero
R2/R1 = Rx/R3
Resonance
The condition in which an object or system is subjected to an oscillating force having a frequency close to its own natural frequency
Natural Frequency
The frequency of oscillation that an object or system will adopt freely when set in motion or supplied with energy (hertz, H)
Damping
A decrease in the amplitude of an oscillation as a result of energy loss from a system owing to frictional or other resistive forces
A measuring system attempting to respond to an instantaneous change in the measured value - e.g. when you suddenly stop flushing the arterial line
Semi-conductor
Materials with conductivity between conductors and insulators.
Reasonably well bound outer shell electrons but with additional energy, the electrons are able to move and allow current to flow.
Cleaning
The process of physically removing foreign material from an object without necessarily destroying any infective material.
Disinfection
The process of rendering an object free from all pathogenic organisms, EXCEPT bacterial spores.
Sterilisation
The process of rendering an object free from all pathogenic organisms, INC bacterial spores.
Decontamination
A combination of cleaning, plus disinfection or sterilisation.
Under-damped
Output value oscillates around the baseline for some time
Coefficient = 0-0.3
Over-damped
Overly blunted, inaccurate
Coefficient > 1
Zero Damping
Theoretical situation (vacuum)
Coefficient = 0
Amplitude of oscillations does not diminish with time
Critical Damping
No overshoot, so very accurate but too slow
Coefficient = 1
Optimal Damping
Rapid response with minimal overshoot
0.64
Diode
Allows current flow in one direction only
Transformer
Increases or decreases the voltage in an AC circuit
