Reflection of Light – Class 7
Subjective Questions
1. Write any two uses of plane mirrors.
- Used as looking glasses.
- Used in periscopes and solar cookers.
- Used in periscopes and solar cookers.
2. How is a spherical mirror different from a plane mirror?
- Plane mirror has a flat reflecting surface.
Images formed in same size .
- Spherical mirror has a curved reflecting surface (concave/convex).
- Images formed differ in size and type.
- Spherical mirror has a curved reflecting surface (concave/convex).
- Images formed differ in size and type.
3. Define the following terms:
a) Regular reflection → Reflection from a smooth surface.
b) Diffused reflection → Reflection from a rough surface.
c) Primary colours → Red, Blue, Green.
d) Secondary colours → Orange, Violet, Green (formed by mixing two primary colours).
e) Lateral inversion → Left-right reversal of an image in a mirror.
b) Diffused reflection → Reflection from a rough surface.
c) Primary colours → Red, Blue, Green.
d) Secondary colours → Orange, Violet, Green (formed by mixing two primary colours).
e) Lateral inversion → Left-right reversal of an image in a mirror.
4. State the laws of reflection. How will you verify it experimentally?
Laws of Reflection:
1. Angle of incidence = Angle of reflection.
2. Incident ray, reflected ray, and normal lie in the same plane.
Verification: Using a plane mirror, protractor, and laser light to measure angles.
1. Angle of incidence = Angle of reflection.
2. Incident ray, reflected ray, and normal lie in the same plane.
Verification: Using a plane mirror, protractor, and laser light to measure angles.
5. What are the characteristics of the image formed by a plane mirror?
- Erect
- Virtual
- Same size as object
- Laterally inverted
- Same distance behind mirror as object is in front
- Virtual
- Same size as object
- Laterally inverted
- Same distance behind mirror as object is in front
Exemplar Problems
1. Except for one colour, an object absorbs all the other colours of sunlight. If this colour is mixed with blue, then it turns green. What is the colour of the object?
The object is Yellow (Yellow + Blue = Green).
2. Write "AMBULANCE" and observe it in the plane mirror. What is the difference in the text written by you and its image?
In the mirror, the word appears laterally inverted (reversed left to right)
" AMBULANCE" is ECNALUBMA.
That is why "AMBULANCE" is written in reverse on vehicles.
3. Suppose a person of height 6 feet is standing 2 m away from the plane mirror. What is the distance between him and his image? What will be the height of his image?
Distance between person and image = 2 m + 2 m = 4 m.
Height of image = 6 feet (same as object).
Height of image = 6 feet (same as object).
