Properties and Image Formation by Plane Mirrors Explained
A plane mirror is a flat reflecting surface that forms images based on the principles of light reflection. When light from an object strikes a plane mirror, it reflects in such a way that the image appears to be behind the mirror. You observe your own image in a bathroom mirror due to this process. Plane mirrors are widely used in households, laboratories, and optical instruments because they form clear, undistorted images. Learn more about plane mirrors.
How Image Formation Occurs in Plane Mirrors
When light reflects off a plane mirror, the image appears at a location from which the reflected rays seem to diverge. In reality, the reflected light never actually passes through this point. This means the image is virtual—it cannot be caught on a screen. The image appears just as far behind the mirror's surface as the object is in front of it, creating a one-to-one correspondence in distance. Explore reflection in detail.
Key Characteristics of Images Formed by Plane Mirrors
- Images are virtual: The reflected rays appear to meet behind the mirror but do not actually converge there.
- The image is always upright (erect), matching the object's orientation vertically.
- Size of image equals size of object, ensuring magnification is 1.
- There is a left-right reversal, known as lateral inversion, so your right hand appears as left in the mirror.
- Image distance is equal to object distance from the mirror's surface.
Understanding Left-Right Reversal (Lateral Inversion)
One notable feature of a plane mirror is lateral inversion, where the image appears reversed from left to right. For example, if you raise your left hand, the image seems to raise its right hand. However, there is no top-bottom reversal—the image remains upright. This effect is based on perspective, and the reversal is different depending on your viewpoint.
Image and Object Distances
For any object placed in front of a plane mirror, the image forms at the same distance behind the mirror as the object is in front. If you are 2 meters from the mirror, your image appears to be 2 meters behind the mirror, making the total distance between you and your image 4 meters. This property is essential for constructing accurate ray diagrams in optics problems.
Relative Size of the Image
The size of the image created by a plane mirror is equal to the actual size of the object. Whether a person stands in front of the mirror or a small object is placed nearby, their images maintain the same dimensions. This results in a magnification value of 1 for all plane mirror images. More on mirror types here.
Step-by-Step Problem-Solving Approach
- Identify the position of the object in front of the mirror and measure its distance from the mirror.
- According to the law of reflection, the image distance is equal to the object distance but measured behind the mirror.
- Draw incident and reflected rays following the law: angle of incidence equals angle of reflection.
- Note that the image is virtual, upright, and laterally inverted compared to the object.
- Apply the magnification formula for plane mirrors: Magnification (M) = Image height / Object height = 1.
Key Formulas in Plane Mirror Problems
| Concept | Formula & Description |
|---|---|
| Image Distance (di) | di = do (distance behind mirror equals object distance in front) |
| Magnification (M) | M = Image height / Object height = 1 |
| Law of Reflection | Angle of incidence = Angle of reflection |
Example Problems
| Question | Solution |
|---|---|
| A person stands 1.5 meters in front of a plane mirror. What is the total distance between the person and their image? | Image forms 1.5 meters behind the mirror. Total distance = 1.5 m (object to mirror) + 1.5 m (mirror to image) = 3.0 meters. |
| An object is placed 10 cm from a plane mirror. Where is the image formed, and what are its properties? | Image forms 10 cm behind the mirror, is virtual, upright, and of the same size as the object. |
Summary Table: Properties of Plane Mirror Images
| Property | Plane Mirror Image |
|---|---|
| Nature | Virtual and upright |
| Position | Same distance behind mirror as object is in front |
| Size | Equal to object |
| Lateral Inversion | Yes (left-right reversal) |
For Deeper Understanding and Practice
- Strengthen your conceptual knowledge by exploring laws of reflection and reflection types.
- Test yourself with problems and ray diagram exercises on image formation in plane mirrors.
- Read further about applications at uses of plane mirrors.
- Advance to related optics topics at types of mirrors.
Mastering the principles behind images formed by plane mirrors is a fundamental skill for advanced optics and problem-solving. Continue learning with interactive sessions, practice worksheets, and expert-guided tutorials on Vedantu.
FAQs on Plane Mirrors in Physics: Concepts, Diagrams & Applications
1. What is a plane mirror?
A plane mirror is a flat, polished surface that reflects light to form images. It always produces an upright, virtual image of the same size as the object and exhibits lateral inversion, meaning left and right sides appear reversed.
2. What are the characteristics of the image formed by a plane mirror?
Images formed by a plane mirror have these properties:
• Always virtual and erect
• Same size as the object (magnification = 1)
• Image distance is equal to object distance from the mirror
• Exhibits lateral inversion
• Image cannot be projected onto a screen
3. What is lateral inversion in a plane mirror?
Lateral inversion refers to the apparent swapping of left and right sides in the image formed by a plane mirror. For example, if you raise your right hand, your image appears to raise its left hand.
4. State the laws of reflection for a plane mirror.
The two laws of reflection are:
1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, the reflected ray, and the normal to the point of incidence all lie in the same plane.
5. How do you draw a ray diagram for image formation in a plane mirror?
To draw a ray diagram for a plane mirror:
• Draw two rays from the top of the object striking the mirror at different points.
• Reflect both rays following the law of reflection (angle of incidence = angle of reflection).
• Extend the reflected rays backward using dotted lines; their intersection behind the mirror locates the image.
• The image is upright, virtual, and the same size as the object.
6. What is meant by virtual image?
A virtual image is formed at a location where light does not actually reach—it appears behind the mirror. Virtual images cannot be captured on a screen but can be seen by looking into the mirror. In plane mirrors, the image is always virtual and erect.
7. What is the formula for image distance in a plane mirror?
The image distance (di) is equal to the object distance (do) from the mirror’s surface:
di = do
This means if an object is 10 cm in front of a plane mirror, its image is formed 10 cm behind the mirror.
8. List some daily life uses of plane mirrors.
Plane mirrors are used in:
• Household mirrors (bathrooms, dressing tables)
• Periscopes and optical instruments
• Solar cookers for reflecting sunlight
• Vehicle rear-view mirrors
• Decoration and lighting setups
9. How is the size of the image formed by a plane mirror related to the object?
The size of the image in a plane mirror is always equal to the size of the object. The magnification produced is 1, so no enlargement or reduction occurs.
10. What is meant by left-right reversal in a plane mirror image?
Left-right reversal is another term for lateral inversion. It describes how the image in a plane mirror appears to swap left and right compared to the actual object, but keeps the top and bottom unchanged.
11. Can a real image be formed by a plane mirror? Explain.
No, a plane mirror always forms virtual images. The image appears to form behind the mirror where reflected light rays do not actually converge; hence, it cannot be projected onto a screen.
12. What is the required minimum height of a plane mirror to view your full image?
The minimum height of a plane mirror needed to view your full image is half your actual height. This is because light from your feet and head reflects to your eyes even if the mirror covers only half the vertical distance.
