AB = 60 - 50 = 10 cm. from EXERCISE-7 (A) IMAGE B' What do you mean Slate mirror the back silvered surface. ected light (a) plane mirror, 6. State the two laws of reflection of light. 7. State the laws of reflection and describe an experiment to verify them. 8. A light ray is incident normally on a plane mirror. (a) What is its angle of incidence ? (b) What is the direction of reflected ray ? Show it on a diagram Ans. (a) 0°, (b) same as incident ray 9. Draw a diagram to show the reflection of a ray of light by a plane mirror. In the diagram, label the incident ray, the reflected ray, the normal, the angle of incidence and the angle of reflection. 10. Fig. 7.15 shows an incident ray AO and the normal ON on a plane mirror. The angle which the incident by reflection of light? which surface of a plane mirror reflects most of the light incident on it : the front smooth surface or Ans. Back silvered surface. 1 Explain the following terms: (b) incident ray, (c) reflected ray, (d) angle of incidence, and le) angle of reflection, Draw diagram/diagrams to show them. With the help of diagrams, explain the difference between regular and irregular reflection. Differentiate between reflection of light from a plane mirror and that from a plane sheet of paper. surface ed light eflected image State 153
Answers
( Q. 7 diagram )
Q. 8 ( b ) - diagram
( Q. 9 diagram )
( Q. 10 diagram )
( Q. 11 diagram )
Answer:
Q. 6 Answer :
Laws of reflection are:
(i) The incident ray, the reflected ray and the normal ray at the point of incidence, lie in the same plane.
(ii) The angle of incidence is equal to the angle of reflection.
Q. 7 Answer :
Laws of reflection
(i) The incident ray, the reflected ray and the normal at the point of incidence, lie in the same plane.
(ii) The angle of incidence and angle of reflection are equal i.e. ∠i = ∠r.
Verification
Take a wooden drawing board and fix a white sheet of paper on it. In the middle of paper draw a straight line KK\ Mark a point B on it. Draw a perpendicular BN. Place a mirror XX’ on line KK’ such that polished side of mirror is along the line. Hold-the mirror in the mirror holder.
Fix two steel pins P and Q on the straight line AB at least 10 cm apart. Look for the images of the pins P and Q and fix two pins P Q’ such that P’, Q’ and images of P and Q are all in the same straight line. Remove the pins and draw small circles around the pin pricks.
Remove the mirror also. Join P’Q’ and produce the straight line to meet at B.
Measure ∠ABN = i and ∠CBN = r.
It is found that ∠i = ∠r. This proves that Angle of Incidence is equal to Angle of Reflection.
As the incident ray, the reflected ray and the normal lie in the plane of paper, therefore, they lie in the same plane.
Q.8 ( a ) Answer :
Angle of incidence is 0°. As angle of incidence is the angle between incident ray and normal.
Q.8 ( b )
The direction of the reflected ray is opposite to the direction of the incident ray.
Q. 10 ( a ) Answer :
Angle of incidence = 90° -30° = 60°
Q. 10 ( b )
Angle between the incident ray and reflected ray = Angle of incidence + Angle of reflection
Angle of reflection = Angle of incidence
= 60°
Therefore, Angle between the incident ray and reflected ray = 60° + 60° = 120⁰
Q. 11 Answer :
Incident ray - the ray of light falling on the surface AB is called the incident ray.
Reflected ray - the incident ray bouncing back in the same medium after striking the reflecting surface is called reflected ray.
Angle of incidence - the angle form between the incident ray and the normal is the angle of incidence.
Angle of reflection - the angle formed between the normal and the reflected ray is called angle of reflection.
explain the difference between regular and irregular reflection
answer :
Difference between regular and irregular reflection is as follows-
(1). If all the parallel rays which are reflected from a plane surface are not parallel then that reflection of incident rays is known as irregular reflection.
If all the parallel rays which are reflected from a plane surface are parallel then that reflection of incident rays is known as regular reflection.
(2). Reflection from smooth highly polished surface for example mirror, surface of silver gives regular reflection.
Reflection from a rough and uneven surface for example wood, leaf of tree, piece of paper etc gives irregular reflection.
(3). In regular reflection, light reflected from a smooth surface in a definite direction.
In irregular reflection, light reflected from a rough surface in all directions and not in a definite direction.
Differentiate between reflection of light from a plane mirror and that from a plane sheet of paper.
answer :
Reflection of light from a plane mirror 1) it is a regular reflection 2)light rays falls on a smooth and polished surface,a parallel beam of light is incident on a plane mirror,the reflected beam is also parallel.
Reflection of light from a sheet of paper 1) its a irregular reflection 2) light rays strike at different parts of a rough surface,each rays gets reflected from different points of rough surface in different direction.
Answer:
=>>is a convenient practice. The practical reason is, the back coated mirror is easy to handle. The coating is not disturbed while handling a mirror. It is protected by the front, which is not coated. Technically, a back coated mirror produces two reflections, one from the front which is not coated. This ref lo section is a weak reflection. The reflection from the coated side is stronger. A normal back coated mirror this produced two images. The image from the coated side dominates. Some optical instruments such as a DSLR camera, has a mirror inside, just behind the lens. This mirror is a front coated mirror which avoids double images. Being front coated, we are not supposed to touch it.