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Light Energy - Lateral Inversion

Grade 7ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Lateral Inversion is the phenomenon where the left side of an object appears as the right side of its image in a plane mirror, and vice versa.

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The image formed by a plane mirror is always virtual (cannot be caught on a screen) and erect (upright).

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The distance of the object from the mirror, denoted as uu, is equal to the distance of the image from the mirror, denoted as vv. This is expressed as u=vu = v.

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The size of the image is exactly equal to the size of the object, meaning the height of the object hoh_o equals the height of the image hih_i.

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Symmetry: Letters that have vertical symmetry, such as A,H,I,M,O,T,U,V,W,X,YA, H, I, M, O, T, U, V, W, X, Y, do not appear changed by lateral inversion.

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Practical Application: The word 'AMBULANCE' is written in reverse (ECNALUBMA\text{ECNALUBMA}) on the front of emergency vehicles so that drivers in front see the word correctly in their rear-view mirrors due to lateral inversion.

📐Formulae

u=vu = v

ho=hih_o = h_i

Distance between object and image=u+v=2u\text{Distance between object and image} = u + v = 2u

💡Examples

Problem 1:

A boy stands 4 m4\text{ m} away from a large plane mirror. How far is his image from him?

Solution:

8 m8\text{ m}

Explanation:

According to the properties of a plane mirror, object distance u=4 mu = 4\text{ m} is equal to image distance v=4 mv = 4\text{ m}. The total distance between the boy and his image is u+v=4 m+4 m=8 mu + v = 4\text{ m} + 4\text{ m} = 8\text{ m}.

Problem 2:

If the letter BB is placed in front of a mirror, describe its image.

Solution:

The image of BB will be laterally inverted (facing the opposite direction).

Explanation:

Because the letter BB is not vertically symmetrical, lateral inversion will cause the curved parts of the 'B' that face right to appear as if they are facing left in the mirror image.

Problem 3:

A person moves 1 m1\text{ m} closer to a mirror from an initial distance of 5 m5\text{ m}. What is the new distance between the person and the image?

Solution:

8 m8\text{ m}

Explanation:

The initial distance was 5 m5\text{ m}. After moving 1 m1\text{ m} closer, the new object distance u=5 m−1 m=4 mu = 5\text{ m} - 1\text{ m} = 4\text{ m}. Since u=vu = v, the image distance is also 4 m4\text{ m}. The total distance is u+v=4 m+4 m=8 mu + v = 4\text{ m} + 4\text{ m} = 8\text{ m}.

Lateral Inversion - Revision Notes & Key Formulas | ICSE Class 7 Science