Class X Physics: Light-Reflection and Refraction

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Questions and Answers

What is light? What is its nature?

Light is electromagnetic radiation visible to the human eye, characterized by its wave and particle nature.

What is the speed of light in vacuum?

299,792,458 m/s

What is a mirror?

A mirror is a reflective surface that reflects light, forming an image of an object in front of it.

What is the focal length of a plane mirror?

Infinite Signup and view all the answers

Differentiate between real and virtual image.

A real image is formed when light rays converge and can be projected on a screen, while a virtual image is formed when light rays appear to diverge from a point and cannot be projected. Signup and view all the answers

What type of image is formed on a cinema screen?

Real image Signup and view all the answers

A concave mirror is a part of a sphere of radius 40 cm. What is the focal length of the mirror?

20 cm Signup and view all the answers

Radius of curvature of a mirror is 20 cm. What type of mirror is it?

Concave mirror Signup and view all the answers

Magnification of a mirror is +2/3. What type of mirror is it?

Convex mirror Signup and view all the answers

Magnification of a mirror is -1. What type of mirror is it? What is the position of object and image? Give the nature of the image.

Concave mirror; Object at center of curvature; Image is real and inverted. Signup and view all the answers

Name the type of mirror used:

As a reflector in search light = Concave mirror As side view mirror in vehicles = Convex mirror By the dentist = Concave mirror As a shaving mirror = Concave mirror Signup and view all the answers

Wherever you may stand in front of a mirror, your image is always erect & same sized, what type of mirror is it?

Plane mirror Signup and view all the answers

A ray of light strikes the mirror at an angle of 20°. What is the angle of reflection?

20° Signup and view all the answers

Give the angle of incidence and reflection for normal incidence.

0° Signup and view all the answers

A candle is kept in front of a plane mirror at distance of 15 cm. What is the distance between candle and its image?

30 cm Signup and view all the answers

Radius of curvature of a mirror is +24 cm. Name the kind of mirror and give the characteristics of the image formed by it.

Convex mirror; Virtual, erect, and diminished image. Signup and view all the answers

Define refraction.

Refraction is the bending of light as it passes from one medium to another due to a change in its speed. Signup and view all the answers

State the laws of refraction.

<ol> <li>The incident ray, refracted ray, and normal all lie in the same plane. 2. $rac{ ext{sine of angle of incidence}}{ ext{sine of angle of refraction}}$ = constant (Snell's Law).</li> </ol> Signup and view all the answers

How does the lateral displacement depend upon the thickness of the glass slab and angle of incidence?

Lateral displacement increases with thickness and with a larger angle of incidence. Signup and view all the answers

What is the lateral displacement when a ray of light falls normally on a glass slab?

Zero Signup and view all the answers

Refractive index of water with respect to air is 1.33, what is the refractive index of air with respect to water?

0.75 Signup and view all the answers

Under what condition will the angle of refraction equal the angle of incidence?

When light travels from one medium to another with the same refractive index. Signup and view all the answers

Refractive index of glass is 1.65, what is the speed of light in glass?

1.81 x 10^8 m/s Signup and view all the answers

If refractive indices of alcohol & water are 1.36 and 1.33 respectively, which of the two is optically denser?

Alcohol Signup and view all the answers

A 1 cm high object is placed at a distance of 2F from a convex lens, what is the height of the image formed?

1.5 cm Signup and view all the answers

Focal length of a lens is 25 cm. What is its power?

+4 D Signup and view all the answers

Where should an object be placed for using a convex lens as a magnifying glass?

Within the focal length of the lens Signup and view all the answers

Power of a lens is 0.4 D. What is its focal length?

250 cm Signup and view all the answers

Why does a stick, partly immersed in water, appear to be bent? Explain with a diagram.

Due to refraction of light as it passes from water to air, creating a visual distortion. Signup and view all the answers

A small electric lamp is placed at the focus of a convex lens. What is the nature of the beam of light produced by the lens?

Parallel beam of light Signup and view all the answers

Light travels from rarer medium 1 to denser medium 2. Angle of incidence & refraction are 45° & 30° respectively. (i) Calculate the refractive index of the second medium with respect to the first. (ii) Calculate the refractive index of the first medium with respect to the second.

(i) 1.5; (ii) 0.67 Signup and view all the answers

Find the position, nature, and size of the image of an object 3 cm high placed at a distance of 9 cm from a concave mirror of focal length 18 cm.

Position: 6 cm; Nature: Real; Size: 6 cm Signup and view all the answers

An object 4 cm high is placed 40 cm in front of a concave mirror of focal length 20 cm. Find the distance from the mirror, at which a screen can be placed to obtain a sharp image.

40 cm Signup and view all the answers

A convex lens has a focal length of 30 cm. At what distance should the object be placed from the lens so that it forms an image at 60 cm on the other side of the lens? Find the magnification produced by the lens.

Object distance: 20 cm; Magnification: -1 Signup and view all the answers

An arrow 2.5 cm high is placed at a distance of 25 cm from a diverging mirror of focal length 20 cm. Find the nature, position, and size of the image formed.

Nature: Virtual; Position: 11.1 cm; Size: 1.11 cm Signup and view all the answers

The image formed by a convex mirror of focal length 30 cm is a quarter of the object, what is the distance of the object from the mirror?

90 cm Signup and view all the answers

An erect image 3 times the size of the object is obtained with a concave mirror of a radius of curvature of 36 cm. Calculate the position of the object.

12 cm Signup and view all the answers

A concave lens has a focal length of 15 cm. At what distance should an object be placed from the lens so that it forms an image at 10 cm from the lens? Find the magnification of the lens.

Object distance: -30 cm; Magnification: 1/3 Signup and view all the answers

A 2 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position, and size of the image.

Nature: Real; Position: 30 cm; Size: -4 cm Signup and view all the answers

The image obtained with a convex lens is erect and its length is 4 times the length of the object. If the focal length of the lens is 20 cm, calculate the object and image distance.

Object distance: -15 cm; Image distance: 60 cm Signup and view all the answers

Study Notes

Light and Nature

Light is an electromagnetic wave, traveling in forms that include visible light.
It exhibits both wave-like and particle-like properties, known as wave-particle duality.

Speed of Light

The speed of light in a vacuum is approximately 3 × 10^8 meters per second.

Mirrors

A mirror is a reflective surface, typically made of glass coated with a metallic film.
The focal length of a plane mirror is considered to be infinite.

Image Formation

Real images can be projected onto a screen; virtual images cannot be projected and only appear to be behind the mirror.
A cinema screen displays real images.

Concave Mirrors

For a concave mirror with a radius of 40 cm, the focal length is 20 cm.
A mirror with a radius of curvature of 20 cm is also a concave mirror.
If a mirror has a magnification of +2/3, it indicates it is a concave mirror.

Types of Mirrors

A mirror that produces an erect image of the same size from any position is a plane mirror.
Dentists use concave mirrors to examine teeth, while side view mirrors in vehicles and shaving mirrors are also concave.

Reflection Angles

If a ray strikes a mirror at an angle of 20°, the angle of reflection is also 20°.
For normal incidence, the angle of incidence equals the angle of reflection, both being 0°.

Image Distance

If a candle is 15 cm from a plane mirror, its image is the same distance away, totaling a 30 cm distance between the candle and its image.

Refractive Index and Laws of Refraction

Refractive index of water with respect to air is 1.33, making air's refractive index with respect to water approximately 0.75.
Refraction occurs when light changes speed and direction as it passes between different media.
Refraction laws state that:
- The incident ray, refracted ray, and normal all lie in the same plane.
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant (Snell's Law).

Lateral Displacement

Lateral displacement increases with thicker glass slabs and varies with the angle of incidence.
If light strikes a glass slab normally, lateral displacement is zero.

Focal Length and Power of Lenses

The power of a lens is the reciprocal of its focal length in meters. A 25 cm lens has a power of +4 D.
Convex lenses used as magnifying glasses require the object to be placed within the focal length.

Optical Phenomena

A partially immersed stick appears bent due to refraction.
An electric lamp at the focus of a convex lens produces a parallel beam of light.

Image Characteristics

An object 2 cm high placed 10 cm from a convex lens (focal length 10 cm) produces an image 4 cm high and 30 cm away.
For a convex lens with a focal length of 20 cm, if the image is 4 times the size of the object, calculations yield specific distances for both object and image.
Different types of mirrors and their corresponding focal lengths yield diverse image characteristics, such as size, nature (real or virtual), and orientation.

Practical Applications

Concave mirrors can magnify images, useful in various practical applications such as makeup mirrors and reflecting telescopes.
Diverging mirrors, also known as concave mirrors, produce smaller, upright images.

This guide encapsulates key concepts related to light, mirrors, lenses, and optical phenomena essential for the understanding of reflections and refractions in physics.

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Description

Test your understanding of key concepts in light, reflection, and refraction through this assignment. Answer questions on the nature of light, the characteristics of mirrors, and the formation of images. Ideal for Class X physics students preparing for exams.