Physics MCQ's 3

Question 1

What percentage of values lies within 1 standard deviation of the mean in a normal distribution?

Answer 1

68% within one standard deviation, and 16% above and below SD.

Question 2

What percentage of values lies within 2 SD’s of the mean?

Answer 2

95%

Question 3

How is the standard error of the mean calculated?

Answer 3

The standard error of the mean (SEM)

= standard deviation / square root of the sample size.

Question 4

How do you calculate 95% confidence interval?

Answer 4

sample mean +/- (1.96 x SEM)

Question 5

In a process changing exponentially:

1. What is the time constant?
2. One half life is ____ of a time constant.
3. The rate of change is by constant proportions? T/F

Answer 5

1. time taken for 63% of the process to occur (1/e)
2. 0.693 (one third)
3. True (time constant)

Question 6

Electrical safety: how many cores does Class 1 equipment have?

Answer 6

Must have a live, neutral and earthed wire as standard safety precaution.

Question 7

How does air humidity affect the risk of sparks?

Answer 7

a relative humidity above 50% reduces the risk of sparks from accumulated static electricity charge; dry air allows sparking over a greater distance than air containing water vapour.

Question 8

What is incorporated into the leads of diathermy plate for electrical safety.

Answer 8

A capacitor is used to protect patient from electrical shock from mains electricity.

The isolating capacitor has low impedance to a high-frequency current, i.e. diathermy current.

The capacitor has a high impedance to 50-Hz current thus protecting the patient against electrical shock.

Question 9

How can you reduce the risk of harmful current leak in ECG leads?

Answer 9

Incorportate resistance, this reduces current flow.

Question 10

How does using a single earthing point for electrical equipment protect the patient?

Answer 10

Prevents current flow through the patient.

Question 11

Soda lime: T/F

1. can regenerate when left unused?
2. turns white when ‘exhausted’

Answer 11

1. T - When left unusued, the carbonate on the surface of the granules will move to the inside of the granule and hydroxide to the outside.
2. F - The colour change with soda lime varies with the specific make of soda lime used, and depends on the dye indicator.

Question 12

Soda lime: T/F

1. absorbs CO2 better when dry?
2. reacts with CO2 to produce sodium bicarbonate?

Answer 12

1. F - The initial chemical reaction is between water and carbon dioxide to form carbonic acid, so water increases the absorption.
2. F. - Carbonic acid formed from water and carbon dioxide reacts with sodium hydroxide to form sodium carbonate (NOT BIcarbonate)

Question 13

What ingredients are used in soda lime?

Answer 13

calcium hydroxide, sodium hydroxide and potassium hydroxide - typical for that used in the UK.

Question 14

How is temperature compensated with a vaporiser?

Answer 14

Major method - varying the splitting ratio using and bimetallic strip. As temperature decreases, the strip bends, allowing more fresh gas flow to enter the vaporizing chamber

The actual specific heat capacity of the metals is low, so although there is a large lump of metal incorporated - the contribution of this to the temperature is small.

Question 15

Temperature compensation within a vaporiser can be avoided by adding liquid anaesthetic directly to the gas stream? T/F

Answer 15

T - This method allows a fixed volume of liquid to be released per unit time, all of which is vaporised. No contact between the liquid reservoir and the gas occurs; therefore, no temperature compensation is needed.

Question 16

An Ayres T-piece with a Jackson-Rees modification has an advantage over a circle system for paediatric anaesthesia because: T/F

a. higher gas flows can be utilised
b. pure oxygen can be administered more easily
c. there is less danger of a pneumothorax with controlled ventilation
d. resistance to breathing is lower during spontaneous ventilation
e. PaCO2 will not decrease as much during controlled ventilation

Answer 16

a. F - Higher flows are needed - but this is not an advantage.
b. F - It does take longer for 100% pure oxygen to be available in a circle system compared with the T-piece. However, this is not a significant disadvantage.
c. F - All forms of controlled ventilation carry the risk of pneumothorax.
d. T - Unlike the circle system, the modified T-piece has no valves, giving it a significantly lower resistance to gas flow during spontaneous respiration.
e. F - PaCO2 depends on the settings used during controlled ventilation, not on the system in use.

Question 17

In a time cycled ventilator providing a constant pressure during the inspiratory phase:

A. the source of driving gas at 4 bar is required? T/F

B. the peak inspiratory pressure in an indication of airways resistance

Answer 17

A. F - The pressure of driving gas can be any value above the likely peak pressure to be developed.

B. F - In a constant pressure generator, inspiratory pressure is determined by the machine setting, not the patient’s lungs.

Question 18

True or False:

an alternating (50 Hz) current of 100 mA passing between L and R hands at a potential difference of 240 V is safe?

Answer 18

False.

A current of 100 mA would be enough to cause ventricular fibrillation.

Question 19

True or False:

a current of 100 mA passing between L hand and heart at a potential difference of 2 V is safe?

Answer 19

False.

The current flow, not the voltage, is the key factor in causing patient injury.

Question 20

True or False:

operating theatre floors have a very low electrical resistance to prevent static charge building up

Answer 20

Operating theatre floors no longer have very low electrical resistance to prevent static build-up.

Question 21

In a vaporiser is the specific heat capacity of metals high or low?

Answer 21

The actual specific heat capacity of metals is relatively low, so although there is a large lump of metal incorporated, the contribution of this to temperature compensation is small.

Question 22

When does a liquid boil with reference to SVP?

Answer 22

When SVP equals ambient pressure.

Question 23

A liquid boils at a higher/lower temperature if ambient pressure is reduced?

Answer 23

LOWER temperature - If the pressure is reduced, then the saturated vapour pressure required to equal ambient pressure is reduced and the liquid boils at a lower temperature.

Question 24

Does a liquid boil above or below its critical temperature?

Answer 24

BELOW:

Critical temperature is the temperature above which a substance cannot be liquefied, no matter how much pressure is applied.

So a substance exists only as a gas above its critical temperature.

Question 25

The non-interchangeability of Schrader probes depends upon what?

Answer 25

This is the principle of the Schrader system - each specific gas probe has a PARTICULAR COLLAR SIZE to open the matching valve on the Schrader outlet.

Once the pipeline probe is disconnected, the valve closes.