Reflection and Mirrors
NCERT Class 10 • Science • Chapter "Light Reflection and Refraction" | NCERT Class 8 • Science • Chapter "Light"
Reflection and Mirrors
Light travels in a straight line and is a form of energy that lets us see. When light falls on a surface and bounces back into the same medium, the effect is called reflection, and it is what makes mirrors, periscopes and vehicle rear view systems possible.
Laws of Reflection and the Plane Mirror
- The first law states that the angle of incidence equals the angle of reflection.
- The second law states that the incident ray, the reflected ray and the normal all lie in the same plane.
- Regular reflection happens on a smooth surface and gives a clear image; diffuse reflection on a rough surface scatters light.
- A plane mirror forms an image that is virtual, erect, of the same size, and as far behind the mirror as the object is in front.
- The image in a plane mirror shows lateral inversion, which is why the word AMBULANCE is painted reversed on vehicles.
- A real image can be taken on a screen; a virtual image cannot.
Spherical Mirrors and Their Uses
- A concave mirror curves inward and converges parallel rays to its principal focus.
- A concave mirror gives an enlarged erect virtual image when the object is very close, and a real inverted image beyond the focus.
- It is used as a shaving mirror, in a dentist's mirror, in a torch and headlight reflector, and in solar cookers.
- A convex mirror curves outward and diverges parallel rays, so the focus is virtual.
- A convex mirror always gives a virtual, erect and diminished image and covers a wide field of view.
- It is used as a vehicle rear view mirror and in shops and street corners for surveillance.
- The focal length of a spherical mirror is half its radius of curvature.
| Mirror | Nature of Image | Common Use |
|---|---|---|
| Plane | Virtual, erect, same size | Household mirror |
| Concave | Real or virtual, depends on distance | Headlight, shaving mirror |
| Convex | Always virtual, erect, diminished | Rear view mirror |
Lateral inversion — the apparent left to right reversal of an image formed by a plane mirror.
Hindi me samjhein
अवतल दर्पण प्रकाश को एक बिंदु पर मिलाता है, इसलिए उसे अभिसारी कहते हैं। उत्तल दर्पण प्रकाश को फैलाता है, इसलिए वह अपसारी है और हमेशा छोटा सीधा प्रतिबिंब देता है।
Exam me kaise aata hai
- Which mirror is used as a rear view mirror — convex mirror
- Which mirror is used in a torch reflector — concave mirror
- Left to right reversal in a plane mirror is called — lateral inversion
- Focal length equals what fraction of radius of curvature — half
UPSC/State PSC ke liye
- A convex mirror is chosen for vehicles because it always gives an erect image and a wider field of view, even though the image is smaller.
- Diffuse reflection is why we can see non luminous objects from every direction rather than only along one line.
Yahan confuse hote hain
✗ A plane mirror gives a real image | A plane mirror gives a virtual image | ✓
✗ A convex mirror can give a real image | A convex mirror always gives a virtual image | ✓
✗ Concave and convex mirrors both converge light | Concave converges; convex diverges | ✓
Ek nazar me
- Angle of incidence equals angle of reflection, and both rays lie in one plane with the normal.
- A plane mirror gives a virtual, erect, same size image with lateral inversion.
- Concave converges and is used in headlights and solar cookers.
- Convex diverges, always gives a small erect image, and is used as rear view mirror.