‘रचना-प्रयोग’ का मुख्य उद्देश्य क्या है?

व्याकरण का व्यावहारिक प्रयोग सिखाना

‘द्वितीयः’ किस प्रकार की संख्या है?

क्रमवाचक (दूसरा)

Why does a ray of light bend when it enters water from air?

Light slows down in the denser medium, so it bends towards the normal — this is refraction.

What kind of mirror is used as a rear-view mirror in vehicles, and why?

A convex mirror, because it gives an erect, diminished image and a wider field of view.

State the laws of reflection of light.

The angle of incidence equals the angle of reflection, and the incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.

Where should an object be placed before a concave mirror to get a magnified, virtual image?

Between the pole and the focus; the image formed is virtual, erect and larger than the object (refer to the ray diagram in your NCERT textbook).

Why is a convex mirror used as a rear-view mirror in vehicles?

Because it always forms an erect, diminished image and gives a wider field of view of the traffic behind.

Write the mirror formula and the magnification formula.

The mirror formula is \(\frac{1}{v} + \frac{1}{u} = \frac{1}{f}\), and the magnification is \(m = \frac{-v}{u} = \frac{h\prime}{h}\).

What is refraction of light, and why does it occur?

The bending of light as it passes from one transparent medium to another; it occurs because the speed of light changes in different media.

What is the refractive index of a medium?

A measure of how much a medium slows down and bends light, given by the ratio of the speed of light in vacuum to its speed in the medium.

Write the lens formula and explain the power of a lens.

The lens formula is \(\frac{1}{v} - \frac{1}{u} = \frac{1}{f}\); the power of a lens is the reciprocal of its focal length in metres \((P = \frac{1}{f})\), measured in dioptres (D).

How does a convex lens form a real, inverted image, and where is it used?

When the object is beyond the focus, a convex lens forms a real, inverted image on the other side; such lenses are used in cameras, projectors and the human eye (refer to the ray diagram in your NCERT textbook).

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Chapter 9: Light – Reflection and RefractionClass 10 Science — summary, notes, extra questions & NCERT solutions

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According to the laws of reflection, the angle of incidence is:

Summary

Light travels in straight lines and changes direction when it meets surfaces or different media. Reflection follows two laws — the angle of incidence equals the angle of reflection, and the incident ray, reflected ray and normal lie in one plane. Spherical mirrors (concave and convex) form images whose nature, position and size are found using ray diagrams and the mirror formula 1/v + 1/u = 1/f, with magnification m = −v/u. Refraction is the bending of light as it passes from one medium to another, governed by Snell’s law and described by the refractive index. Lenses (convex and concave) form images using the lens formula 1/v − 1/u = 1/f, and the power of a lens is measured in dioptres. These ideas explain everyday optics from mirrors and magnifiers to cameras.

Reflection and spherical mirrorsMirror formula and magnificationRefraction and refractive indexLenses and the lens formulaPower of a lens

Key terms

Laws of reflection

Angle of incidence equals angle of reflection; rays and normal are coplanar.

Refractive index

A measure of how much a medium bends light.

Mirror/lens formula

Relation linking object distance, image distance and focal length.

Power of a lens

The reciprocal of focal length (in metres), measured in dioptres.

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Laws of reflection

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Angle of incidence equals angle of reflection; rays and normal are coplanar.

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Chapter 9: Light – Reflection and RefractionClass 10 Science — summary, notes, extra questions & NCERT solutions

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