Physics

Question 1

Thermocouples

Answer 1

A pair of bimetallic strips which create a small voltage at their junction proportional to temperature (Seebeck effect)

Question 2

CVC

Answer 2

14G = 1.63mm diameter
16G = 1.3mm diameter
Transducer placed at 4th ICS, mid-axillary line

Question 3

Critical pressure

Answer 3

Is the pressure required to liquefy a substance at its critical temperature

Question 4

Dalton’s law

Answer 4

The pressure exerted by a gas in a minute of gases is the same as it would be if that gas alone were present
The pressure of a mixture of gases is the sum of the individual partial pressures

Question 5

Henry’s law

Answer 5

The amount of gas dissolved in a liquid is proportional to the partial pressure of the gas

Question 6

Density of volatiles

Answer 6

Sevo 6.12
Halothane 6.48
Desflurane 5.44
Isoflurane 5.19
Oxygen 1.23
N2 1.02
Air 1.22
CO2 1.98
Helium 0.17

Question 7

Pressure units

Answer 7

1kPa = 0.01 atm = 1000Nm2 = 10.2cmH2O = 7.5mmHg

Question 8

Mercury

Answer 8

Manometer measures gauge pressure so has the top open to atmospheric pressure
Barometer measures atmospheric pressure so the top is sealed and creates a torricelian vacuum
Absolute pressure = gauge pressure + atmospheric pressure

Question 9

Newton

Answer 9

Force required to move 1kg 1metre per second per second

SI units: kg.m.s^-2

Question 10

Pascal

Answer 10

Force of 1 newton over 1 m2
Kg.m.s^-2 / m2
= kg.m^-1.s^-2

Question 11

Joule

Answer 11

Measures energy/work done when a force of 1N moves an object by 1m in the direction of its motion
= Force x distance
= Kg.m.s^-2 x m
= kg.m2.s^-2

Question 12

Power

Answer 12

Rate of energy transfer, measured in Watts
Joules / time
Kg.m^2.s^-2 / s
=kg.m^2.s^-3

Question 13

Volts

Answer 13

Units of electrical potential difference
Potential difference when a current of 1A dissipates 1W of power
1W/1A
Kg.m2.s^-3 / A
Kg.m2.s^-2.A^-1

Question 14

Micro shock

Answer 14

Right ventricle is more sensitive than left

Current cannot induce asystole

Question 15

electric shock

Answer 15

Frequency should be >100KHz to avoid arrhythmias

Extensor muscles are affected more

Question 16

Electricity supply to theatre

Answer 16

Single phase supply 
3 wires - line, neutral and earth 
240V
Local earth connection (not substation)
Mains frequency is 50Hz

Question 17

Electrostatic interference

Answer 17

Can be reduced by screening the cables with a conductive barrier (not insulating)
A form of capacitative leakage so increased at higher frequencies
Doubling the separation halves the field strength between the 2 wires

Question 18

Electromagnetic interference

Answer 18

Requires the lead to be drawing a current (need AC to induce a magnetic field)
Cannot be prevented by screening
Magnetic field strength is inversely proportional to distance^2

Question 19

Requirements of an earth connection

Answer 19

Resistance <0.1ohm
Leakage current <0.5mA for Type 1
Local earth connection not connected to the substation
Must be able to carry 25A for 5s (earth surge test) - this must not require a voltage of more than 2.5V if R <0.1ohm

Question 20

the star point

Answer 20

Connects one side of the 240V supply to the earth at the substation, creating the neutral wire
Protects from lightning strike
Not used in a three phase electricity supply

Question 21

Electrical transformer

Answer 21

Efficiency is 95%

Question 22

Electrical burns

Answer 22

Depend on size of current passed (and therefore voltage and resistance)
Depend on current density
Usually focussed at areas of high current density - entry and exit points

Question 23

Scavenging

Answer 23

Tubing should be low resistance and low compliance to prevent collapse under negative pressure
Float controls protect the system
Should be able to generate flows of >25L/min
Should be able to generate pressure of -500mmHg is 10s

Question 24

Soda lime

Answer 24

Can produce CO with desflurane, halothane and isoflurane

1kg can absorb 250L CO2

Question 25

T-piece

Answer 25

FGF must be delivered at the patient end, therefore Mapleson D, E and F can all function as T-pieces

Question 26

Mains voltage

Answer 26

Root mean square = 240V = the constant value which would result in the same power output as the alternating voltage
Peak value of alternating voltage is 339V

Question 27

Diathermy

Answer 27

Uses frequencies of 1-5MHz
High current density at the active electrode and low current density at the pad
Coagulation mode uses short bursts of sine waves, cutting mode uses continuous sine waves
AC not DC is used

Question 28

Isolation transformers

Answer 28

Create an unearthed circuit with the patient

Question 29

Inductors

Answer 29

Electrical impedance is directly proportional to frequency
Z = 2 x Pi x f x L
Where L = inductance
Voltage is proportional to rate of change of current so more voltage in AC which slows the current down more, so inductors filter high frequency currents (“low pass filter”)
Frequency-dependent resistance is called reactance

Question 30

Capacitors

Answer 30

Electrical impedance is inversely proportional to frequency
Z = 1/2 x Pi x f x C
Where C = capacitance
Current flow is proportional to the rate of change of voltage in AC
Current flow is negatively exponential in DC
In a capacitor, more current flows at a higher frequency
RC circuit is a mathematical integrator - low pass filter
CR circuit is a mathematical integrator - high pass filter

Question 31

Bain Circuit (Mapleson D)

Answer 31

FGF in inner tube

FGF of 3x MV is needed in spont vent pts

Question 32

Henry’s Law

Answer 32

Solubility of a gas in a liquid is proportional to the partial pressure of the gas at the liquid’s surface

Also, solubility of a gas DECREASES as temperature INCREASES