In accordance with the discussion of the previous chapter that the mirror can be divided into three types, namely
flat mirror,
concave mirror and a
convex mirror, then this chapter will discuss the process of the formation of the shadow for each mirror.
The process of formation of a shadow on a flat mirror is quite simple. In accordance with the characteristics of a flat mirror that is a shadow formed is always virtual, upright , and equally large, then the distance to the mirror images forming the same distant object distance to the mirror and the shadow is behind the mirror. However, the reverse direction toward the object. To be more clear, look at the example III.1 image below:
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| Figure III.1 Examples of cases on a flat mirror |
Suppose the distance to the object and the mirror is 5 cm tall object is 6 cm, then the shadow distance to the mirror is 5 cm and the height is also equal to the shadow object is 6 c .
The process of formation of a concave mirror images using special assistance rays from a concave mirror. Shadow lies in the intersection point of two of the reflected light rays are privileged . As a case example, suppose the object is placed between the center of curvature ( M ) and the focal point of the mirror ( f ) as shown in the following figure III.2 .
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| Figure III.2 Examples of cases in a concave mirror |
Suppose is known distance focal point is 2 cm concave mirror , the object distance is 3 cm and 1 cm tall object is , the process of calculating the distance and height of the shadow is as follows :
1 ) DISTANCE OF SHADOWS ( Si )
1/So 1/Si + = 1 / f
( 1/3 ) + ( 1/Si ) = ( 1/2 )
1/Si = ( 1/2 ) - ( 1/3 )
Si = 6 cm
Thus , the shadow is 6 cm in front of the concave mirror ( real image )
2 ) Magnification SHADOWS ( M )
M = Si / So = -6 / 3 = -2
Thus , the shadow is 2 times magnification
( The image is enlarged )
3 ) HIGH SHADOW ( hi )
hi = M * ho = 2 * 1 = 2 cm
Thus , the shadow is 2 cm high
Images forming possess real ( true ) , inverted and magnified .
The process of formation of a convex mirror images also use the help of special rays of a convex mirror. Shadow lies in the intersection point of two of the reflected light rays are privileged. The main difference from a concave mirror and a convex mirror is the focal point of a concave mirror located in front of the mirror while the focal point of a convex mirror located behind the mirror. As a case example, suppose the objects placed in front of a convex mirror as shown in the following figure III.3 .
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| Figure III.3 Examples of cases in a convex mirror |
Suppose is known distance focal point is 2 cm convex mirror, the object distance is 3 cm and 1 cm tall object is , the process of calculating the distance and height of the shadow is as follows :
1 ) DISTANCE OF SHADOWS ( Si )
1/So 1/Si + = 1 / f
( 1/3 ) + ( 1/si ) = ( 1/-2 )
1/Si = ( 1/-2 ) - ( 1/3 )
Si = -1.5 cm
Thus , the shadow is located 1.5 cm behind the convex mirror ( virtual image )
2 ) Magnification SHADOWS ( M )
M = Si / So = -1.5 / 3 = 0.4
Thus , the shadow is 0.4 times magnification
( Shadow minimized )
3 ) HIGH SHADOW ( hi )
hi = M * ho = 0.4 * 1 = 0.4 cm
Thus , the shadow is 0.4 cm high
Images forming properties virtual, upright and reduced.
As for the lens is divided into two kinds , namely convex lens and a concave lens. The process of forming a shadow on the convex lens also uses special assistance rays of a convex lens. Lies in the shadow of two intersection points of light refracted ray is special. As a case example, suppose the objects placed in front of the convex lens as shown in the following figure III.4.
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| Figure III.4 Examples of cases in a convex lens |
Suppose is known distance focal point is 3 cm convex lens, the object distance is 5 cm and 1 cm tall object is, the process of calculating the distance and height of the shadow is as follows :
1 ) DISTANCE OF SHADOWS ( Si )
1/So 1/Si + = 1 / f
( 1/5 ) + ( 1/Si ) = ( 1/3 )
1/Si = ( 1/3 ) - ( 1/5 )
Si = 7.5 cm
Thus , the shadow is located 7.5 cm behind the lens Convex (real image)
2 ) Magnification SHADOWS (M)
M = -Si/So = -7.5 / 5 = -1.5
Thus , the shadow is 1.5 times magnification
(The image is enlarged)
3 ) HIGH SHADOW ( hi )
hi = M * ho = 1.5 * 1 = 1.5 cm
Thus , the shadow is 1.5 cm high
Images forming possess real ( true ) , inverted and magnified.
The process of forming a shadow on concave lens also uses special assistance rays from a concave lens. Lies in the shadow of two intersection points of light refracted ray is special. The main difference of concave lens and convex lens is the main focal point of a concave lens is located behind the main focal point of the lens while the convex lens located in front of the lens . As a case example, suppose the objects placed in front of a concave lens as shown in the following figure III.5 .
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| Figure III.5 Examples of cases on a concave lens |
Suppose is known distance focal point is 3 cm concave lens , the object distance is 5 cm and 1 cm tall object is , the process of calculating the distance and height of the shadow is as follows :
1 ) DISTANCE OF SHADOWS ( Si )
1/So 1/Si + = 1 / f
( 1/5 ) + ( 1/Si ) = ( 1/-3 )
1/Si = ( 1/-3 ) - ( 1/5 )
Si = -1.88 cm
Thus , the shadow is 1.88 cm in front of the concave lens ( virtual image )
2 ) Magnification SHADOWS ( M )
M = -Si/So = - (-1.88) / 5 = 0.38
Thus , the shadow is 0:38 times magnification
( Shadow minimized )
3 ) HIGH SHADOW ( hi )
hi = M * ho = 0.38 * 1 = 0.38 cm
Thus , the shadow is 0:38 cm high
Images forming properties virtual , upright and reduced .
