Tue16November0750PM 6

A direct current (DC) cardiac defibrillator is charged using 240 volts alternating current (AC) from a wall socket.

Which of the following electrical components converts AC to DC?

(Please select 1 option)

Rectifier This is the correct answer

Inductor

Step-down transformer Incorrect answer selected

Capacitor

Step-up transformer

Explanation

Alternating current (AC) is a flow of current along a conductor that constantly changes direction. The amplitude of the current changes with time or the angle of rotation (). The shape of one full cycle is 360° (or 2p) is a sinusoid. Mains electricity has a frequency of 50 Hz and the current driven by a potential difference of 240 volts.

Direct current (DC) is a flow of current along a conductor in one direction only. Batteries or cells supply DC.

Full wave rectifier:

This is an electrical component that is composed of four diodes. Diodes are made of semiconductor materials that can allow current to flow in one direction and block current in the opposite direction. Alternating current (AC) passing through this arrangement of diodes produces direct current (DC).

Transformers:

A transformer is an electrical component with an iron core that transfers energy between two or more circuits by electromagnetic induction. The iron core is used to concentrate the magnetic flux. A typical transformer will have a primary (input) wire coil and a secondary (output) wire coil. The difference between the input and output voltage will depend on the differences in the number of turns of the wire between the primary and secondary coils. Transformers are used to isolate circuits, change impedance and alter voltage output. Transformers no not convert AC to DC.

Step-down transformer:

Has more turns of wire in the primary coil than the secondary coil. The induced voltage by electromagnetic induction is smaller in the secondary coil. For example, the input might be 240 volts AC but the output only 12 volts.

Step-up transformer:

There are more turns of wire in the secondary coil than the primary coil. The induced voltage is larger in the secondary coil. This type of transformer is used in the defibrillator to increase the voltage input of 240 volts to 6000 volts to enable the charging of a capacitor.

Capacitor:

Is an electrical component that stores charge in the form of an electrostatic field and is the key component of a cardiac defibrillator. It consists of two metal plates separated by insulator (dielectric). Capacitance is measured in farads (typically µF, pF or nF). 1 farad = potential difference of 1 volt across plates. Capacitors are used to 'smooth out' rectified AC voltage to produce battery-like DC voltage. Capacitors do not directly convert AC to DC.

Inductor:

In its simplest form is a wire, often coiled around an iron core. An electromagnetic force generated when a potential difference is applied across the wire produces a 'back' electromotive force (emf) sufficient to slow the passage of electrons and therefore current.

Answer Statistics

1

36%

2

14%

3

18%

4

28%

5

7%

Times answered: 242