Physics MCQ 5 Flashcards
Electrical power is measured in what unit? And how?
Measured in watts
Product of current and voltage
A coil of wire exhibits resistance/ reactance to:
- AC
- DC
What is this vector sum called
- Resistance to DC
- Reactance to AC
Vector sum is called impedance
What is UK mains current?
50 Hz
What is the peak mains voltage in the UK?
340V but quoted as 240V.
Electronic amplifiers usually: T/F
1. Increase signal produced by transducer
- Require protection from defibrillation
- Increase magnitude of random noise as well
- Change one form of energy to another
- Are unaffected by current surges
- T
- T - work with small input currents and need protection from surges.
- T
- F
- F
What current could cause tingling if hand vs burns?
A 50Hz current as low as 1mA causes tingling.
At 100mA this can cause burns as well as VF.
Why is wet skin more prone to burning than dry?
It has a lower impedance.
At what current is VF most likely?
50Hz - mains electricity. Lower or higher VF less likely.
What type of equipment can be used in the body to guard against microshock?
Only type CF equipment.
How can mains interference on an ECG recording by reduced?
- screening leads
- differential input analysers
- common mode rejection ratio
What is the current used in diathermy?
1 - 5 Hz
Does diathermy use AC or DC?
AC,
DC does not function as a diathermy.
What is the purpose of an isolation transformer in theatre?
To create an unearthed circuit in contact with the patient. This is the sole purpose.
Is electrical impedance directly proportional to frequency in:
- An inductor
- Capacitor
- True
2. False, it is inversely proportional .
what conditions are necessary for laminar flow?
Laminar flow exhists at a low Reynolds number.
Re = (density x velocity x diameter) / viscosity
Therefore at low density, low velocity, small diameter but high viscosity laminar flow can occur.
What is the Bernoulli principle?
An increase in the flow velocity of an ideal fluid will be accompanied by a simultaneous reduction in its pressure.
The total energy of fluid in flow is its kinetic (velocity) plus its potential energy (pressure).
What is the Venturi effect?
An extension of the Bernoulli principle:
The effect by which the introduction of a constriction to a fluid flow within a tube causes the velocity of the fluid to increase, and therefor pressure of the fluid to fall.
This reduced pressure can be used to entrain other fluids or gases into the system in a predictable fashion.
Based upon law of conservation of energy and first law of thermodynamics.
What is the Coanda effect?
The tendency of a stream of fluid flowing in proximity to a convex surface to follow the line of the surface rather than its original course.
Preferentially flow down on limb of the Y-junction rather than being equally distributed.
True or False: in coagulation mode the current waveform comprises short bursts of sine waves.
True.
Coag - short bursts of sine wave.
Cutting - continuous sine wave.
True or false: The frequency of a D.C. signal is 1 Hz.
False, DC has no frequency (0 Hz).
True or false:
In an electrical circuit the energy dissipated by a current I passing through a resistor R is I(squared) R.
Energy dissipated is
V^2/ R
or I^2 R.
True or false:
Laminar flow is more likely to with advancing with a cone front
True
An oxygen-rich gas mixture saturated with water vapour at 20oC, inspired through a tracheal tube, on reaching the alveoli will:
- increase or decrease relative humidity?
DECREASED relative humidity.
- On reaching the alveoli the relative humidity will be less than 100% as the mouth and nares are by-passed by the tracheal tube.
100% relative humidity is achieved in the alveoli.
An oxygen-rich gas mixture saturated with water vapour at 20oC, inspired through a tracheal tube, on reaching the alveoli will:
give up water to the patient?
False.
The amount of water vapour a gas can hold is in relation to its vapour pressure, which is proportional to its temperature, therefore a gas sample, saturated at 20oC, contains less water than a sample heated to 37oC, so the sample described will not give water up to the patient.
