Say what meaning is implied in the following word combinations

current flows through the coil

copper coil wound round iron core

to make or break circuit

to store electrical energy

to smooth out pulsating signals

to produce light

 

The following terms are frequently used in electronics. Make sure you know exactly the meaning of each of them. In case of any doubt consult a dictionary.

electronic circuit

capacitor

value of an electronic component

electromagnetic switch

iron core

copper coil

alternating current

primary coil

secondary coil

turn of a coil

logic gate

integrated circuit

induced voltage

variable resistor

light dimmer

fixed resistor

power supply

light emitting diode

oscillator

 

What reasons can be advanced in favor of the idea that: “Electronic is a wonderful world which inhabits intricate devices and gadgets that help people to live and work”. Work in groups of three.

Render the meaning of highlighted paragraphs

 

TYPES OF CAPACITORS

Read the text. Tell the class what you’ve learnt about the evolution of capacitors.

Types of capacitors

A capacitor is a device that stores electric charge. It consists of two electric conductors separated by insulating material called a dielectric. The ability of a capacitor to store charge is indicated by its capacitance, the ratio of the charge it stores to the voltage it gains as a result. Capacitors can take a number of forms, depending on their use.

The first form of the capacitor was the Leyden jar. This capacitor consisted of a glass jar with metal foil coating on the inside and outside; the glass of the jar formed the dielectric. The nature of the equal and opposite charges on the coating was correctly interrupted by Benjamin Franklin.

A parallel-plate capacitor consists of two conducting plates separated by an insulator from two lead plates separated by a glass sheet.

The capacitance of a parallel-plate capacitor is directly proportional to the area of the plates, inversely proportional to their distance apart, and depend on the dielectric. It is given by the formula C=A/4πε ₀ ε _rd, where C is capacitance, A is the cross-sectional area, ε₀ is the permittivity of free space, and ε_r is the relative permittivity of the dielectric.

According to the equation above, one way of changing the capacitance is to vary the area of the plates. This is the basic of the variable capacitor.

Turning the screw (left) changes the area of overlap of the interleaved plates (right).

Variable capacitors of small capacitance can be made using two sets of interleaved plates. One set is fixed and the other can rotate around a common axis, varying the area of overlap between the plates, and thus the capacitance. Variable capacitors can also be made as two cylinders, one sliding inside the other.

The capacitor equation shows that another way to vary capacitance is by varying the distance between the capacitor plates. The equation suggests that a high capacitance could be achieved if the dielectric were very thin. Electrolytic capacitors used an extremely thin (about 0.025 mm) dielectric of aluminium oxide. It is formed by electrolysis: a small current is passed through the electrolyte (usually ammonium borate) placed between the aluminium tubes that are coaxial (share the axis). Since the dielectric of an electrolytic capacitor is so thin, quite high values of capacitance can be achieved with a relatively small capacitor.

It is very important to connect electrolytic capacitors according to the polarity (positive and negative connections) marked on their case. Otherwise, a reversal of voltage can cause breakdown of the dielectric layer, permanent damage, and sometimes even a small explosion. For this reason, electrolytic capacitors should be used only in direct-current circuits.