INTERFERENCE When two wave trains of the same frequency amp the same amplitude traveling in the same direction are superimposed on one another they produce interference If at any point the waves are in phase there is an increase in resultant amplitude ie ID: 599602
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PRINCIPLE OF OPTICAL MEASURING INSTRUMENTS
INTERFERENCE:When two wave trains of the same frequency & the same amplitude traveling in the same direction are superimposed on one another they produce interferenceIf at any point the waves are in phase, there is an increase in resultant amplitude, i.e. a constructive interference.If the waves are out of phase & there is decrease in the resultant amplitude, i.e. destructive interference
18/2/2012
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lec# 13 & 14Slide2
PRINCIPLE OF OPTICAL MEASURING INSTRUMENTS
2. CONDITIONS FOR INTERFERENCE OF LIGHT WAVES:The two sources should continuously emit waves of the same wave length or frequencyFor obtaining interference fringes, the amplitude of the two interfering wave trains should equal or very nearly equalThe two sets of wave-trains from the two sources should either have the same phase or a constant in difference in phaseThe two sources should be very narrow
18/2/2012
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lec# 13 & 14Slide3
PRINCIPLE OF OPTICAL MEASURING INSTRUMENTS
3. MONOCHROMATIC BEAM OF LIGHT:A Monochromatic beam of light gives light of only one wave length or one color.It is difficult to get a truly monochromatic source of light. However by using light filters it is possible to get a source that gives light within a narrow bend of wave lengths ±5x10-10mLight emitted by certain elements eg. Mercury, sodium & cadmium is suitable.
In metrology this light is usually obtained from an electrical discharge lamp
18/2/2012
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lec# 13 & 14Slide4
PRINCIPLE OF OPTICAL MEASURING INSTRUMENTS
Depending upon the optical setup, the interference bands can appear as parallel bands, or as concentric circlesThe interference phenomenon can be used to make the measurement of high precision by utilizing the fact that the path difference b/w two dark bands or two light bands is one wave length18/2/20124
lec# 13 & 14Slide5
PRACTICAL # 03
Object: To learn different uses of Combination setApparatus: Combination set with 300mmblade, square head & centre head, sections for angle measurementProcedure: As DemonstratedLearning Outcome: After performing measurements with combination set we feel confidence to make its application independently
18/2/2012
lec# 13 & 14
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PRACTICAL # 03
Combination Sets can be used as:Outside try squareInside try squareMitre SquareSprit level45 levelPlumb levelDepth gaugeHeight gaugeMarking gaugeCentre head use
Protractor use
18/2/2012lec# 13 & 14
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