# Physics MCQ's 3 Flashcards

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

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

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

95%

How is the standard error of the mean calculated?

The standard error of the mean (SEM)

= standard deviation / square root of the sample size.

How do you calculate 95% confidence interval?

sample mean +/- (1.96 x SEM)

In a process changing exponentially:

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

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

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

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

How does air humidity affect the risk of sparks?

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.

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

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.

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

Incorportate resistance, this reduces current flow.

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

Prevents current flow through the patient.

Soda lime: T/F

- can regenerate when left unused?
- turns white when ‘exhausted’

- 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.
- F - The colour change with soda lime varies with the specific make of soda lime used, and depends on the dye indicator.

Soda lime: T/F

- absorbs CO2 better when dry?
- reacts with CO2 to produce sodium bicarbonate?

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

What ingredients are used in soda lime?

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

How is temperature compensated with a vaporiser?

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.

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

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.