Physics

Question 1

The SI units ?

Answer 1

1. Seconds: Time
2. Meter: Distance
3. Mole: Amount of substance
4. Ampere: Current
5. Candela: Luminous intensity
6. Kilo: Mass
7. Kelvin: Unit of thermodynamics

Question 2

Derived units ?

Answer 2

1. Force: Newton
2. Pressure: Pascal
3. Energy: Joule
4. Power: Watt
5. Frequency: Hertz
6. Volume: Cubic meter and Litre

Question 3

Force?

Answer 3

That which changes the state of rest or motion of an object, a push or pull of an onject.

Question 4

Newtons second law?

Answer 4

F = MxA

Question 5

Force of gravity ?

Answer 5

9.81 ms-2

Thus

1kg = 9.81N (or 1N = 102g)

Cricoid force = 30-40 Newtons or 3-4kg

Question 6

Pressure?

Answer 6

1 Pascal is a pressure of 1N in 1m-2 (102g/m-2)

The surface area is important

Question 7

Pressure equivalents ?

Answer 7

1. 1 Atm = 101325 Pa
2. 1 Atm = 101.325 kPa (100 kPa)
3. 1 Atm = 1 Bar
4. 1 Atm = 760 mmHg
5. 1 Atm = 760 Torr
6. 1 Atm = 1020 cmH2O
7. 1 Atm = 14.5 lb/inch-2 (PSI)
8. 1 Torr = 1 mmHg
9. 1 kPa = 7.5 mmHg

Question 8

Absolute pressure ?

Answer 8

Absolute = Guage (137) + Atmospheric pressure (1)

Guage pressure = 137 bar
Absolute pressure = 138 bar

Arterial pressure = guage pressure.

E.g; A-line transducer or BP measurement

Question 9

Flow ?

Answer 9

1. Laminar

2. Turbulent

Question 10

Laminar flow?

Answer 10

1. x2 faster at the centre
2. No flow near edges
3. Low velocity
4. Represented by the Hagen-poiseuille equation
5. Re = < 2000

Question 11

Hagen-poiseuille equation?

Answer 11

Q = Ppi r-4/8nl

P = Pressure change

Pi = pi

r-4 = Radius

n = Viscosity

l = Length

Question 12

Turbulent flow?

Answer 12

1. Constriction resulting in increased velocity
2. Higher resistance
3. Re = > 2000

Question 13

Reynolds > 4000 ?

Answer 13

1. Increased velocity
2. Increased characteristic dimension
3. Increased density
4. . Decreased viscosity

Question 14

Reynolds? Turbulent flow

Answer 14

If viscosity is increased then turbulent flow becomes laminar.

p = Density V = Velocity D = Diameter u = Viscosity

p.v.D/u

Question 15

Helium in bronchospasm?

Answer 15

Helium increases viscosity thus making flow laminar

Question 16

Tension?

Answer 16

1. LaPlace law
2. Cylinders = P=T/r
3. Spheres = P=2T/r

Question 17

Tension?

Answer 17

1. As diamter becomes smaller, collapsing pressure becomes greater
2. Without surfactant the small alveoli collapse and empty into the bigger ones

Question 18

Bernoulli principle?

Answer 18

1. Fluid velocity increases as it passes through a constriction and its static pressure must decrease (conservation of energy)
2. Fluid pressure is inversely proportional to its velocity

Question 19

Venturi effect - Extension of the bernoulli principle?

Answer 19

1. Constrictiion, increased velocity and decreased pressure

2. Used in nebulizer masks and atomizers

Question 20

Coanda effect ?

Answer 20

1. Tendency of a fluid to be attracted to a nearby surface

2. This is why ETT has murphy eye

Question 21

Boyles law?

Answer 21

For a given mass at a constant temperature, the pressure times volume is constant

Question 22

Application of Boyle’s law? Calculation of cylinder content

Answer 22

P1.V1 = P2.V2

P1 = Guage pressure of cylinder

V1 = Physical volume of cylinder

P2 = Atmospheric pressure

V2 = Actual amount of gas in cylinder

137 bar x 3L = 1 x V2 = 411L

Question 23

Cylinder content ?

Answer 23

1. CO2 & N2O are liquified under pressure and content by weight
2. Air, O2, He, Heliox, Entonox - Pressure is proportional to volume. Content measured by guage pressure

Question 24

Charles law?

Answer 24

For a given mass at constant pressure the volume is directly proportional to the temperaure.

Question 25

Charles law - Application?

Answer 25

V1/T1 = V2/T2 or V1.T2 =V2.T1 Gases expand when heated and become less dense --> Convection

Question 26

Gay-Lussac's law ?

Answer 26

At constant volume, the absolute pressure of a mass of gas varies directly with the absolute temperature.

Question 27

Gay-Lussac's law - Clinical application?

Answer 27

P1/T1 = P2/T2 or P1.T2 = P2.T1

Question 28

Filling ratio? - Clinical application of Gay-Lussac's law

Answer 28

This is the weight of fluid in the cylinder divided by the weight of water required to fill the cylinder. Cold countries 0.75 Tropics 0.67

Question 29

Universal gas law ?

Answer 29

PV = nRT n = number of moles

Question 30

S.T.P?

Answer 30

Standard temperature = 0 degrees or 273 K Standard pressure = 1 Atm

Question 31

Avogadro's Hypothesis?

Answer 31

Equal volumes of gases at the same temperature and pressure contain equal number of molecules Mole: Is the quantity of a substance containing the same number of particles as there are atoms in 0.012kg fof carbon ( 6.022 x 10-23) One mole of any gas at STP occupies 22.4L

Question 32

Dalton's law of partial pressure?

Answer 32

The total pressure of a mixture of gases equals the sum of the partial pressure of the individual gases

Question 33

Critical temperature?

Answer 33

Temperature above which a substance cannot be liquified no matter how much pressure is applied Above critical temperature the sunstance can only exist as a gas. Below critical temperature, the substance can be a vapor or liquid Oxygen = -119 CO2= 31 N2O = 36.5

Question 34

Critical pressure?

Answer 34

The pressure needed to liquify a gas at its critical temperature. Oxygen = 50 bar / CO2 = 73 bar / N2O = 72 bar

Question 35

Critical volume?

Answer 35

The volume occupied by 1 mole of gas at critical temperature and pressure

Question 36

Tripple point of water?

Answer 36

The temperature and pressure in which water can co-exist in equilibrium in 3 phases . 0.01 degrees and 0.006 Atm

Question 37

Solubility and Henry's law?

Answer 37

At constant temperature, the amount of a given gas that dissolves in a volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. More molecules are soluble at higher pressures. Solubility decreases at higher temperatures.

Question 38

Application of Henry's law ?

Answer 38

Divers disease - They must descend and ascend slowly to avoid supersaturation or decompression

Question 39

Partition coefficient?

Answer 39

- Ratio of the amount of a substance present in one phase as compared to the other. - Measure of the difference in solubilites between two phases - Tension is used for dissolved gases in solution

Question 40

Blood-Gas partition coefficient ?

Answer 40

- Describes solubilities of inhaled anaesthetics in blood - B/G coefficient is inversely related to the induction rate - Faster onset and off-set the lower the B/G partition coefficient

Question 41

Diffusion ?

Answer 41

- Movement from high concentration to low concentration. Passive process driven by gradient and no energy required.

Question 42

Definition of Fick's law?

Answer 42

Rate of diffusion is equal to the concentration gradient x Surface area x diffusion coefficient divided by membrane thickness. Potassium is 30x more soluble than sodium Proportional to solubility Proportional to concentration gradient Proportional to area Inversely proportional to tissue thickness Inversely proportional to square root of molecular weight

Question 43

Raoult's law?

Answer 43

When a solute is added the chemical potential of a solvent molecule is lowered. There is lowering of the vapor pressure and freezing point There is a raise of osmotic pressure and boiling point

Question 44

Osmometer ?

Answer 44

Measures osmolality of a solution using either reduction in vapor pressure or depression of freezing point.

Question 45

Wheatstone bridge?

Answer 45

An electrical circuit used to measure the unknown resistance. Used to measure - Capacitance, inductance and impedence