Category Physics

How do Automatic door openers work?

Automatic door openers are usually triggered by a sensor which senses the presence of a person near the door. There are basically two types of sensors which either sense pressure (or weight) or the interruption of a beam of visible or infrared light. In a beam sensor type door opener, the source of the beam and the detector are placed opposite each other in the passageway in front of the door in such a way that the beam crosses the passageway. When the beam is interrupted by a moving person a relay sets the door opening mechanism into operation. If the sensor is of the pressure type it is placed below a movable platform in front of the door. When a person steps on the platform his weight pushes it down slightly activating the pressure sensor and the door opening mechanism.

 

 

How do ATMs work?

An Automatic Teller Machine (ATM) performs simple banking functions such as deposits, withdrawal, cash dispensing, and transfers between accounts.

An ATM is a terminal connected via telephone or dedicated telecommunication lines to larger computer systems that identify the user’s account on the basis of data stored in a magnetic strip on the back of a plastic ATM card commonly known as the credit card. The user operates the systems using an exclusive Personal Identification Number (PIN), assigned to him or her.

 

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How do Spark plugs work?

 

 

 

 

 

 

A spark plug is used in internal combustion engines (except diesel engines) to ignite the fuel air mixture in the cylinder. It consists of an outer steel casing terminating in a bent tip that makes up one of the electrodes and a ceramic insulator sealed into the casing, through which a central electrode passes. The electrodes are separated by a gap that varies from 25 thousandths of an inch to 40 thousandths of an inch. When the engine is running, a pulse of electrical energy at more than 10,000 volts is delivered to the terminal of the plug at the correct moment. The high voltage is supplied by a small generator or a chargeable battery in combination with an induction or ignition coil.

This causes a spark to jump between two electrodes. This spark provides the energy needed to ignite the compressed fuel air mixture in the cylinder to drive the piston. The precise moment at which the spark is produced is pre-set depending on the position of the piston and the compression cycle. 

How is Water purified?

Water supplied to cities and towns is usually taken from rivers or lakes and contain various kinds of pollutants, and so has to be purified. First, the raw water is passed through screens to separate coarse solids and it is then fed into settling tanks where the suspended solids settle out. Some times, substances such as alum are added to aid the settling process.

From the settling tanks the water is sent to sand filter beds -large concrete tanks with thick layers of coarse and fine sand at the bottom. The sand filters remove the remaining suspended matter from the water. Finally, the clear water is treated with chlorine gas in a closed tank to kill bacteria. The purified water is then pumped into tanks for distribution. For industrial use, water is sometimes passed through ion exchangers to remove ions like magnesium and calcium present in hard water.

 

How do Air pollution detectors work?

Air pollution is caused by substances that are not normally part of the atmosphere’s composition. Important air pollutants are sulphur dioxide, nitrogen oxides and carbon monoxide usually emitted in automobile exhausts and power-house smoke. Pollution detectors work by making use of the chemical or physical properties of the pollutants. For example, the detection of nitrogen oxides is based on the emission of light as a result of a chemical reaction. This phenomenon is called chemiluminescence. If nitrogen oxides are present light is emitted which can be detected by a photo detector. Sulphur dioxide is detected by introducing it into a flame and then analyzing the colour produced by an instrument called flame photometer.

Carbon monoxide is detected by emission of infrared radiation of a particular frequency when excited by an arc or a spark. An infrared spectrometer is used to detect the presence of this gas in air.

The quantitative measurement of the gases is based on the intensity of light or spectra they emit. 

How do Night-vision glasses work?

Night vision glasses, used for seeing in the pitch dark night, use the little light available to form an image of sufficient brightness to be seen.

The image is first focussed, as in a camera, on to a window which is coated with special chemicals containing sodium, potassium, cadmium and oxygen compounds which emit electrons when illuminated.

The electrons so emitted are then accelerated by a series of powerful electric fields and made to fall onto another screen coated with a fluorescing chemical which glows recreating a much brighter image of the original scene.

Some night vision glasses make use of infrared radiation emitted by all objects even in the dark. These radiations are amplified in a similar way to make night vision possible.