NCERT Class 7 Science Chapter 11
Light, Shadows and Reflections
This chapter explores the properties of light, the formation of shadows, and the laws of reflection for CBSE Class 7 students. Students learn about transparent, translucent, and opaque objects, how shadows are formed, and how light reflects from flat and curved mirrors. Practical activities involving mirrors and light sources help students visualise the concepts of image formation and reflection.
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Key Terms
- Reflection of Light
- The bouncing back of light rays when they strike a smooth, shiny surface such as a mirror. It follows two laws: the angle of incidence equals the angle of reflection, and the incident ray, reflected ray, and normal all lie in the same plane.
- Transparent Object
- An object that allows light to pass through it completely, enabling objects to be seen clearly on the other side. Examples include clear glass and clean water.
- Opaque Object
- An object that does not allow light to pass through it, blocking light completely and forming a shadow. Examples include wood, metal, and stone.
- Translucent Object
- An object that allows only some light to pass through it, making objects on the other side appear blurry. Examples include frosted glass and butter paper.
- Shadow
- A dark area formed on a surface when an opaque object blocks the path of light coming from a source.
- Plane Mirror
- A flat, smooth mirror that produces a virtual, erect, and laterally inverted image of the same size as the object.
Frequently Asked Questions
What are the laws of reflection of light?▾
The two laws of reflection are: (1) The angle of incidence is always equal to the angle of reflection, measured from the normal to the surface at the point of incidence. (2) The incident ray, the reflected ray, and the normal at the point of incidence all lie in the same plane.
What is the difference between transparent, translucent, and opaque objects?▾
Transparent objects allow light to pass through completely (clear glass), so you can see through them clearly. Translucent objects allow partial light through (frosted glass), making things appear blurry. Opaque objects block all light (metal, wood), forming shadows.
How is a shadow formed?▾
A shadow is formed when an opaque object comes between a light source and a surface. The object blocks the light, creating a dark region (shadow) on the surface behind it. The size and shape of the shadow depend on the position and size of the light source.
What are the properties of an image formed by a plane mirror?▾
An image formed by a plane mirror is virtual (cannot be obtained on a screen), erect (right side up), the same size as the object, and laterally inverted (left and right are reversed). The image appears to be as far behind the mirror as the object is in front.
What is lateral inversion in mirrors?▾
Lateral inversion is the phenomenon where the left side of an object appears as the right side in a mirror image and vice versa. For example, the letter 'b' appears as 'd' in a plane mirror. This is why writing appears reversed when seen in a mirror.
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