13.2.3. Activity 13.3

A source of light O is placed in front of a plane mirror PQ. Two rays OA and OC are incident on it (Fig. 13.5). Can you find out the direction of the reflected rays?

In this activity, we place a light source (O) in front of a plane mirror (PQ). Two rays of light (OA and OC) come from the source and reach different points on the mirror. We are tasked with figuring out how these rays will reflect off the surface of the mirror. This helps understand how the light interacts with reflective surfaces.

Imagine shining a flashlight at a flat mirror. The light beam hits the mirror and bounces away, just like how a ball would bounce off a wall. The angle at which the light hits the mirror is just as important as the angle it leaves, which is what we will explore in this activity.

Draw normals to the surface of the mirror PQ, at the points A and C. Then draw the reflected rays at the points A and C. How would you draw these rays? Call the reflected rays AB and CD, respectively.

In this step, after identifying where the light rays hit the mirror, we need to draw 'normals,' which are perpendicular lines from the points on the mirror where the light rays strike. From these points (A and C), we can draw the reflected rays (AB and CD) based on the angle of incidence. This helps illustrate how light behaves upon striking a reflective surface, emphasizing the relationship between the angle of incidence and the angle of reflection.

Think of throwing a basketball towards a hoop. The angle at which you throw the ball (angle of incidence) determines where it will bounce off the backboard (angle of reflection). Just like this basketball example, light rays follow predictable paths when they hit a mirror.

Extend them further. Do they meet? Extend them backwards. Do they meet now? If they meet, mark this point as I.

Here, we extend the reflected rays AB and CD to see if they intersect at any point. In reality, the rays won't physically meet, but they appear to come from a common point (I) when viewed from a specific angle. This illustrates the idea that while the rays reflect, they create what is known as a virtual image that seems to come from point I.

Think about how when you look at a tree in the distance, the tree appears to rise from the ground 'beyond' where the ground meets the tree trunk—that’s the concept of a virtual image. You perceive it as if it’s coming from a point in space where the extended lines seem to converge, even though it exists farther away.

For a viewer’s eye at E (Fig. 13.5), do the reflected rays appear to come from the point I. Since the reflected rays do not actually meet at I, but only appear to do so, we say that a virtual image of the point O is formed at I.

As we look at the reflection in the mirror from point E, the light rays seem to originate from point I—this is the virtual image location. A virtual image is one that cannot be projected onto a screen because the light rays don't actually converge; they only seem to. This leads to the concept of lateral inversion, where the image appears reversed left to right.

If you stand in front of a mirror and raise your right hand, the image of your hand appears to be the left hand in the mirror. This is lateral inversion. It’s the same principle that helps us understand more complex reflections, like seeing your face in a compact mirror versus a full-size mirror.

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