CBSE Class 6 Science Revision Notes Chapter 11

CBSE Class 6 Science Chapter 11 Revision Notes – Light, Shadows And Reflections

Class 6 Science Chapter 11 Notes expose students to the concepts related to light, its reflection, and the shadows formed by it. This is an important chapter in Class 6 Science from the point of view of exams. So, students must have a fair understanding of the topic to perform better in the exams.

At Extramarks, subject matter experts prepare the notes as per the CBSE guidelines. As these notes cover all of the major concepts, students can revise the entire chapter effectively by reviewing these notes. These notes are easily accessible on the website. Students can boost their exam preparations with these quality revision notes.

Revision Notes for CBSE Class 6 Science Chapter 11

Access Class 6 Science Chapter 11 – Light, Shadows And Reflection Notes

Definition of Light

• Light is a form of energy that enables every living being to see the objects around them.
• When it falls on dust particles in the atmosphere, it causes a sensation in the eyes due to its scattering effect. This sensation is called sight or vision.
• Objects become visible when light stimulates vision in the eyes.
• Without light, nothing is visible. But without proper vision, nothing can be seen. So, light and vision are both required to see objects.

Sources of Light

• A source of light can be anything. Light is emitted from the sun, and other stars, as well as from a bulb. While celestial bodies themselves emit light, humans have invented light bulbs. So, based on the nature of their sources, light can be divided into two categories: natural sources and artificial sources.
• Natural sources of light are those objects that have their own light. For example, the sun, the stars in the galaxies, the flame of a candle, etc.
• Artificial sources are those objects that cannot emit light without the intervention of human beings. For example, tube lights, bulbs, torches, etc.

Optical Media and its Types

• Optical media is a medium through which light travels from one place to another.
• However, every object does not allow light to travel through it.
• Objects that let light pass through without any hindrance are called transparent objects. 
• Objects that do not let light pass through them are called opaque objects. 
• Objects that allow the light to pass through but only partially are called translucent objects.
• Water, glass, air, etc., are transparent objects.
• Metal, pencils, rubber balls, etc., are examples of opaque objects.
• Translucent objects can be best described by the examples of butter paper, chiselled glass, etc.

Definition of Shadow

• Light travels in a straight line. If its path is obstructed by any object, light cannot reach its destination. The dark region formed because of the absence of light in that region is called a shadow.
• A shadow, therefore, cannot be formed without a source of light.
• Opaque and translucent objects obstruct the path of light. So, they form shadows.
• Transparent objects cannot cast shadows as light passes through them, even if they obstruct it.

Properties of a Shadow

• Properties depending on the size of the light source:

• If the size of light sources is extremely small or so small that it looks like a point, light emitted from such sources can form only one shadow. This dark shadow is called the umbra. 
• When the area of the light source is large, the light emitted from it creates two dark regions. One region at the centre, and another at the direction of propagation of light. 

• The dark shadow at the centre is called umbra.
• The lighter, darker shadow is known as the penumbra.

• The size of these shadowed zones depends on the distance between the screen on which the shadow is formed and the object that causes the shadow to be formed.
• The size of the umbra decreases if the distance between the screen and the object increases, and vice versa.

• The colour of the shadow does not depend on the colour of the object. Shadows have only one colour, and that is black.
• The length of the shadow depends on the angle of the incident light on an object. It is observed that the length of a person’s shadow becomes shorter as the sun starts going overhead. 

Eclipse

• An eclipse is an astronomical phenomenon.
• When a shadow is created by the heavenly bodies in space, it is called an eclipse.
• During an eclipse, the sun and moon cannot be seen in the sky for quite some time.
• Solar Eclipse: When the sun, the moon, and the earth come in a straight line, the light from the sun cannot reach the earth due to the obstruction by the moon.This casts a shadow on earth, and the sun becomes invisible during the day. This phenomenon is called a solar eclipse.
• Lunar Eclipse: A lunar eclipse happens when the moon becomes invisible. When the earth comes between the sun and the moon, it creates a shadow on the moon and makes it invisible from the night sky.

Definition of Reflection of Light

• When a light ray falls on a surface, some of it bounces back. This event is called reflection.
• Objects are visible because light reflects from them and stimulates sight in the eyes.
• Because of the reflection, we can see our images in the mirror.