5 & 6- Optics: Concave and Convex Glasses; Pressure Cookers, DTH, Radar, Refrigeration UPSC Notes | EduRev

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UPSC : 5 & 6- Optics: Concave and Convex Glasses; Pressure Cookers, DTH, Radar, Refrigeration UPSC Notes | EduRev

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5: OPTICS: CONVEX AND CONCAVE GLASSES: DIFFERENCES, APPLICATIONS, AND REFRACTIONS

Concave lens is the one whose curved surface is bent inside. It diverges the rays from the principal axis. It generally forms virtual and erect image i.e. image on the same side of the object. This image can't be taken on the screen. Convex lens is the one whose curved surface is bulged out. Simplest example is dewdrop on a leaf. It generally gives real and inverted image and has a capacity to magnify the image.                                                                                            

USES

1. Both concave and convex lenses are used in glasses

2. A microscope, like a reflecting telescope, uses a concave mirror

3. A plane mirror, and a convex lens

4. A refracting telescope uses two convex lenses to magnify images in the sky

5. Binoculars use concave lenses to improve detail.

6. Convex mirrors are often found on the passenger sides of motor vehicles. These mirrors make objects appear smaller than they really are. Due to this compression, these mirrors to reflect a wider image area, or field of vision.

7. Convex mirrors are often placed near ATMs to allow bank customers to see if someone is behind them. This is a security measure that helps keep ATM users safe from robbery of any cash withdrawals and helps keep ATM users' identity more secure.

8. Two convex mirrors placed back to back are used to make a magnifying glass.

9. Concave mirrors are used in vehicle headlights to focus the light from the headlight. The light is not as diffused and the driver can see better at night.

10. Concave mirrors are used to focus light for heating purposes.

 

6: PRESSURE COOKERS, DTH TV, RADAR, OVEN, NIGHT VISION GOGGLES, REFRIGERATION

PRESSURE COOKER 

Pressure cooking is the process of cooking food, using water or other cooking liquid, in a sealed vessel — known as a pressure cooker, which does not permit air or liquids to escape below a pre-set pressure. Pressure cookers are used for cooking food quicker than conventional cooking methods, which also saves energy.

Pressure cookers heat food quickly because the internal steam pressure from the boiling liquid causes saturated steam (or "wet steam") to bombard and permeate the food. Thus, higher temperature water vapour (i.e., increased energy), which transfers heat more rapidly compared to dry air, cooks food very quickly.

Pressure cooking allows food to be cooked with greater humidity and higher temperatures than possible with conventional boiling or steaming methods. In an ordinary non-pressurised cooking vessel, the boiling point of water is 100 °C (212 °F) at standard pressure; the temperature of food is limited by the boiling point of water because excess heat causes boiling water to vaporize into steam. In a sealed pressure cooker, the boiling point of water increases as the pressure rises, resulting in superheated water. At a pressure of 15 psi (103 kPa) above atmospheric pressure, water in a pressure cooker can reach a temperature of up to 121 °C (250 °F).

Some foods are not recommended for pressure cooking in liquid. Such foods could expand too much, froth, and sputter, which can result in blocking the steam vent. Examples include macaroni, cranberries, and cereals such as oatmeal.

 

DTH TV- DIRECT TO HOME TELEVISION  

DTH stands for Direct-To-Home television. DTH is defined as the reception of satellite programmes with a personal dish in an individual home.

DTH does away with the need for the local cable operator and puts the broadcaster directly in touch with the consumer. Only cable operators can receive satellite programmes and they then distribute them to individual homes.

A DTH network consists of a broadcasting centre, satellites, encoders, multiplexers, modulators and DTH receivers.

A DTH service provider has to lease Ku-band transponders from the satellite. The encoder converts the audio, video and data signals into the digital format and the multiplexer mixes these signals. At the user end, there will be a small dish antenna and set-top boxes to decode and view numerous channels. On the user's end, receiving dishes can be as small as 45 cm in diameter.

 

HOW DOES DTH REALLY  DIFFER FROM  CABLE TV ?  

The way DTH reaches a consumer's home is different from the way cable TV does. In DTH, TV channels would be transmitted from the satellite to a small dish antenna mounted on the window or rooftop of the subscriber's home. So the broadcaster directly connects to the user. The middlemen like local cable operators are not there in the picture.

DTH can also reach the remotest of areas since it does away with the intermediate step of a cable operator and the wires (cables) that come from the cable operator to your house. As we explained above, in DTH signals directly come from the satellite to your DTH dish.

Also, with DTH, a user can scan nearly 700 channels!

 

RADAR 

Radar is an object detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.

Radar was secretly developed by several nations before and during World War II. The term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging.

The modern uses of radar are highly diverse, including air traffic control, radar astronomy, air- defence systems, antimissile systems; marine radars to locate landmarks and other ships; aircraft anti-collision systems; ocean surveillance systems, outer space surveillance and rendezvous systems; meteorological precipitation monitoring; altimetry and flight control systems; guided missile target locating systems; and ground-penetrating radar for geological observations. High tech radar systems are associated with digital signal processing and are capable of extracting useful information from very high noise levels.

Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "liar", which uses visible light from lasers rather than radio waves.

The first use of radar was for military purposes: to locate air, ground and sea targets. This evolved in the civilian field into applications for aircraft, ships, and roads.

The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended.

 

REFRIGERATION  

Refrigeration is a process in which work is done to move heat from one location to another. The work of heat transport is traditionally driven by mechanical work, but can also be driven by heat, magnetism, electricity, laser, or other means. Refrigeration has many applications, including, but not limited to: household refrigerators, industrial freezers, cryogenics, and air conditioning. Heat pumps may use the heat output of the refrigeration process, and also may be designed to be reversible, but are otherwise similar to refrigeration units.

The measured capacity of refrigeration is always dimensioned in units of power. Domestic and commercial refrigerators may be rated in kJ/s, or Btu/h of cooling. For commercial and industrial refrigeration systems, most of the world uses the kilowatt (kW) as the basic unit of refrigeration. Typically, commercial and industrial refrigeration systems in North America are rated in tons of refrigeration (TR).

A refrigeration system's coefficient of performance (Cope) is very important in determining a system's overall efficiency.

 

METHODS OF REFRIGERATION CAN BE CLASSIFIED AS NON -CYCLIC, CYCLIC, THERMOELECTRIC AND MAGNETIC  

In non-cyclic refrigeration, cooling is accomplished by melting ice or by subliming dry ice (frozen carbon dioxide). These methods are used for small-scale refrigeration such as in laboratories and workshops, or in portable coolers.

This consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic power cycle.

The vapour-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems.

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