Define Illumination? Explain the laws of illumination? Illumination- - - PowerPoint PPT Presentation

Define Illumination? Explain the laws of illumination? Illumination- The luminous flux falling per unit area of a surface. Laws of Illumination: 1) Inverse square law- According to this law, the illumination of a

surface is inversely proportional to the square of the distance between the source and the surface.

2) Lambert cosine law- The illumination at any point on a surface

is proportional to the cosine of the angle between the normal at that point and the direction of light flux i.e.

Define

1) Candle power- It is defined as the number of lumens emitted by a source per unit solid angle in a given direction. 2) Solid angle- The angle subtended by an area of a solid body at the centre of the body is called solid angle. 3) Luminous flux- It is the light energy radiations coming from a body e.g. electric lamp. 4) Luminous intensity- It is the luminous flux emitted by a source per unit solid angle. 5) Luminous efficiency- The efficiency of a source to convert supplied power (in watts) into lumens of light is called luminous efficiency.

6) Illumination- The luminous flux falling per unit area of a surface. 7) Space height ratio- The ratio of two success source to their mounting height is called space height ratio. 8) Glare- Reflection on the eye is called glare. 9) Reflection factor- It the ratio of reflected light to the incandescent light is called reflection factor. 10)Shadow- are produced when some opaque body comes in the light source. 11)Lux- is the unit of light intensity, one lux is equal to one lumen per meter square falling on the surface. 12)Lumens- cnadle power * solid angle.

Discharge lamps

Incandescent lamps have a very low lumens output. Moreover they give yellow light, which creates strain in

• ur eyes. Discharge lamps have high output and they

produce a light which is pleasing to eyes. The discharge lamps have also two electrodes in a glass envelope with a gas. When electrodes are given supply, the light is produced through gas discharge, (ionization). The colour

• f light produced depends upon the gas or vapour filled

in the lamp.

Factors kept in mind while designing interior lighting

1) Provision of adequate illumination level 2) Uniform illumination 3) Colour of light 4) Shadowless illumination 5) Glare free illumination 6) Mounting height 7) Space height ratio 8) Utilization factor 9) Depreciation factor 10) Efficiency of lamp

How street lighting is done?

Street lighting: has a different design from that of indoor

• lighting. As the area in open, the illumination level

required is low. a) Diffusion principle- The lamps are fitted with suitable reflectors which spread the light as uniformly as possible over the road surface. The road surface appears bright to the observer. b) Specular reflection principle- In this method, light falls

• n an object at a very large angle of incidence and is

therefore reflected at a correspondingly large angle.

A lamp of 500watt have a candle power of 1000 is suspended at a height of 2.5mtr above a working plan. Calculate 1) Illumination directly below the lamp 2) The lamp efficiency 3) Total luminous flux in a radius of 25cm below the lamp? 1) Illumination directly below the lamp 1000/(2.5)2=160 lm/m(2) 2) Lamp efficiency 12566.371/500=25.13 lm/watt 3) Radius A=efficiency* (0.5)2/ 4=0.19m(2) flux=I*A=160*0.19=37.42 lm/m(2)

What is Electrical heating? What are its advantages?

Electrical Heating: Heating by means of converting electricity into heat is called electric heating. Applications of Electrical heating: 1) Cleanliness 2) Ease of control 3) Quick operation 4) Absence of flue gases 5) High efficiency of utilization

Explain high frequency induction heating?

In high frequency heating skin effect plays the major role. According to this, arc has more density near the skin and at the centre the density of current is nearly zero. The skin effect is high at higher frequency and decreases with decreased frequency. In D.C. this effect is absent.

Explain induction heating?

Induction Heating: Heating produced due to eddy currents induced in a inductive core by electromagnetic induction is called induction

• heating. The frequencies employed for eddy current heating are

usually between 10(54) to 10(6) m(2). The depth of penetration of the eddy current into the charge is inversely proportional to the square root of the frequencies.

What is arc welding? What is production of arc welding?

Arc Welding: A process in which welding is done by producing heat from an electric arc between the work and electrode is called arc welding. An arc welding is a fusion welding process. Both a.c. as well as d.c. can be used for the production of the arc. Electric arc is produced when contact is first made between the electrode and workpiece to complete the circuit and then seperating the two by a small distance. Arc is a sort

• f an electric discharge through a path of ionised

particles of air and produces an immense heat if continuous arc is maintained.

Explain various characteristics on which power supply sources for arc welding are based?

The arc has negative resistance characteristics i.e. the resistance of the arc decreases with increases of temperature. The decreased resistance will further increase in current. Due to this characteristic, it is not possible to maintain a steady arc. To overcome this difficulty, the supply to the arc should be such that the voltage falls rapidly with increase in current. In

• ther words, the source of supply should have a dropping characteristics.

Complete note on MIG and TIG welding?

TIG Welding: It is Tunguston Inert gas arc welding. It is a type of arc welding in which an inert gas shield is provided around the arc. The arc is created between tunguston electrode and work piece. In TIG welding electrodes are non-consumable. In this process, electrode is held in an electrode holder. The electrode holder holds the electrode and ensures the supply

• f inert gas around the electrode. This creates an inert

atmosphere around the electrode. Cooling during welding can be done by supplying water on air through the electrode

• holder. In this process no filler metal is used. This type of

welding is applied to join aluminium-alloy, copper-alloys, magnesium-alloys, nickel-alloy etc. It protects the joint against oxidation. It also avoids the formation of nitrides.

MIG Welding: It is gas metal arc welding. In MIG welding a consumable electrode in an inert gas atmosphere is used to produce a weld. Therefore it is also called metal inert gas (MIG) welding. Consumable electrodes are used in MIG

• welding. D.C. with straight polarity type of power supply is

required for MIG welding. Inert gas like Argon, Helium, Carbon-Dioxide or a mixture of these gases. Now CO2 is most widely used. In this process, a continuous wire acts as an electrode. This wire is held by an electrode holder which feeds the wire into the arc space continuously. Feeding of the wire is controlled by an electric motor. The electrode holder also ensures the supply of inert gas to create an inert atmosphere around the arc. This type of welding process is applied for joining low temperature alloy sheets, aluminium alloys, magnesium alloys and copper alloys.

What is Electro-deposition? What are its applications?

Electro-deposition: The process of depositing a coating of one metal with other metal by electrolytic process is called electro-deposition. Applications of Electro-deposition are: 1) Electroplating- Electroplating is the process in which a superior metal is deposited on an inferior metal through electrolysis i.e. nickel or chromium is deposited on articles of

• iron. Gold or silver is deposited on copper. The purpose of

electroplating may be repair of worn out articles, decoration

• r ornamentation. The article is made cathode, the metal is

deposited is made anode and electrolyte is the salt solution

• f metal to be deposited.

2) Anodising- Anodising is a process in which film of oxide is produced artifically by the passage of current. This is very hard coating and is formed to protect the base metal from

• corrosion. It also has a decorative appearance. This is also

used to produce decorative articles by giving separate

• colours. The articles to be anodized is thoroughly cleaned

and made anode carbon rod is made cathode. The required voltage is about 10-50 volts. 3) Electro-forming- The reproduction of objects by elecro- deposition on some sort of mould or form is known as electro-forming. In the reproduction of coins, models, engravings etc, a mould is made by impressing the object in

• wax. The surface of the mould which bears the exact

impressions of the object is coated by powdered graphite in

• rder to make it conducting. The mould is dipped in an

electroforming cell as a cathode.

4) Manufacture of chemicals- There are many industrial applications of electrolysis in the manufacturing of chemicals such as production of caustic soda, potassium permagnet, chlorine, oxygen and hydrozen. The most important out of them is manufacture caustic soda by the electrolysis of brine. 5) Extraction and refining of metals- Electrolysis processes are used in the extraction of metals like aluminium, copper, magnesium, sodium and zinc. In the process of refining of metals, the impure metal obtained from its ore from metallugrical reduction is made anode. The salt of the metal to be refined is made electrolyte. Whenever potential difference is applied across the electrodes, the impure metal gets dissociated into positively and negatively charged ions. The positively charged ions consists of pure metal. Since positively charged ions are attracted by the cathode, these ions give their positive charge to the cathode.

What is electrolysis? Explain the laws

• f electrolysis?

Electrolysis: The process of decomposition of electrolyte by the passage of electric current through them is called electrolytic process or electrolysis. There are two types of laws of electrolysis: 1) First Law- According to this law, “The amount of substance liberated at an electrode is directly proportional to the quantity of electricity passed”.

• 2) Second Law- According to this law, “if same quantity of

electricity is passed through different electrolytes, then the amount of substances liberated at the respective of electrodes are in the ratio of their equivalent masses”.

Difference between resistance welding and arc welding?

Resistance welding

• Heat is mainly developed due

to flow of current through the contact resistance.

• Supply employed is usually

a.c.

• Low voltage is required.
• Cannot be used for repair

work.

• Power factor is fairly good.
• Most suitable for mass

production.

• Weld is obtained at low

temperature.

Arc welding

• Heat is developed due to an

arc formed between the electrodes and work piece.

• Supply can be both a.c. and

d.c.

• High voltage is required for

striking.

• Most suitable for repair work.
• Power factor is very low.
• Not suitable for mass

production.

• The arc temperature is very

high.

Difference between A.C. welding and D.C. arc welding?

A.C. arc welding

• A welding transformer is

cheaper than a d.c. generator.

• A welding transformer is

simpler in operation than a d.c. generator welding set.

• It is suitable for use at low

current with small diameter electrodes.

• Maintenance of a short

arc is difficult. D.C. arc welding

• A d.c. generator is costlier

than a welding transformer.

• A generator welding is more

cumbersome in operation.

• It is better suited for use at

low current with small diameter electrodes.

• Maintenance of a short arc

is easier.

What is refrigeration and air conditioning?

Refrigeration: It is defined as the process of removing heat from a substance to be cooled and passing it on to some another substance under controlled conditions. It is includes the process of lowering and maintaining the temperature of a cooled body below the general temperature of its surroundings. Air Conditioning: Air conditioning means the simultaneous control of heating/cooling, cleaning, humidifying and air circulation either for comfort human beings or of animals or for the proper performance of some industrial or scientific process.

Explain in detail vapour compression cycle in Refrigerator?

The vapour compression cycle is chiefly composed of four stages i.e. compression, condensation, expansion and

• vapourisation. The purpose of refrigeration cycle is to remove

heat from refrigerant by again putting it into liquid form so that it may be used again and again.

The four main stages of vapour compression cycle are: 1) Vapourisation- From the expansion valve, the pressure refrigerant at low temperature enters the evaporator which is placed near or around the material to be cooled down. Before entering the evaporator, the refrigerant is in the liquid state and when it absorbs heat from the material to be refrigerated it is formed from a liquid to a vapour state. 2) Compression- The compressor draws the vapours from the evaporator through the return piping and then compresses these vapours until their temperature is raised above that of the condensing medium. The compressor is driven by external mechanical energy which may be supplied by an engine or electric motor. Generally, electric motors are employed for this purpose.

3) Condensation- When the temperature of the vapour is raised above that of the condensing medium by the compressor, then the heat of vaporization will flow from the vapour to the condensing medium to condense the refrigerant to a high pressure liquid. The high pressure liquid then flows to the receiver where it is stored until it is supplied to the cooling unit through the expansion valve. 4) Expansion- As the compressor withdraws the refrigerant vapour from the evaporator, the cooling unit must be supplied with low temperature, low pressure refrigerant capable of absorbing heat. This is done by a liquid control valve known as an expansion valve. This valve reduces the pressure of the high pressure liquid from the receiver to a low pressure liquid capable of absorbing heat. This also maintains a constant supply of liquid in the evaporator and act as a driving point between high and low pressure sides

• f the system.

Explain in detail Air Conditioner?

In electric circuit of an air conditioner when supply is connected to the thermostat switch at point a which in turns connects to the selector switch. The fan motor and compressor motor are in off position. When the selector switch knob is turned clockwise, the fan motors gets connected across the supply and the fan motor gets starts working. Normally, two speed selector switch is provided i.e. low and high.

Now if the thermostat switch is turned in ON position, the compressor motor starts running winding and auxiliary

• winding. The compressor motor is a capacitor start, capacitor

run type motor. When the normal speed is attained, the voltage relay trips and the auxiliary winding goes out of circuit whereas the running winding continues getting supply till the desired temperature in the room is attained. The thermal bulb

• f the thermostat switch makes or breaks the electric circuit

after sensing the room the temperature as per the setting position low cool or high cool. In this manner, the working of the compressor motor i.e. starting and stopping becomes

• automatic. In case the supply voltage falls down, the load on

the motor becomes more, the over load release comes into

• function. Thus the compressor motor gets disconnected from

the supply and becomes quite safe.

Explain in detail Water Cooler?

In electric circuit of water cooler there are two motors used. One for running compressor, is a capacitor start capacitor run induction motor. When the motor picks up the speed, the relay coil cuts off the starting winding (SW) along with the starting capacitor (Cs) and the motor continues to run on the running winding (RW) only.

There is a separate motor for the fan, which is used to cool the

• condenser. This is a capacitor start motor but capacitor is

not removed during running, also its operation is independent of the thermostat. The thermostat disconnects the motor from the supply when the water is cooled to the desired temperature. An O.L. (Over load) relay is also provided, which protects the motor from overloads.

What is electric traction? Give its advantages?

Electric traction: A system of running a vehicle by means of electrical energy is called traction. Advantages of Electric traction: 1) It is clean and pollution free system. 2) Better speed control and breaking. 3) Need less maintenance. 4) Less weight to horse power rating. 5) Less fire hazards. 6) Requirement of less terminal space. 7) Less wear and tear of track.

Define following

1) Scheduled speed- The ratio of distance covered between to stop and the total time of run including time to stop is called scheduled speed. 2) Pentagraph- Pentagraph is employed in electrical locomotives for collection of current from over head lines. It is mounted on the top of the vehicle and carriers a sliding shoe for contact with the over head wire. 3) EMU- It stands for electric multiple unit. It is an electric train in which each coach has its own prime mover and passengers. 4) Traction- The act of drawing or state of being drawn or propulsion of a vehicle is called traction.