Physics MCQ's 8

Question 1

What is the latent heat of vaporisation?

Answer 1

The amount of energy required to convert 1kg of a liquid at a given temperature to a vapour at the same temperature.

Question 2

What conditions does latent heat if vapourisation vary with?

Answer 2

Varies with ambient temperature.

Question 3

What is the latent heat of vapourisation at critical temperature?

Answer 3

Zero- at critical temperature a substance changes spontaneously from liquid to vapour without any external energy supply.

Question 4

How is the latent heat of vapourisation lost?

Answer 4

Lost to the environment as condensation.

Question 5

What does ‘adiabatic’ mean?

Answer 5

a thermodynamic process: relating to or denoting to a process or condition in which heat does not leave or enter the system.

Question 6

How does rapid gas expansion affect temperature?

Answer 6

Fall in temperature, as kinetic energy from the gas is required to overcome the Van der Waals forces between the molecules.

Question 7

How can convective heat loss in the patient during surgery be minimised?

Answer 7

increasing ambient theatre temperatures, warming blankets, and forced air warm blankets.

Question 8

Infra-red radiation increases or decreases the energy of molecules of gas?

Answer 8

Increases.

Question 9

What is collision broadening?

Answer 9

When different gases molecules in a mixture overlap in wavelength in which they absorb infra-red radiation.

Instead of showing separate peaks, there the gases are centered around one peak.

Question 10

Electromagnetic spectrum: how is the wavelength related to frequency?

Answer 10

velocity = frequency x wavelength.

wavelength = v/f

Velocity is a constant. Therefore wavelength is proportional to the reciprocal of frequency.

Question 11

What is the range of frequency between X-rays and Gamma rays?

Answer 11

10^18Hz and 10^21Hz

Question 12

What is the order of frequency in the electromagnetic spectrum highest to lowest? Wavelength?

Answer 12

1. Gamma waves (highest frequency)
2. x-rays
3. UV
4. Visible light
5. Infrared
6. Radiowaves (lowest frequency)

Opposite order in terms of order of wavelength, as with higher frequency-shorter wavelength

Question 13

What would cause the current density to be too high in electrocautery equipment patient plate?

Answer 13

If the patient plate has a reduced area of contact with the patient, the current density at the plate may be high enough to cause burns.

Question 14

How can faulty grounding of the table cause accidental burns with electrocautery equipment?

Answer 14

• may lead to burns if the patient is in contact with the metal table and the current returns to earth through the table rather than the neutral plate.

Question 15

Entonox: the 50:50 mixture is by weight/volume/percentage?

Answer 15

By volume

Question 16

What form do nitrous oxide and oxygen exist in the cylinder?

What is the pseudo-critical temperature?

Answer 16

At room temperature (15) at 137 bar, gaseous mixture.

But at or below -5.5 degrees, nitrous oxide would settle to the bottom. Risk of inhaling hypoxic mixture if stored upright after pure oxygen is consumed.

-5.5 degrees is the pseudo-critical temperature; separates into its gaseous components.

Question 17

What is the airway pressure at end-expiration?

Answer 17

Zero

Question 18

What is lung compliance?

Answer 18

Change in volume per unit change in distending pressure.

Question 19

Does pre-treatment with Salbutamol affect lung compliance?

Answer 19

Yes, bronchodilatation with salbutamol will reduce airways resistance and increase lung compliance.

Question 20

What is the normal lung compliance for an adult approximately?

Answer 20

200mL.cm H2O-1 in a healthy adult.

Question 21

What equipment can be used to measure lung compliance?

Answer 21

1. Spirometer –> can be used to measure volume changes.
2. Oesophageal balloon –> can be used to measure intrapleural pressure which is necessary to measure distending pressure.

Intrapleural pressure - atmospheric pressure = distending pressure.

The patient takes a very deep breath then exhales in stages, stopping to allow volume and pressure measurements. At these stages there is no air movement and alveolar pressure equals atmospheric pressure.

Question 22

What is the approximate anatomical dead space?

Answer 22

2 ml/kg
body weight
in healthy adult

Question 23

How is physiological dead space calculated?

Answer 23

Physiological dead space

= anatomical dead space + alveolar dead space.

Question 24

What is alveolar dead space?

Answer 24

Alveolar dead space is the volume of gas entering unperfused alveoli in each breath.

Question 25

What method is used to measure physiological dead space?

Answer 25

Bohrs method ; VD/VT = (PaCO2-PeCO2)/PaCO2.

(arterial - expired)/ arterial

Question 26

Method used to measure anatomical dead space?

Answer 26

Anatomical dead space is measured by:

1. the single breath nitrogen washout
   - Fowler’s method.

Question 27

What are the steps in the Fowler method of anatomical dead space measurement?

Answer 27

1. A single breath of 100% oxygen is given to the subject.
2. The oxygen replaces nitrogen in the anatomical dead space.
3. The exhaled breath has its volume and nitrogen concentration measured.
4. The graph of nitrogen concentration over volume can be used to calculate the anatomical dead space.

Question 28

Cyroprobe - what’s the minimum effective temperature they can work at?

Answer 28

• 70 degrees C

Question 29

T/F: Infra-red radiation is not absorbed by glass?

Answer 29

False, it is absorbed by glass.

Question 30

T/F: Entonox cylinders should be stored upright?

Answer 30

False, risks of breathing a hypoxic mixture reduced when stored at or above 5 degrees C.

Question 31

T/F: an oesophageal balloon can be used to measure the static transpulmonary pressure.

Answer 31

True