Physics MCQ's 2

Question 1

Which of these devices measure gas flow based on the measurement of pressure gradient across resistance?

Wright flowmeter, pneumotachograph, Wrights respirometer, wet spirometer, rotameter?

Answer 1

Only the pneumotachometer- measurement of pressure drops across a resistance is how gas flow is measured.

Wrights peak flowmeter- relies on the variable orifice principle.

Wrights respirometer- measures gas volume

Wet spirometer- measures gas volume

Rotameter- measures gas flow by variable orifice principle.

Question 2

Which content of which gas cylinder when full is liquid at room temperature?

Answer 2

Nitrous oxide- a full cylinder at room temperature because it’s critical temperature is 36.5.

Question 3

Which of the following affect partial pressure of a mixture of gases when a liquid inhalation agent is allowed to come into equilibrium with mixture of gases in a container?

Atmospheric pressure, 
surface area of liquid, 
volume of liquid, 
temperature of the liquid, 
composition of the gas mixture?

Answer 3

Questions regarding what affects saturated vapour pressure (SVP).

Only temperature can affect SVP.

At boiling point, SVP equals atmospheric pressure.

It does not change with volume, surface area as equilibrium has been reached. Atmospheric pressure can affect concentration but not partial pressure.

Question 4

Regarding pressure/ force relationship:

1. For a given force on a syringe, does doubling the diameter of a syringe reduce the pressure by a factor of four?
2. How is gauge pressure calculated?
3. Pressure required to open an expiratory valve at its minimum setting?
4. Pressure of a full oxygen cylinder?

Answer 4

1. Yes, pressure is for per unit area. Area=Pi x radius squared.
   If you double diameter you increase area by 4.
2. Gauge pressure = absolute pressure - atmospheric pressure
3. 50 Pa
4. 138 atmospheres

Question 5

What is critical pressure?

Answer 5

The pressure required to liquiefy gas at its critical temperature.

Question 6

With the Doppler Effect:
What is the doppler effect?

1. What type of waves does this apply to?
2. What changes are reflected in ultrasound?
3. What happens to the frequency if the receiver is moved away from the source?

Answer 6

Change in observed frequency of a signal when the signal source moves relative to the observer; increasing as the source approaches, decreasing as it moves away.

1. Applies to all waves, both sound and electromagnetic radiation.
2. The change in wavelength and frequency are reflected on ultrasound, not velocity.
3. Moving away shifts to a lower frequency.

Question 7

What is the piezo-electric effect?

Answer 7

Is the ability of certain crystals to contract slightly when subjected to a potential difference.

Such a Crystal will vibrate when an alternating current is applied and can be used to create a waveform form use in ultrasound that exploits the Doppler effect.

Question 8

Summarise how MRI works?

Answer 8

The magnetic field of an MRI scanner aligns atoms with an odd number of nucleons (number of protons plus neutrons).

Bursts if radiofrequency energy are then applied, which are taken up by an external radiofrequency coil. This information forms the basis of the resulting image.

Question 9

For an MRI:
How strong a magnetic field is required?
What type of magnet is required?

Answer 9

2 Tesla

A super conducting magnet cooled by liquid helium.

Question 10

How is the freezing point of a solution affected by osmolality?

Answer 10

Raoults Law: the freezing point is reduced in proportion to the molar concentration of the solute.

Question 11

How does osmolality affect water vapour pressure?

Answer 11

The water vapour pressure varies with osmolality.

Water moves from liquid to gas at the liquid/vapour interface. As the number of osmotically active particles increases in the liquid the number of water molecules leaving the liquid decreases.

Question 12

What is the Chi-squared test?

How many treatments can be compared?

In the two by two tables, what is the number of degrees of freedom?

Answer 12

It is a statistical test for association between two variables. Randomisation if the treatments compared is necessary for findings to be valid. Most often used for qualitative, nominal, clinical data grouped according to treatment and response.

More than two can be compared as long as the response measured is the same for all treatments.

It is the (number of rows -1) x (number of columns -1) therefore 1.

Question 13

The spread of individual results about the mean is indicated by:

Variance, 
standard error of the mean, 
value of chi-squared, 
value of students ‘t’, 
standard deviation

Answer 13

Variance and Standard deviation- positive square root of the variance

Question 14

What is the standard error of the mean?

Answer 14

Is used to calculate a confidence interval, a range of values within which you expect the actual population mean to lie.

Question 15

What is the value of the Students ‘t’?

Answer 15

This is a statistic calculated from two samples of data to test whether or not two samples have been drawn from the same population.

Question 16

Does entonox require a single-stage or two-stage valve?

Answer 16

Entonox requires a two-stage valve to allow on-demand delivery only when a negative pressure is developed in the second-stage delivery.

Question 17

What is the higher value of osmolality urine can have if concentrated?

Answer 17

Concentrated urine can have an osmolality of up to 1400 mOsm/kg

Question 18

Concerning osmolality:

A urinary osmolality of 700 mOsm/kg corresponds to a specific gravity of 1040. T/F

Answer 18

False.

An osmolality of 700 corresponds with a specific gravity of 1020, not 1040.