Class 7 Science - TAMILNADU
Light: Shadows and Reflections
The chapter 'Light: Shadows and Reflections' in Class 7 Science from Tamil Nadu Samacheer Kalvi explores the fascinating properties of light. Students learn how light travels in a straight line, how shadows are formed when an opaque object blocks this path, and how mirrors change the direction of light through reflection. Understanding these concepts helps explain everyday optical phenomena like why we cannot see through wood, why shadows change size throughout the day, and how image formation works in plane mirrors. This chapter is fundamental for scoring well in both objective and descriptive board exam questions.
Start Learning FreeKey Concepts
Luminous and Non-Luminous Objects
Objects that emit their own light are called luminous objects (e.g., the Sun, a torch), while objects that do not emit light of their own but reflect light from other sources are non-luminous objects (e.g., the Moon, a chair).
Transparent, Translucent, and Opaque Objects
Transparent objects allow light to pass through them completely, translucent objects allow light to pass through partially, and opaque objects do not allow light to pass through them at all.
Rectilinear Propagation of Light
Light always travels in a straight line path in a given medium, a property known as the rectilinear propagation of light.
Shadow Formation
Shadows are dark patches formed when an opaque object comes in the path of light, requiring a source of light, an opaque object, and a screen.
Reflection of Light
The bouncing back of light rays from a polished or shiny surface, such as a plane mirror, is called reflection, which enables us to see images.
Important Formulas
Board Exam Info
In Tamil Nadu Samacheer Kalvi Class 7 Science exams, this chapter typically carries around 6 to 8 marks. Questions frequently include fill-in-the-blanks, true or false, definition-based short answers, drawing ray diagrams for shadows, and distinguishing between transparent, translucent, and opaque objects.
Frequently Asked Questions
Why is a shadow always black, even if the object is colorful?
A shadow is formed simply by the absence of light where an opaque object blocks it. Since no light reaches the screen from that blocked region, it appears dark or black regardless of the object's actual color.
Can we see a shadow in total darkness?
No, a shadow cannot be formed or seen in total darkness because a light source is essential to create the contrast between the illuminated area and the blocked path.
What is lateral inversion in a plane mirror?
Lateral inversion is the phenomenon where the right side of an object appears as the left side in its mirror image, and vice versa.
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