VISN1111-Tut5-2013
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VISN1111 (2013) VIS N1 111 Geometr ical and Physical Optic s 20 13 Tutorial-4 1. What will be the rotation of a plane mirror reflecting a spot of li ght onto a straight scale (a tangent scale) 1 m from t he mirror if th e s pot of light moves through 5 cm? Ans. 1.43 ° 2. A sight-testing chart measuring 1.2 m × 0.8 m, the longer dimension being vertical, is to be viewed by reflection in a plane mirror. Find the smallest size of mirror that can be used if the chart is 3.25 m and the observer 2.75 m f rom the mirror. If the observer’s eye is 1.2 m and the lower edge of the chart 1.5 m. above the ground, wha t must be the height of the bottom edge of the mirror? Ans. 0.55 m × 0.367 m; 1.3375 m. above the ground. 3. An object is held against a plate glass mirror of refractive index 1.54. Its image appears to be 10 mm in from the surface. What is the thickness of the mirror? Ans. 7.7 mm 4. A concave mirror has a radius of 12 cm. a) What is the power of the mirror? b) A small object is sit uated on axis 5 cm from the mirror. What is the vergence of ray s originating at the object before reflection from the mirror? c) Describe the final image. Ans. a) 16.67 D, b) – 20 D, c) 30 cm t o the righ t of the mirror , virtual, erect, 6 X 5. Determine the ratio of focal lengths for two identical, thin plano-convex lenses when one is silvered on its flat side and the other on its curved side. Light is incident on the unsilve red side. Ans. n/(n-1). 6. A real inverted image twice the size of the object is produced 20 cm from a mirror. Find the radius of curvature of the mirror. What is the object’s position when the magnification is four and the image is erect? Ans. r = −13 1 / 3 cm. l = − 5 cm. 7. A concave spherical mirror of radius 200 cm, converges light from a distant object onto a concave mirror of radius 120 cm. The latter is 40 cm in f ront of the former. The light comes to a focus and is made parallel by a thin +10 D lens. Where should this lens be placed? The system is as sh own in the figu re below. Ans. T he lens must be placed i n the hole in the first mirror. 8. A concave and a convex mirror each of 40 cm radius of curvature are placed opposite to each other and 50 cm apart on a common axis. An object 2 cm high is placed midway between them. Find the position and size of the image formed, both by calculation and by ray tracing, when light is reflected first at the convex then at the concave mirror. Ans. 29.73cm to the right of the concave mirror; the size of the image is -0.43cm
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VISN1111 (2013)
VISN1111 Geometrical and Physical Optics 2013
Tutorial-4
1. What will be the rotation of a plane mirror reflecting a spot of light onto a straight scale (a tangentscale) 1 m from the mirror if the spot of light moves through 5 cm? Ans. 1.43°
2. A sight-testing chart measuring 1.2 m × 0.8 m, the longer dimension being vertical, is to be
viewed by reflection in a plane mirror. Find the smallest size of mirror that can be used if thechart is 3.25 m and the observer 2.75 m from the mirror. If the observer’s eye is 1.2 m and the
lower edge of the chart 1.5 m. above the ground, what must be the height of the bottom edge of
the mirror? Ans. 0.55 m × 0.367 m; 1.3375 m. above the ground.
3. An object is held against a plate glass mirror of refractive index 1.54. Its image appears to be 10mm in from the surface. What is the thickness of the mirror? Ans. 7.7 mm
4. A concave mirror has a radius of 12 cm.a) What is the power of the mirror?
b) A small object is situated on axis 5 cm from the mirror. What is the vergence of rays
originating at the object before reflection from the mirror?
c) Describe the final image.
Ans. a) 16.67 D, b) –20 D, c) 30 cm to the right of the mirror, virtual, erect, 6 X
5. Determine the ratio of focal lengths for two identical, thin plano-convex lenses when one is
silvered on its flat side and the other on its curved side. Light is incident on the unsilvered side.Ans. n/(n-1).
6. A real inverted image twice the size of the object is produced 20 cm from a mirror. Find the radius
of curvature of the mirror. What is the object’s position when the magnification is four and theimage is erect? Ans. r = −131
/3 cm. l = − 5 cm.
7. A concave spherical mirror of radius 200 cm, converges light from a distant object onto a
concave mirror of radius 120 cm. The latter is 40 cm in front of the former. The light comes to a
focus and is made parallel by a thin +10 D lens. Where should this lens be placed? The system is
as shown in the figure below. Ans. The lens must be placed in the hole in the first mirror.
8. A concave and a convex mirror each of 40 cm radius of curvature are placed opposite to each
other and 50 cm apart on a common axis. An object 2 cm high is placed midway between them.
Find the position and size of the image formed, both by calculation and by ray tracing, when
light is reflected first at the convex then at the concave mirror.
Ans. 29.73cm to the right of the concave mirror; the size of the image is -0.43cm
