. A text book of physics, for the use of students of science and engineering . mirror. o^»/i ^^>n» /_SCM=z_S CM. Hence SM = SM. and =, and therefore both these anglesare right angles. Stating this result in words we say that: the linejoining object and image is perpendicular to the mirror, and the image is asfar behind the mirror as the , object is in front of it. Expt. 117.—Reflection byplane mirror. Place a pieceof silvered glass mirror ver-tically upon a sheet ofdrawing paper, hi plan itis represented by AB inFig. 500. Fix a large pinvertically into the paper atS. On looking i
. A text book of physics, for the use of students of science and engineering . mirror. o^»/i ^^>n» /_SCM=z_S CM. Hence SM = SM. and =, and therefore both these anglesare right angles. Stating this result in words we say that: the linejoining object and image is perpendicular to the mirror, and the image is asfar behind the mirror as the , object is in front of it. Expt. 117.—Reflection byplane mirror. Place a pieceof silvered glass mirror ver-tically upon a sheet ofdrawing paper, hi plan itis represented by AB inFig. 500. Fix a large pinvertically into the paper atS. On looking into themirror an image of the pinwill he seen at S. The aim is to locate thisimage. Put another pin atC, and. looking horizontally with C and S in line, place a third pin at Din line with C and S. Repeat this procedure at E and F and at a numberof other positions. Draw the line AB. remove the mirror, and join the pointsin pairs, Forming the lines DC. FE, etc. These produced should all passthrough a single point S, the position of the image of S being thus found. /1 >. Fig. 500.—Experiment on reflection by plane mirror. XLIII IMAGE IN PLANE MIRROR 555 Now measure SM and SM, and show that they are equal. Again, GCDis a reflected ray corresponding to the incident ray SG. Draw the normalGK, and measure the angles SGK and KGD with a protractor. Do thesame for the other rays and make a table of the values of the angles ofincidence and reflection. It should be noted that if the mirror is a piece of thick plate glass, thereis a bending of the rays on entering and leaving the glass, as will be describedin Chapter XLV. This defect cannot be fully corrected, but by drawinga line parallel to AB at a distance of one third of the thickness of the glass,in front of the silvered surface, and making all measurements fromthis line instead of from the sil-vered surface, it will be found thatmuch more accurate results will beobtained.
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