Electricity
Ohm’s law may be stated in the form: “the current flowing in a circuit is the potential difference divided by the electrical resistance in the circuit”. If a person whose hand-to-hand resistance is 80,000 Ω touches a live wire (attached to 240 V mains supply) and a wall at the same time, what is the magnitude of the current that will flow through the chest?
3 mA
30 mA
300 mA
3000 mA
3 mA
Ohm’s law as stated is: I = V ÷ R putting in the numbers gives: I = V ÷ R = 240 ÷ 80,000 = 0.003A = 3 mA.
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Choose the alternative which correctly completes the following sentence: “There are two types of electric charge called:A. Protons and electrons and they attract each other”.
B. Positive and negative and they attract each other”.
C. Anions and cations and they repel each other”.
D. Electrons and ions and they repel each other”.
What are the deflections seen on an electrocardiogram trace due to?
A. Pressure differences created by ventricular contraction
B. The closing and opening of heart valves
C. The de- and repolarisation of the cells of the myocardium
D. Variation in the electrical properties of oxygenated blood and deoxygenated blood as it moves through the heart
Why does a correctly installed earth wire provide protection against electrocution by a faulty electrical device? Because:
A. It is made of thick copper wire so presents almost zero resistance.
B. A fuse is located on the earth wire which will “blow” if excessive current flows.
C. The earth wire is connected to the ground and to the metal case of the appliance.
D. The on/off switch is on the earth wire so that power can be turned off.
For patients in a medical treatment room that are receiving an intravenous infusion driven by an electrical pump, what term is used to describe the electrical supply to the room?
A. Cardiac-protected
B. Body-protected
C. Equipotentially earthed
D. Double insulated
In an Australian domestic AC electrical circuit, what is the potential difference (voltage) in the three wires?
A. Active wire oscillates between +240 V and −240 V, while neutral and earth are both at 0 V.
B. Neutral wire at −240 V, active at +240 V, earth at 0 V.
C. Active wire at +240 V, while neutral and earth are both at 0 V.
D. Neutral wire and active wire both at +240 V, earth at −240 V.
The potential differences generated by the heart muscle as it contracts and relaxes can be measured by placing electrodes on the surface of the body. What is the record of these electrical events correctly called?
A. An electrocardiogram
B. Limb lead II
C. An electrocardiograph
D. An EEG
In an electrical device, a correctly installed earth wire provides protection against what?
A. The electrical device receiving too high a current.
B. It protects the fuse or circuit breaker from too much current.
C. Electrocution of a person touching the faulty electrical device.
D. It protects against stray currents that may exist in the ground (the soil).
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