Category Everyday Science

How a quartz watch tells the time?

The exquisite workmanship of the traditional mechanical wristwatch has given way to the magic of the microchip. In the quartz watch, a vibrating crystal has taken over the role of timekeeper from the traditional finely tuned balance wheel ad hairspring. Minute electronic circuits control its operations.

A quartz crystal vibrates at an unvarying rate when an electric current is passed through it. The man-made quartz crystals used in watches are usually designed to vibrate 32,768 times a second when stimulated by the current from a battery. These vibrations produce electric pulses, and as the pulses travel through the electronic circuits of the microchip, their rate is successively halved in a series of 15 steps. The result is one pulse per second. Each one-second pulse triggers the chip to send signals to the digital display to advance the numerals one second.

The chip also uses the pulse as a base for other counting circuits, such as those that display hour and date, and to control the alarm signal.

Many modern quartz watches display the time in digits on a liquid crystal display (LCD). The liquid crystals are sandwiched between a reflective bottom layer and a top layer of polarised glass, and transparent electrical conductors separate them into segments. Each digit is formed from segments – up to seven are normally used, all seven being used for figure 8.

The liquid crystals rearrange their molecules according to their electrical state. Where the conductors carry no charge, light through the sandwich is reflected out again, so the display is blank. When the conductors are charged by an electric pulse, the molecules in the affected segments realign and twist the light away from the reflective surface, so the segments appear dark.

 

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What are Binary numbers?

Because we have eight fingers and two thumbs, it seems natural for human beings to count in tens. It is just as natural for a computer to count in twos, for it has to decide between ‘yes’ or ‘no’ for every step in a process.

In everyday numbers, the digits from 0 to 9 are read from left to right and are based on the power of ten. For example, 110 is one hundred, ne ten, and no units.

The binary system uses only two digits: 0 and 1. Numbers are read from right to left and are based on the power of two. Moving from the right, each digit doubles in value, 1, 2, 4, 8, 16, and so on. 

Words fed into a computer are stored as binary numbers. If text such as LOAD”FILE in BASIC, computer language is keyed in, the word LOAD could be processed.

 

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How a camera focuses automatically?

In the split second between the pressing of the shuttle release and the opening of the shutter, an automatic camera measures the distance between the lens and the subject and positions the lens to give sharp focus.

Most compact cameras have a tiny electric motor driving a transmitter that emits a beam of infrared light. The transmitter is linked to the lens, which moves in or out as the beam scans – focusing from near to far. The beam reflects back from objects to the camera, and a sensor monitors its signals and stops the transmitter when the strongest signal shows that the lens is in focus. This automatically triggers the shutter.

Some instant cameras have ultrasonic focusing similar to the echolocation scanning system bats use to navigate. A gold-plated disc (the transducer) sends out ‘chirps’ too high to be heard by human ears, each lasting 1/100th of a second. The disc receives the chirp echoes from the subject, and a built-in microcomputer measures the time each chirp takes to go out and come back. From this it calculates the distance to the subject.

SLR (single-lens reflex) cameras with an auto-focus use what is known as an electronic phase detection system. In this, light entering through the lens is separated into two images. A sensor measures the distance between the two images, which are a specific distance apart when the lens is in focus. If the distance is not correct, the sensor causes a motor to move the lens.

 

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What is laser?

The word ‘laser’ is made up from the initials of the words that describe its action, Light Amplification by Stimulated Emission of Radiation. An American physicist, Theodore H, Maiman, invented and first demonstrated it in 1960.

One of the earliest types of laser was the solid ruby laser, made from a ruby crystal or an artificial ruby rod. The chromium atoms in the ruby are stimulated to emit the laser light. An electronic flash tube coiled round the rod gives out intense bursts of light that excite the chromium atoms from a low-energy to a high-energy state.

After a few thousandths of a second, the atoms revert to their normal state, spontaneously emitting an energy package known as a photon. When a photon strikes another chromium atom still in a high-energy state, it stimulates it to emit an identical photon.

The parts of identical photons travel together in the same direction and exactly in step. The beam is built up by millions of them being reflected back and forth between mirrors at each end of the ruby rod. It finally emerges through a half-silvered mirror at one end, in bursts (pulses) of red light of about one-thousandth of a second.

The laser’s power lies not in the amount of its energy, but in the concentration. The beam is very straight, and the photons – all strike the same surface at the same moment. a laser beam can be powerful enough to burn a hole in a steel plate, or delicate enough to be used in eye surgery.

The smallest lasers now in use are semiconductor lasers. They produce an invisible infrared beam when charged with an electric current.

 

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How do they know the continents are drifting?

As long ago as 1620, the English philosopher Francis Bacon pointed out the close fit between the coastlines of South America and Africa. The shapes suggested that they had once been joined but had drifted apart.

In 1912 the German meteorologist Alfred Wegener put forward detailed arguments in support of the theory. But it was not proved to the satisfaction of most geologists until the 1960s.

The fit between the two continents is good, particularly the continental edge rather than the shorelines. Their shape has been altered by the eroding effects of tides. But the continental outlines where the ocean is 3000ft (900m) deep show the average ‘misfit’ when joined to be only about 50 miles (80km).

Other evidence that the continents were once linked includes common geological features, such as similar types of rock of a similar age. And many plants and creatures appear to share a common origin. For example, many freshwater fish in South America are closely related to African species, and it is difficult to accept that they could have swum the Atlantic Ocean.

The guinea pig is found in the wild in both Africa and South America, but nowhere else. Also, monkeys are indigenous only in those continents and it is unlikely they would have evolved independently in each place.

 

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How the speed of light was measured?

A French physicist, Jean Foucault, measured the speed of light remarkably accurately in the mid-19th century, using two mirrors set 66ft (20m) apart.

One mirror was fixed and another rotated at 800 revolutions a second. Beams of light were directed at the rotating mirror. When a light beam hit the mirror while it was at just the right angle, it was reflected to the fixed mirror, bounced back to the rotating mirror and then reflected back to the source.

In the time it took to make the return trip between the mirrors, the rotating mirror had turned through a small angle so the beam that returned to the source deviated slightly from the original path.

By using the deviation of the beam to measure the angle through which the mirror had moved, and knowing the speed of rotation, Foucault could work out how long the light had taken for its trip, and its speed. Foucault’s final result, reported in 1862, worked out at 187,000 miles a second (300,939km a second).

Foucault’s method was refine in the 1920s by Albert Michelson, an American physicist, who sent light through a vacuum tube a mile (1.6km) long to remove the effect of air on its speed. Modern measurements have refined the figure to 186,282 miles (299,793km) a second.

 

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