What is the difference between real and virtual images?

A real image is formed when light rays actually converge at a point after reflection (or refraction). These images can be projected onto a screen. They are typically formed in front of a concave mirror (or behind a convex lens) and are usually inverted. A virtual image, on the other hand, is formed when light rays only appear to diverge from a point after reflection (or refraction). These images cannot be projected onto a screen. They are typically formed behind a plane mirror or convex mirror (or in front of a concave lens) and are always erect.

Why does a plane mirror cause lateral inversion?

Lateral inversion is the phenomenon where the left side of an object appears as the right side of its image, and vice-versa, in a plane mirror. This occurs because reflection reverses the direction of light perpendicular to the mirror surface, but not parallel to it. When you face a mirror, your left hand is closer to the mirror's left edge, and its reflection appears on the image's right side, maintaining the same distance from the mirror's left edge. The mirror effectively flips the image along a vertical axis, leading to this left-right reversal.

How does diffuse reflection help us see objects?

Diffuse reflection is crucial for our ability to see most objects around us that do not emit their own light. When light strikes a rough surface, it reflects in many different directions. This scattering of light means that some reflected rays reach our eyes regardless of our viewing angle. If all objects only exhibited specular reflection, we would only see clear images of light sources and mirrors, and other objects would appear dark unless we were in a very specific position to catch a reflected ray.

Can a convex mirror form a real image?

No, a convex mirror can never form a real image for a real object. Convex mirrors are diverging mirrors; they always spread out incident parallel rays of light. Consequently, the reflected rays never actually converge in front of the mirror. Instead, they appear to diverge from a point behind the mirror, which is its principal focus. Therefore, a convex mirror always forms a virtual, erect, and diminished image for any real object placed in front of it.

What is the significance of the normal in the laws of reflection?

The normal is an imaginary line drawn perpendicular to the reflecting surface at the point where the incident ray strikes it. Its significance is paramount because both the angle of incidence and the angle of reflection are defined and measured with respect to this normal, not the surface itself. This consistent reference line ensures that the laws of reflection hold true for any angle of incidence and for both plane and curved surfaces, simplifying the analysis of light paths.

How does the number of images change when two plane mirrors are inclined at different angles?

The number of images formed by two plane mirrors inclined at an angle $ heta$ depends on the value of $rac{360^circ}{ heta}$. If this ratio is an even integer, the number of images is $n = rac{360^circ}{ heta} - 1$. If it's an odd integer, $n = rac{360^circ}{ heta} - 1$ if the object is placed symmetrically, and $n = rac{360^circ}{ heta}$ if placed asymmetrically. If the ratio is a fraction, the number of images is $n = ext{floor}left(rac{360^circ}{ heta} ight)$. As the angle $ heta$ decreases, the number of images increases, approaching infinity when $ heta = 0^circ$ (parallel mirrors).

Reflection of Light

Physics

NEET UG

Version 1Updated 22 Mar 2026

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Reflection of light is a fundamental phenomenon where light rays, upon striking a surface, return into the same medium. This interaction is governed by two primary laws: first, the angle of incidence is equal to the angle of reflection; and second, the incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane. This principle is crucial for u…

Quick Summary

Reflection of light is the bouncing back of light into the same medium after striking a surface. It's governed by two fundamental laws: the angle of incidence equals the angle of reflection ( $heta_i = \theta_r$ ), and the incident ray, reflected ray, and normal all lie in the same plane.

Reflection can be specular (from smooth surfaces, forming clear images) or diffuse (from rough surfaces, scattering light and making objects visible from all angles). Plane mirrors form virtual, erect, laterally inverted images of the same size and at the same distance behind the mirror as the object is in front.

Spherical mirrors are curved: concave mirrors are converging, while convex mirrors are diverging. Key terms for spherical mirrors include pole (P), center of curvature (C), radius of curvature (R), principal axis, principal focus (F), and focal length (f).

The mirror formula, $rac{1}{f} = \frac{1}{v} + \frac{1}{u}$ , relates object distance ( $u$ ), image distance ( $v$ ), and focal length ( $f$ ), while linear magnification ( $m = h_i/h_o = -v/u$ ) describes image size and orientation.

Strict adherence to the New Cartesian Sign Convention is crucial for accurate calculations.

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Key Concepts

Image Formation by a Plane Mirror

A plane mirror always forms a virtual, erect, and laterally inverted image. The image is located as far…

New Cartesian Sign Convention for Spherical Mirrors

This convention is crucial for applying the mirror formula correctly. The pole of the mirror is the origin.…

Relationship between Focal Length and Radius of Curvature

For spherical mirrors, the focal length ( $f$ ) is half of the radius of curvature ( $R$ ). This relationship, $f…

Laws of Reflection:

* $\theta_i = \theta_r$ * Incident ray, reflected ray, normal are coplanar.

Plane Mirror: — Virtual, erect, laterally inverted, same size,

u = |v|

Mirror Rotation (fixed incident ray): — Reflected ray rotates by

2\theta

Number of Images (two mirrors at $\theta$): —

n = \frac{360^\circ}{\theta} - 1

(if even or symmetric odd),

n = \frac{360^\circ}{\theta}

(if asymmetric odd),

n = \text{floor}(\frac{360^\circ}{\theta})

(if fraction).

Spherical Mirrors: — Concave (converging,

f<0

), Convex (diverging,

f>0

Focal Length: —

f = R/2

Mirror Formula: —

\frac{1}{f} = \frac{1}{v} + \frac{1}{u}

(with New Cartesian Sign Convention).

Magnification: —

m = \frac{h_i}{h_o} = -\frac{v}{u}

* $m>0$ : Erect, Virtual. * $m<0$ : Inverted, Real. * $|m|>1$ : Magnified; $|m|<1$ : Diminished; $|m|=1$ : Same size.

For mirror formula signs, remember 'U-V-F': Usually Unique (object is always real, so $u$ is negative). Very Variable (image $v$ can be positive or negative). Fixed For Form (focal length $f$ is negative for concave, positive for convex).