Electricity MCQs - MCQtimes.com

In an Australian domestic AC electrical circuit, what is the potential difference (voltage) in the three wires?

Active wire oscillates between +240 V and −240 V, while neutral and earth are both at 0 V.

Neutral wire at −240 V, active at +240 V, earth at 0 V.

Active wire at +240 V, while neutral and earth are both at 0 V.

Neutral wire and active wire both at +240 V, earth at −240 V.

In a domestic supply, the potential of the active wire oscillates (alternates) from about +270 V to 0 V to −270 V (the rms values are ±240 V), while the neutral wire is at 0 V. The earth wire is for safety purposes, kept at 0 V to provide a low resistance path to the ground in the case of a fault.

Author: rikazzz Comment

Electricity

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?

Cardiac-protected

Body-protected

Equipotentially earthed

Double insulated

The catheter that delivers the IV infusion passes through the skin to enter a vein. This makes a direct electrical connection to the heart (via the blood). Consequently the patient must be protected against micro-electrocution and be treated in a cardiac-protected room. An equipotential earthing system is part of the installation of a cardiac-protected area.

Author: rikazzz Comment

Electricity

Why does a correctly installed earth wire provide protection against electrocution by a faulty electrical device? Because:

It is made of thick copper wire so presents almost zero resistance.

A fuse is located on the earth wire which will “blow” if excessive current flows.

The earth wire is connected to the ground and to the metal case of the appliance.

The on/off switch is on the earth wire so that power can be turned off.

A faulty appliance (with a metal case) may become “live”. If it does, a large current may flow through the earth wire, rather than through a person touching the case. The large current will blow the fuse which is located on the active wire (as is the on/off switch).

Author: rikazzz Comment

Electricity

What are the deflections seen on an electrocardiogram trace due to?

Pressure differences created by ventricular contraction

The closing and opening of heart valves

The de- and repolarisation of the cells of the myocardium

Variation in the electrical properties of oxygenated blood and deoxygenated blood as it moves through the heart

The P wave is due to the depolarisation of the atria, the QRS due to the depolarisation of the ventricles and the T due to the repolarisation of the ventricles.

Author: rikazzz Comment

Electricity

Choose the alternative which correctly completes the following sentence: “There are two types of electric charge called:

Protons and electrons and they attract each other”.

Positive and negative and they attract each other”.

Anions and cations and they repel each other”.

Electrons and ions and they repel each other”.

The two types of charges are positive and negative which may exist on a variety of particles such as those named in the other choices.

Author: rikazzz Comment