Chapter 11 – Light, Shadows And Reflections

All objects around us cannot produce light. Let’s see how we can categorise items based on this.

• Luminous Objects: Objects that produce their own light are called luminous objects. E.g., the sun, fire, etc.
• Non-luminous Objects: Objects that cannot produce their own light are called non-luminous objects, e.g., wood, table, pencil, etc. But if you burn wood, that would result in a fire, an example of luminous objects.

It’s a basic property of light that any ray of light travels in a straight direction. It cannot be bent without applying any external force. Hence we get the angles of incidence equal to the angle of reflection in the reflection topic.

Transparent, Opaque, and Translucent Objects

We can have different types of objects that behave differently when encountered with the light source. Let’s see their types below:

• Opaque object: These objects block the light completely and cast a shadow. No light ray can pass through the solid object, and hence a dark shadow is formed—e.g., wall, brick etc.
• Transparent object: In this type of object, light can pass through the surface of the object. Almost all light passes through these materials, for example- air and water.
• Translucent object: In this type of object, some light passes through it, and some is blocked completely. This comes in between the transparent and opaque objects—for example, butter paper.

Reflection is a natural physics phenomenon in which the light bounces back from the reflecting surface and changes its direction.

When you drop the ball on the floor, it bounces back. Why doesn’t it pass through the ground? This is because the floor acts as a medium of change of momentum for the ball. In optics, we can say this medium acts as a reflecting surface.

Hence, whenever a ray of light strikes a reflecting surface, there is the direction’s reversion, although the intensity remains the same if there is no external force and pressure on the ray of light. The momentum is conserved when the directions are reversed. We have a property in reflection as follows:

• The angle of incidence = angle of reflection.
• All the three entities, namely the angle of incidence, the normal, and the reflection angle, lie on the same plane.

Lights and shadows are very interesting phenomena in physics. Apart from them, we even have a reflection and refraction phenomenon. In submarines, we can see the surface through a device called a periscope. It uses the dual reflection method to get the view of levels different from viewers. The spectacles that we wear also use the properties of refraction to show you clear and distinct images. We can even make a pinhole camera using light properties. There are a lot of widely used optical instruments that help us in our daily lives.

1.     What is the main difference between shadow and reflection?

Shadows are the projections of blocked lights on any surface. At the same time, reflections are the lights being reflected when hitting any surface and forming an image on the surface.

2.     What is the reflection for class 6th?

Reflection is a natural phenomenon where the light hits a reflecting surface and bounces back in proportion to the angle of incidence. When you stand in front of the mirror, your image is reflected, and hence you can see your beautiful face.

3.     What are the types of shadow?

The shadows can be divided into three parts based on the source of light. These are umbra, penumbra, and antumbra.

4.     Can we see a shadow even if there is light?

Shadows are formed in the presence of light. When the light is blocked from any object, then a shadow is cast. Hence we can see shadows in the presence of light. For example, in the daytime, you find the leaves’ shadows under the tree.

5.     Is a shadow a reflection?

No shadows are not a reflection as there are different ways the light is treated in both. In shadows, light is blocked, whereas, in reflection, the lights are bounced back.

6.     What exactly are shadows?

Shadows are dark shaped images formed on a surface when light is blocked from any solid object.