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 our 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 of 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 on 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 of 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 other 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 of 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 or ornamentation. The article is made cathode, the metal is deposited is made anode and electrolyte is the salt solution of 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 order to make it conducting. The mould is dipped in an electroforming cell as a cathode.
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