Diesel Engine:- The diesel engine was developed by Rudolf Diesel in 1893.  It is a low cost internal combustion engine with high efficiency. It consists of a cylinder with air-tight piston along with two valves. When the piston compresses the mixture of air and diesel; the temperature increases to 600°C producing ignition. The gases formed by ignition expand and push the piston out with a great force. It is connected with the gear which in turn is connected with the wheels which are set in motion. Finally the piston forces the inner gases out through another valve. This cycle is repeated again and again.

Safety Lamp:- The Safety Lamp was invented by Sir Humphrey Davy to save the lives of the miners working in the mines. It consists of an ordinary lamp surrounded by a cylinder of wire gauze instead of glass chimney. The inflammable gases from the mine enter the gauze and burn inside the lamp with a blue flame. The gauze conducts the heat so well that the temperature outside and near the gauze never reaches the ignition point. The safety lamps are used mostly in coal mines designed to operate in air that may contain coal dust, methane, or firedamp, all of which are potentially flammable or explosive.

Dynamo:- Dynamo is a device which transforms mechanical energy into electrical energy. The mechanical energy needed is obtained generally from a water turbine. It consists of a rectangular coil of wire called armature which rotates in a strong magnetic field created by electro magnet. As the coil rotates a current is induced in the coil. The dynamo was invented by Michael Faraday in 1831.

Lightning Conductor:- The lightning conductor is a metal rod or conductor mounted on top of a building and electrically connected to the ground through a wire, to protect the building in the event of lightning. When heavily charged cloud comes over the building, it induces an opposite charge on the upper end of the pointed rod of the lightning conductor and similar kind of charge is repelled into the earth. If the cloud is positively charged, the pointed end becomes negatively charged. From the pointed ends charge begins to leak setting up an electric wind which neutralizes some of the charge of the cloud, thus decreasing the potential difference. Thus lightning will not strike the building. If lightning strikes the building it will preferentially strike the rod, and be conducted harmlessly to ground through the wire, instead of passing through the building, where it could start a fire or cause electrocution. The lightning conductor was invented by Benjamin Franklin of America in 1749.

Periscope:- A periscope is an instrument for observation from a concealed position. In its simplest form it consists of a tube with mirrors at each end set parallel to each other at a 45-degree angle. More complex periscopes, use prisms instead of mirrors, and provide magnification, operate on submarines. A periscope is used by crew in submarines to see the surface of the water. The head of the instrument is visible over the surface of water. Light from an object is twice or thrice reflected through a rectangular pipe in which mirrors are fixed and reaches the eye-piece in which the image is seen. In 1854, E.H. Marie-Davy invented the first naval periscope. Simon Lake used periscopes in his submarines in 1902.

Radar:- Radar is an abbreviated form of Radio, Angle, Direction and Range. It is an object-detection system which uses electromagnetic waves—specifically radio waves—to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A narrow beam of high frequency radio-waves is sent in all directions from the instrument. The invisible object in the space reflects these waves back. Radar receives these waves and by the time taken by them determines the distance and direction of the invisible object. The term RADAR was coined in 1940 by the U.S. Navy as an acronym for radio detection and ranging.

Rocket:- The underlying principle of the flight of a rocket is Newton’s Third law of Motion- to every action there is an equal and opposite reaction. It is a self-propelled vehicle which depends upon the force provided by a fuel carried along with it. As the fuel burns, products of combustion are forced out at terrific speed at the rear of the vehicle and reaction imparts motion to it in the forward direction. It has its own oxygen supply for burning the fuel and therefore, there is no dependence on air for combustion or propulsion.