Storage batteries are devices which act as a storehouse of electrical energy. The electrical energy is stored in the form of chemical charge which is reversible. The most common storage battery is a lead acid accumulator which uses lead as electrode and sulphuric acid as an electrolyte. Initially both the cell electrodes of the battery [...]

Gas mask is a protective device which protects the wearer from breathing in harmless gases. As the polluted air enters the mask, the harmful gases, smoke, dust or chemicals from the air are removed by absorption. The commonly used adsorbent- a mixture of activated charcoal with reactive chemicals, caustic soda fused on pumice stone, fused [...]

A loudspeaker is a device for converting vibrations of electric energy into corresponding vibrations 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 the electric signal [...]

Locks are nothing but special latching devices in which the secured bolt is released only by a specially designed tool, the key. In an order door latch, a bolt is pushed into the hole in the door-frame, and is then secured by turning the key. A similar principle works in a padlock or the portable [...]

Night vision glasses, used for seeing pitch in the 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 [...]