Category Physics

A loudspeaker is a device for converting variations of electric energy into corresponding variations of acoustic energy or sound.

Most speakers have three main parts — a permanent magnet, a coil of wire surrounding the magnet called a voice coil, and a cone-shaped piece of paper or plastic called a diaphragm. When electric signals from an amplifier pass through the voice coil varying magnetic forces are produced in the coil. These magnetic forces interact and drive the coil in a rapid forward and backward motion. The diaphragm which is attached to the voice coil vibrates with it, and in turn sets into vibration the air in contact. Since the surface area of the diaphragm is quite large it sets up vibrations in a large mass of air and the sound produced is quite loud.

Gas mask is a protective device which protects the wearer from breathing in harmful gases. As the polluted air enters the mask, the harmful gases, smoke, dust or chemicals from the air are removed by adsorption. The commonly used adsorbent — a mixture of activated charcoal with reactive chemicals, caustic soda fused on pumice stone, fused calcium chloride and silica gel can remove most kinds of fumes and toxic gases from air. The exhaled air is expelled through a one-way valve in the mask.

All musical instruments produce sound by vibration of something – a string, a membrane or a column of air. A good musical tone is produced when the vibrations have the right frequency (pitch) and right amplitude (loudness).

When a musical instrument is out of tune, it fails to produce sound of the right frequency and an unpleasant sound is produced. These instruments are tuned by making some adjustments. In stringed instruments, the strings (wires) are retuned by tightening or loosening them so that they vibrate with the right frequency when plucked. Similarly, in case of percussion instruments, like tabla, the tension or tautness of the membrane can be adjusted to produce the right sound when struck by hand.

Zipper is a fastening device which consists of two chains of metal or synthetic material, with a series of teeth clamped along the edge of a strong textile tape. Teeth with spiral or ball and pocket devices are inter-locked by means of slider. Stops are fitted at the top and bottom of the tape to prevent the slider from slipping off. Each tooth has a small protrusion on its upper face and a hollow on its lower face. When the protruded portion of teeth in one chain engages with the recesses (hollow) in the other, the zipper fastens. Opposite movement of slide separates the chains.

A lie detector works on the principle that a person who tells a lie is nervous and under stress. Under these conditions his body undergoes some physiological changes.

These include increases in the blood pressure, heart beat rate and perspiration on hands and soles. These changes are monitored and detected by a lie-detector. The person to be examined is made to wear a chest band, a blood pressure cuff and electrodes on his palms.

He is then subjected to a series of questions in order to see his normal reactions.

This is followed by more probing questions. Based on his responses a trained specialist can find out whether the accused person.