VERIFICA ORALE INGLESE
A Simple circuit
An electric circuit is the foundation of every electrical or electronic application. It
consists of three main components:
- A power source (such as a battery or generator), which generates an
electromotive force two drive the current.
- A load (like a bulb or motor) that uses the electrical energy to perform a useful
function, such as producing light or mechanical motion.
- A connection (such as a wire or cable) that links the power source and the load.
Circuits often include additional components to control the ow of current, such
as:
- A switch, which can open or close the circuit, allowing or preventing the current
from owing. An open switch creates an "open circuit," stopping the current.
- A fuse, which acts as an automatic switch that opens the circuit if excessive
current ows, preventing overheating or re hazards.
To regulate current, a resistor can be added in series with the load.
Superconductors and Semiconductors
Dividing materials into conductors and insulators is an oversimpli cation, as
semiconductors exist in between.
The advantage of semiconductors is their ability to have their electrical behavior
modi ed, making them essential in electronics. Similarly, superconductors, which
have no electrical resistance, could revolutionize energy delivery, transport, and
e ciency. However, they only function at extremely low temperatures, around
-150°C. American Superconductor developed exible ceramic superconductors,
which are now used in applications like maglev trains and ship motors. Despite
their potential, the need for cooling limits their use. Superconductors are also
crucial in MRI and NMR devices, as they generate stable, high-intensity magnetic
elds for diagnostic equipment.
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New ways of lighting
Traditional incandescent bulbs, invented by Edison, are being replaced by energy-
saving uorescent bulbs, LEDs, and OLEDs due to their ine ciency—95% of
energy is wasted as heat. Compact uorescent lamps, developed in the 1940s,
use 80% less power and last over four times longer but have drawbacks such as
slow illumination, ickering, and toxic mercury content. LEDs, created in the
1960s, are highly e cient, producing bright light with minimal heat or ultraviolet
radiation, but require integrated converters for AC power. OLEDs, a newer
technology, use thin organic lms to produce soft, di use light and are already
used in screens. Both LEDs and OLEDs are costly but durable, with prices steadily
decreasing.
E ects on human body
To prevent risks when working with electrical systems, it is crucial to understand
the hazards and follow safe practices. Electrical harm is caused by current owing
through the body, not by voltage itself. Wearing insulating shoes is recommended
to reduce risks, as they increase resistance and limit current ow in case of
accidental contact with live objects.
An additional safety measure is the residual current device (RCD), which detects
current leaks above 30 mA, such as those caused by ground faults or current
passing through the human body, and interrupts the circuit. However, the RCD is
not infallible, as currents of 300 mA can still be dangerous if sustained. For
maximum safety, the main switch should always be turned o before handling
electrical wires.
Edison
Thomas Edison revolutionized modern life by helping to develop a network of power
cables and numerous electrical devices. When he left school in 1859, electrical equipment
relied on low-powered batteries, but by his death, electricity was widely available in
Europe and North America, transforming daily life. Many modern appliances either
originated from Edison's ideas or were improved by him to become practical. He
held patents for various inventions, showcasing his inventive genius.
Current, Voltage and resistance
The ow of electric current in a circuit depends on the voltage and the resistance.
This can be compared to a plumbing system: voltage is like water pressure,
current is the ow of water, and a resistor is like a mill wheel that limits the ow.
Resistance, measured in ohms, restricts current ow, similar to how the mill wheel
resists water ow more than the pipe. The relationship between voltage, current,
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and resistance was discovered by Georg Ohm in 1827, expressed as Ohm's Law:
(V = IR), where voltage equals current times resistance.
