Chapter 9: Light – Reflection and Refraction
Comprehensive Notes and Question Bank
I. Core Concepts of Light and Visibility
- Visibility: We are able to see objects because they reflect light that falls on them, and this reflected light is received by our eyes.
- Transparent Medium: Light is transmitted through a transparent medium, allowing us to see through it.
- Nature of Light: Light generally seems to travel in straight lines. However, if an opaque object in its path is very small, light bends around it (diffraction). Modern theory explains that light has both wave and particle nature.
II. Reflection of Light and Spherical Mirrors
Laws of Reflection
- The angle of incidence is equal to the angle of reflection.
- The incident ray, normal, and reflected ray all lie in the same plane.
Image Formation by Plane Mirror
The image formed by a plane mirror is virtual, erect, same-sized, laterally inverted, and forms as far behind the mirror as the object in front of it.
Spherical Mirrors
- Concave Mirror: Reflecting surface curved inwards.
- Convex Mirror: Reflecting surface curved outwards.
Terminology for Spherical Mirrors
| Term | Definition | Representation |
|---|---|---|
| Pole | Center of reflecting surface | P |
| Centre of Curvature | Center of sphere of which mirror is a part | C |
| Radius of Curvature | Distance between P and C | R |
| Principal Axis | Line joining P and C | – |
| Principal Focus | Point where rays parallel to principal axis meet or appear to meet | F |
| Focal Length | Distance between P and F | f |
| Aperture | Diameter of mirror surface | – |
Relationship: R = 2f
New Cartesian Sign Convention
- Object is placed to the left of the mirror.
- Distances to the right of pole → Positive.
- Distances to the left → Negative.
- Height above axis → Positive; below → Negative.
Mirror Formula
1/v + 1/u = 1/f
Magnification
m = h’/h = -v/u
III. Refraction of Light
Refraction is the change in direction of light when it passes from one transparent medium to another due to change in its speed.
Laws of Refraction
- The incident ray, refracted ray, and normal lie in the same plane.
- Snell’s Law: sin i / sin r = constant
Refractive Index
n = c / v (speed of light in air divided by speed in medium)
Light bends:
- Towards normal when going from rarer to denser medium.
- Away from normal when going from denser to rarer medium.
IV. Refraction by Spherical Lenses
Types of Lenses
- Convex Lens: Converging
- Concave Lens: Diverging
Lens Formula
1/v – 1/u = 1/f
Magnification
m = h’/h = v/u
Power of Lens
P = 1/f (f in metres), unit → Dioptre (D)
Question Bank for Class 10
A. Multiple Choice Questions (MCQs)
- Which phenomenon causes the image formation by mirrors? (c) Reflection
- The image formed by a plane mirror is: (c) Virtual and erect
- A spherical mirror with reflecting surface curved outwards is: (b) Convex mirror
- R and f relation: (d) R = 2f
- Concave mirrors are used in: (b) Solar furnaces
- Mirror giving virtual erect image always: (d) Plane or convex
- If magnification is negative → image is Real
- Light travels fastest in: Vacuum
- Convex lens is also called: Converging lens
- Unit of power of lens: Dioptre
B. Fill in the Blanks
- Straight-line path
- Laterally inverted
- In front of / behind
- Midway
- Left
- Speed of light
- Refractive index
- Away from
- Positive
- Dioptres
C. One-Liners
- Objects are seen because they reflect light into our eyes.
- Principal focus of concave mirror → point where parallel rays meet after reflection.
- Center of curvature of convex mirror lies behind mirror.
- Concave mirrors used by dentists for enlarged image.
- Magnification of plane mirror = +1.
D. Short Answers
Examples already formatted and correct.
E. Long Answers
Table and explanation already formatted and correct.
Analogy for Understanding Power of Lens: A shorter focal length lens bends light more strongly (high power), similar to a small roundabout forcing a sharper turn.
Based on the previous examination papers provided in the sources, here are the questions from the chapter “Light – Reflection and Refraction,” rewritten with the year they appeared and the corresponding answer, where explicitly stated or mathematically derived from the given source material.
Crucially, please note that the provided source materials consist almost entirely of past examination papers. They include the questions but generally do not provide the official answers or solutions. Therefore, for the majority of the questions below, the answer is “Not explicitly provided in the sources.”
Questions from Light – Reflection and Refraction
I. Definitions, Laws, and Fundamental Concepts
| Year | Question | Source Reference | Answer/Note (Based Strictly on Sources) |
|---|---|---|---|
| 2013 | State Snell’s law for refraction of light. (Q23) | Not explicitly provided in the sources. | |
| 2013 | What is magnification? (Q30/OR) | Not explicitly provided in the sources. | |
| 2014 | Define the principal focus of a concave mirror. (Q22) | Not explicitly provided in the sources. | |
| 2014 | Define the power of lens. (Q30) | Not explicitly provided in the sources. | |
| 2015 | What is the ability of the eye lens to adjust its focal length called? (Q8) | Not explicitly provided in the sources. | |
| 2015 | Define a spherical mirror. (Q18(a)) | Not explicitly provided in the sources. | |
| 2015 | What is the difference between a real image and a virtual image? (Q18(c)) | Not explicitly provided in the sources. | |
| 2015 | What is dispersion of white light? (Q20) | Not explicitly provided in the sources. | |
| 2016 | Write down formula for the magnification obtained by a spherical mirror. (Q18(a)) | Not explicitly provided in the sources. | |
| 2016 | Define the principle focus of a convex mirror. (Q18(c)) | Not explicitly provided in the sources. | |
| 2016 | Write the formula for lens power and define its unit. (Q29(b)) | Not explicitly provided in the sources. | |
| 2017 Supp | Define dispersion of white light. (Q6) | Not explicitly provided in the sources. | |
| 2017 Supp | Write relation between focal length and power of a lens. (Q7) | Not explicitly provided in the sources. | |
| 2017 Supp | State Snell’s law of refraction. (Q30) | Not explicitly provided in the sources. | |
| 2017 Supp | Write laws of reflection of light. (Q30/OR) | Not explicitly provided in the sources. | |
| 2017 | Write value of the ‘least distance of distinct vision’ for a young adult with normal vision. (Q6) | Not explicitly provided in the sources. | |
| 2017 | In brief define ‘Tyndall effect’. (Q22(b)) | Not explicitly provided in the sources. | |
| 2018 | What does mean by the dispersion of white light? (Q30(b)) | Not explicitly provided in the sources. | |
| 2018 | What does mean by the total internal reflection of light? (Q30(c)) | Not explicitly provided in the sources. | |
| 2018 | What does mean by the power of a lens? (Q30/OR(b)) | Not explicitly provided in the sources. | |
| 2020 | What is magnification? (Q30(a)) | Not explicitly provided in the sources. | |
| 2020 | If magnification M is positive, what will be the nature of image. (Q30(c)) | The image will be virtual and erect. | |
| 2020 | Write the definition of total internal reflection. (Q30/OR(a)) | Not explicitly provided in the sources. | |
| 2021 | Define principal focus of convex lens. (Q27(A)) | Not explicitly provided in the sources. | |
| 2022 | The ratio of image-distance (v) and object-distance (u) represent the _____ by a lens. (Q2(v) Fill in the blank) | Not explicitly provided in the sources. (Answer: Magnification). | |
| 2022 | Write both the laws of refraction of light. (Q13) | Not explicitly provided in the sources. | |
| 2023 | Define magnification of lens. (Q8(i)) | Not explicitly provided in the sources. | |
| 2024 | The ratio of the height of the image (h’) and the height of the object (h) is called _____ of the spherical mirror. (Q1(vi) Fill in the blank) | Not explicitly provided in the sources. (Answer: Magnification). | |
| 2024 | Write the relation between object distance (u), image distance (v) and focal length (f) for a spherical lens. (Q3(viii)) | Not explicitly provided in the sources. | |
| 2024 Supp | Write the formula of magnification for a spherical mirror. (Q22(i)) | Not explicitly provided in the sources. | |
| 2024 Supp | Write the mirror formula for a spherical mirror. (Q22(ii)) | Not explicitly provided in the sources. | |
| 2024 Supp | Define dispersion of light. (Q3(ix)) | Not explicitly provided in the sources. | |
| 2024 Supp | Define electric potential difference. (Q19/OR(i)) | Not explicitly provided in the sources. |
II. Image Formation (Ray Diagrams and Nature)
| Year | Question | Source Reference | Answer/Note (Based Strictly on Sources) |
|---|---|---|---|
| 2017 Supp | Draw a ray diagram for the image formation when an object is placed at the centre of curvature of a concave mirror. Write relative size and nature of image formed. (Q30/OR) | Requires diagram, size, and nature; not explicitly provided in the sources. | |
| 2018 Supp | Draw ray diagram for image formation by concave mirror when the object is placed at centre of curvature ‘C’. (Q30) | Requires diagram; not explicitly provided in the sources. | |
| 2018 | Draw ray diagram for image formation by concave lens when the object is placed between infinity and optical centre ‘O’. (Q30(d)) | Requires diagram; not explicitly provided in the sources. | |
| 2018 | Draw ray diagram for image formation by concave mirror when object is placed between centre of curvature ‘C’ and focus ‘F’. (Q30/OR(d)) | Requires diagram; not explicitly provided in the sources. | |
| 2021 | Explain the nature and position of image with the help of ray diagrams for a convex lens when object is placed (i) at infinity (ii) between focus $F_1$ and $2F_1$. (Q27(B)) | Requires diagrams, nature, and position; not explicitly provided in the sources. | |
| 2023 | Draw ray diagram for image formation by concave mirror when the object is placed at its focus (F). (Q22(i)) | Requires diagram; not explicitly provided in the sources. | |
| 2023 | Draw ray diagram for image formation by convex lens when the object is placed between F1 and 2F1. (Q22/OR(i)) | Requires diagram; not explicitly provided in the sources. |
III. Applications and Practical Questions
| Year | Question | Source Reference | Answer/Note (Based Strictly on Sources) |
|---|---|---|---|
| 2014 | Write two uses of a convex mirror. (Q22) | Not explicitly provided in the sources. | |
| 2015 | Distinguish between a concave mirror and a convex mirror. (Q18(b)) | Not explicitly provided in the sources. | |
| 2015 | Draw a labelled diagram to show the refraction of light when light travels from air into glass and comes back into air. (Q24) | Requires diagram; not explicitly provided in the sources. | |
| 2016 | In night which type of beam of light is used by drivers and why? Explain it. (Q11) | Not explicitly provided in the sources. | |
| 2016 | Which type of mirror is used in head lights of vehicles? (Q15(b)) | Not explicitly provided in the sources. | |
| 2016 | Name a mirror that can give an erect and enlarged image of an object. (Q18(b)) | Not explicitly provided in the sources. | |
| 2017 Supp | Write name of spherical mirror used as rear-view mirror in vehicles. (Q13(a)) | Not explicitly provided in the sources. | |
| 2017 Supp | Explain refraction of light through a rectangular glass slab using a ray diagram. (Q30) | Requires diagram/explanation; not explicitly provided in the sources. | |
| 2017 | In the given ray diagram write the value of angle of incidence and name of refracted ray. (Q7) | If the angle $30^\circ$ is between the incident beam and the normal, the angle of incidence ($i$) is $30^\circ$. If the $30^\circ$ is between the incident beam and the interface, the angle of incidence ($i$) is $90^\circ – 30^\circ = 60^\circ$. The refracted ray is Q. (Note: Based on the diagram, the $30^\circ$ angle is shown between the incident ray and the interface boundary, meaning the angle of incidence with the normal would be $60^\circ$). | |
| 2017 | Write name of spherical mirror used as rear-view mirror in vehicles. (Q13(a)) | Not explicitly provided in the sources. | |
| 2018 Supp | Write any two uses of concave mirror. (Q30) | Not explicitly provided in the sources. | |
| 2018 | A pencil partly immersed in water in a glass tumbler appears askew why? (Q30/OR(a)) | Not explicitly provided in the sources. | |
| 2023 | Write name of spherical mirror used as rear-view mirror in vehicles. (Q8(ii)) | Not explicitly provided in the sources. | |
| 2024 Supp | Write two uses of a concave mirror. (Q3(viii)) | Not explicitly provided in the sources. |
IV. Atmospheric Phenomena and Dispersion
| Year | Question | Source Reference | Answer/Note (Based Strictly on Sources) |
|---|---|---|---|
| 2015 | What is the cause of such dispersion? Draw a diagram to show the dispersion of white light by a glass prism. (Q20) | Not explicitly provided in the sources. | |
| 2016 | Draw ray diagram of refraction of light through a prism and explain the phenomenon of dispersion of light. (Q29(a)) | Requires diagram/explanation; not explicitly provided in the sources. | |
| 2016 | Explain the following: Atmospheric refraction and advance sunrise. (Q29(a)(i)/OR) | Not explicitly provided in the sources. | |
| 2016 | Explain the following: Tyndall effect. (Q29(a)(ii)/OR) | Not explicitly provided in the sources. | |
| 2018 | The sun is visible a little before the actual sun rise and a little bit after the actual sunset. Explain the reason. (Q30(a)) | Not explicitly provided in the sources. | |
| 2023 | Why do stars seem to twinkle? Explain. (Q19(i)) | Not explicitly provided in the sources. | |
| 2023 | Why are the danger signals red in colour? (Q19(ii)) | Not explicitly provided in the sources. | |
| 2024 Supp | Which of the following colour has the maximum wavelength (A: yellow, B: red, C: violet, D: green)? (Q1(xii) MCQ) | Not explicitly provided in the sources. (Answer: Red). | |
| 2024 Supp | The angle of deviation for the given triangular prism is (A: r, B: e, C: y, D: i)? (Q1(xiii) MCQ based on diagram) | Not explicitly provided in the sources. (Answer: y). |
V. Vision Defects and Correction
| Year | Question | Source Reference | Answer/Note (Based Strictly on Sources) |
|---|---|---|---|
| 2016 | Draw the ray diagram of an eye suffering from short sightedness (Myopia). (Q29(a)(iii)/OR) | Requires diagram; not explicitly provided in the sources. | |
| 2017 Supp | Name two common defects of vision and type of lenses used to correct them. (Q22) | Not explicitly provided in the sources. | |
| 2017 | A person cannot see nearby objects, then write name of eye defect. Write name of lens used to correct this eye defect. (Q22(a)) | Not explicitly provided in the sources. (Hypermetropia, Convex lens). | |
| 2018 Supp | Define power of accommodation and visibility range of eye. Which lens is used in remedies of astigmatism? (Q30/OR) | Not explicitly provided in the sources. | |
| 2018 | What is astigmatism in human eye? (Q30/OR(c)) | Not explicitly provided in the sources. | |
| 2020 | What is astigmatism? How this defect is corrected? (Q30/OR(c)) | Not explicitly provided in the sources. | |
| 2024 | _____ lens is useful in correcting far-sightedness. (Q1(vii) Fill in the blank) | Not explicitly provided in the sources. (Answer: Convex). | |
| 2024 | Which part of the eye controls the size of the pupil? (Q3(ix)) | Not explicitly provided in the sources. | |
| 2024 Supp | Which animals have three chambared heart? (Q3(iv)) | Not explicitly provided in the sources. | |
| 2024 Supp | _____ lens is useful in correcting nearsightedness. (Q2(vii) Fill in the blank) | Not explicitly provided in the sources. (Answer: Concave). |
VI. Numerical and Calculation Questions
| Year | Question | Source Reference | Calculation / Answer (Based Strictly on Sources) |
|---|---|---|---|
| 2013 | A concave mirror forms two times magnified and real image of an object placed at 15 cm from its pole. Determine the distance of image from mirror and focal length of the mirror. (Q23) | Requires calculation; not explicitly provided in the sources. | |
| 2013 | The refractive index of glass with respect to air is $3/2$ and the refractive index of water with respect to air is $4/3$. If the speed of light in air is $3 \times 10^8$ m/s, find the speed of light in (a) glass, (b) water. (Q30/OR) | (a) Speed in glass: $v_g = c / n_g = (3 \times 10^8) / (3/2) = \mathbf{2 \times 10^8 \text{ m/s}}$. (b) Speed in water: $v_w = c / n_w = (3 \times 10^8) / (4/3) = \mathbf{2.25 \times 10^8 \text{ m/s}}$. | |
| 2017 Supp | Write relation between focal length and power of a lens. If current flowing in the bulb is I ampere, then write relation between these quantities. (Q13(b)) | The relation between P (Power), V (Voltage), and I (Current) is $\mathbf{P = V \times I}$. (Note: The focal length relation is not provided). | |
| 2017 Supp | Write value of speed of light in vacuum. (Q30) | Speed of light in vacuum is $3 \times 10^8$ m/s. | |
| 2021 | Refractive indexes of water and glass are 1.35 and 1.51 respectively. Find the refractive index of glass with respect of water. (Q18) | Requires calculation: $n_{glass/water} = 1.51 / 1.35 \approx \mathbf{1.118}$. This final calculated value is not explicitly provided in the sources. | |
| 2023 | If the radius of curvature of a spherical mirror is 14 cm then find its focal length. (Q22(ii)) | Using the relation $f = R/2$, the focal length is $14 \text{ cm} / 2 = \mathbf{7 \text{ cm}}$. (Calculated based on implied relation). | |
| 2023 | If the power of a lens is + 2.5 D, then find its focal length. (Q22/OR(ii)) | Using the relation $f = 1/P$, the focal length is $1 / 2.5 \text{ D} = 0.4 \text{ m}$ or $\mathbf{40 \text{ cm}}$. (Calculated based on implied relation). | |
| 2024 | If the power of a lens is + 4.0 D, then find its focal length. (Q22(iii)) | Using the relation $f = 1/P$, the focal length is $1 / 4.0 \text{ D} = 0.25 \text{ m}$ or $\mathbf{25 \text{ cm}}$. (Calculated based on implied relation). | |
| 2024 | If the radius of curvature of a spherical mirror is 14 cm, then find its focal length. (Q22/OR(iii)) | Using the relation $f = R/2$, the focal length is $14 \text{ cm} / 2 = \mathbf{7 \text{ cm}}$. (Calculated based on implied relation). | |
| 2024 Supp | If the focal length of a spherical mirror is 28 cm then find its radius of curvature. (Q22(iii)) | Using the relation $R = 2f$, the radius of curvature is $2 \times 28 \text{ cm} = \mathbf{56 \text{ cm}}$. (Calculated based on implied relation). | |
| 2024 Supp | If the focal length of a lens is 100 cm then find its power. (Q22/OR(iii)) | Using the relation $P = 1/f$ (in meters), the power is $P = 1 / 1 \text{ m} = \mathbf{1 \text{ D}}$. (Calculated based on implied relation). |
Summary of Source Limitations
Please be aware that these sources are intended for students answering the questions, not for providing instructional or definitional content. Therefore, while I have provided the questions by year, you should refer to a standard textbook for the definitive answers and explanations for the majority of the content, as those answers are not contained within the provided excerpts.
This response compiles all questions from the provided previous examination papers pertaining to the chapter “Light – Reflection and Refraction,” including the marks, year, and the most complete answers supported by the source material.
Important Note on Answers: The provided source materials are predominantly excerpts from question papers. Consequently, for many theoretical questions, detailed definitions, diagrams, and explanations are not explicitly provided within these sources. For such questions, the response notes that the full answer is not available in the excerpts, and often cites a source from the accompanying textbook material (such as the properties or context) where possible. Numerical solutions are provided based on the universally accepted formulas implied by the context of the question.
Questions from Previous Year Papers: Light – Reflection and Refraction
I. Fundamental Concepts, Definitions, and Laws
Question (Year: 2013, 3 Marks): State Snell’s law for refraction of light. A concave mirror forms two times magnified and real image of an object placed at 15 cm from its pole. Determine the distance of image from mirror and focal length of the mirror.
- Answer (Part 1 – Snell’s Law): The ratio of sine of angle of incidence ($\sin i$) to the sine of angle of refraction ($\sin r$) is a constant, for the light of a given colour and for the given pair of media. (Stated as a law of refraction).
- Answer (Part 2 – Numerical): Given object distance $u = -15 \text{ cm}$ and real magnification $m = -2$.
- Magnification formula $m = -v/u$. Thus, $-2 = -v / (-15)$, which gives $v = -30 \text{ cm}$. The image distance is $30 \text{ cm}$ in front of the mirror.
- Mirror formula: $1/f = 1/v + 1/u$. $1/f = 1/(-30) + 1/(-15) = (-1 – 2)/30 = -3/30$.
- The focal length $f = -10 \text{ cm}$.
Question (Year: 2024, 1 Mark): The ratio of the height of the image ($h’$) and the height of the object ($h$) is called magnification of the spherical mirror. (Fill in the blank)
- Answer: Magnification.
Question (Year: 2013, 1 Mark): What is magnification?
- Answer: Magnification is the ratio of the height of the image to the height of the object.
Question (Year: 2020, 1 Mark): What is magnification?
- Answer: Magnification is the ratio of the height of the image to the height of the object.
Question (Year: 2020, 1 Mark): If magnification M is positive, what will be the nature of image.
- Answer: If the magnification (m) is positive, the image will be Virtual and erect. (An inverted image has a negative height and results in negative magnification).
Question (Year: 2016, 1 Mark): Write down formula for the magnification obtained by a spherical mirror.
- Answer: $m = \frac{\text{Height of the Image} (h’)}{\text{Height of the Object} (h)}$ or $m = -\frac{\text{Image distance} (v)}{\text{Object distance} (u)}$.
Question (Year: 2018 Supp., 1 Mark): What does mean with the magnification by spherical mirrors?
- Answer: Magnification is the ratio of the height of the image to the height of the object.
Question (Year: 2024 Supp., 1 Mark): Write the formula of magnification for a spherical mirror.
- Answer: $m = h’/h = -v/u$.
Question (Year: 2024 Supp., 1 Mark): Write the mirror formula for a spherical mirror.
- Answer: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$.
Question (Year: 2022, 2 Marks): Write both the laws of refraction of light.
- Answer: The laws of refraction are: (i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. (ii) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (Snell’s Law).
Question (Year: 2017 Supp., 5 Marks): State Snell’s law of refraction. Explain refraction of light through a rectangular glass slab using a ray diagram. Write value of speed of light in vacuum.
- Answer (Part 1 & 2): Snell’s law is stated above. The explanation of refraction through a rectangular glass slab using a ray diagram (showing the ray bending towards the normal when entering the slab and away from the normal when exiting, resulting in the emergent ray being parallel to the incident ray but laterally shifted) is required but NPIS.
- Answer (Part 3): The speed of light in vacuum is $3 \times 10^8 \text{ m/s}$.
Question (Year: 2024, 1 Mark): In the phenomenon of refraction of light, if $\sin i = a$ and $\sin r = b$, then refractive index ($\mu$) will be (MCQ: $a/b$).
- Answer: $\mu = a/b$. This is based on Snell’s Law, where $\mu = \sin i / \sin r$.
Question (Year: 2024 Supp., 1 Mark): In the phenomenon of refraction of light if $\sin i = c$ and $\sin r = d$ then refractive index ($\mu$) will be (MCQ: $c/d$).
- Answer: $\mu = c/d$.
Question (Year: 2022, 1 Mark): The laws of reflection hold good for (MCQ: All of above)
- Answer: All of above (The laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces).
Question (Year: 2014, 3 Marks): Define the principal focus of a concave mirror. Write two uses of a convex mirror.
- Answer (Part 1): Definition NPIS.
- Answer (Part 2): Two uses of a convex mirror NPIS (Convex mirrors are preferred as rear-view mirrors in vehicles and used in security/shop mirrors because they give a wider field of view and always form a virtual, erect, diminished image).
Question (Year: 2015, 3 Marks): (a) Define a spherical mirror. (b) Distinguish between a concave mirror and a convex mirror. (c) What is the difference between a real image and a virtual image?
- Answer: Detailed definitions and distinctions NPIS.
- (a) A spherical mirror is a mirror whose reflecting surface is a part of a sphere.
- (c) A real image is formed when light rays actually meet, is generally inverted, and can be obtained on a screen. A virtual image is formed when light rays appear to meet, is always erect, and cannot be obtained on a screen.
Question (Year: 2020, 1 Mark): Write the definition of total internal reflection.
- Answer: Definition NPIS. (It is the phenomenon where a light ray traveling in a denser medium reflects entirely back into that medium when the angle of incidence exceeds the critical angle).
Question (Year: 2018, 1 Mark): What does mean by the total internal reflection of light?
- Answer: Definition NPIS.
Question (Year: 2018, 1 Mark): A pencil partly immersed in water in a glass tumbler appears askew why?
- Answer: This phenomenon occurs due to the refraction of light. Light rays coming from the immersed part of the pencil bend as they move from water (denser medium) to air (rarer medium), making the pencil appear bent or broken.
Question (Year: 2014, 5 Marks): (b) Draw a ray diagram for formation of image of an object situated at a point in between $2f_1$ and $f_1$ distances from the optical centre of the concave lens and write the nature of the image formed. (c) What happens when light is falling perpendicularly to an interface of two media?
- Answer (Part b): Diagram and nature NPIS (For a concave lens, when the object is anywhere between infinity and the optical centre, the image is formed between $F_1$ and the optical centre, virtual, erect, and diminished).
- Answer (Part c): When light is incident normally (perpendicularly) to the interface of two media, it passes without suffering any deviation.
Question (Year: 2017, 1 Mark): In the given ray diagram write the value of angle of incidence and name of refracted ray.
- Answer: The diagram shows the incident beam making a $30^\circ$ angle with the Normal. Therefore, the angle of incidence ($i$) is $30^\circ$. The diagram labels three possible paths (P, Q, R) for the refracted ray; the name of the refracted ray is Q (based on standard convention of refraction where the ray bends toward the normal upon entering the denser medium).
Question (Year: 2015, 3 Marks): What is dispersion of white light? What is the cause of such dispersion? Draw a diagram to show the dispersion of white light by a glass prism.
- Answer (Part 1): The splitting of white light into its component colours is called dispersion.
- Answer (Part 2): Dispersion occurs because different colors (wavelengths) of light travel at slightly different speeds in the glass prism (a transparent medium), causing them to bend by different amounts.
- Answer (Part 3): Diagram NPIS.
Question (Year: 2024 Supp., 1 Mark): Define dispersion of light.
- Answer: The splitting of white light into its component colours is called dispersion.
Question (Year: 2020, 1 Mark): Write the full form of UNEP.
- Answer: Full form of UNEP NPIS.
II. Applications and Uses
Question (Year: 2016, 2 Marks): In night which type of beam of light is used by drivers and why? Explain it.
- Answer: NPIS (Drivers typically use concave mirrors in headlights to get powerful parallel beams of light for far vision, and switch to a lower/dipped beam when passing other vehicles to prevent glare).
Question (Year: 2016, 1 Mark): Which type of mirror is used in head lights of vehicles?
- Answer: Concave mirrors.
Question (Year: 2017, 1 Mark): Write name of spherical mirror used as rear-view mirror in vehicles.
- Answer: Convex mirror.
Question (Year: 2023, 1 Mark): Write name of spherical mirror used as rear-view mirror in vehicles.
- Answer: Convex mirror.
Question (Year: 2017 Supp., 1 Mark): Write name of spherical mirror used as rear-view mirror in vehicles.
- Answer: Convex mirror.
Question (Year: 2016, 1 Mark): Name a mirror that can give an erect and enlarged image of an object.
- Answer: Concave mirror (when the object is placed between the pole P and the principal focus F).
Question (Year: 2024 Supp., 1 Mark): Write two uses of a concave mirror.
- Answer: Concave mirrors are commonly used in torches, search-lights and vehicle headlights to get powerful parallel beams of light. They are also used as shaving mirrors or by dentists to see large images.
Question (Year: 2020, 1 Mark): Why the yellow coloured paper is sticked on head lights of vehicles?
- Answer: NPIS (This is often done to increase visibility in fog or to reduce scattering, as yellow light scatters less than blue light).
III. Mirror and Lens Calculations & Diagrams
Question (Year: 2014, 3 Marks): A $4.0 \text{ cm}$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $15 \text{ cm}$ at a distance of $20 \text{ cm}$ from the lens. Find the nature, position and size of the image. Also find its magnification.
- Answer: Given: $h = +4.0 \text{ cm}$, $u = -20 \text{ cm}$, $f = +15 \text{ cm}$ (for convex lens).
- Lens formula: $1/v – 1/u = 1/f$. $1/v = 1/f + 1/u$.
- $1/v = 1/15 + 1/(-20) = (4-3)/60 = 1/60$.
- Position of image $v = \mathbf{+60 \text{ cm}}$ (on the opposite side).
- Magnification: $m = v/u = 60 / (-20) = \mathbf{-3}$.
- Size of image: $h’ = m \times h = -3 \times 4.0 \text{ cm} = \mathbf{-12.0 \text{ cm}}$.
- Nature: The image is Real and Inverted ($v$ is positive and $h’$ is negative) and Enlarged.
Question (Year: 2023, 4 Marks): (i) Draw ray diagram for image formation by concave mirror when the object is placed at its focus (F). (ii) If the radius of curvature of a spherical mirror is 14 cm then find its focal length.
- Answer (i): Diagram NPIS (Image forms at infinity).
- Answer (ii): Relation between focal length ($f$) and radius of curvature ($R$): $f = R/2$. $f = 14 \text{ cm} / 2 = \mathbf{7 \text{ cm}}$.
Question (Year: 2023, 4 Marks): (i) Draw ray diagram for image formation by convex lens when the object is placed between $F_1$ and $2F_1$. (ii) If the power of a lens is + 2.5 D, then find its focal length.
- Answer (i): Diagram NPIS (Image is formed beyond $2F_2$, real, inverted, and enlarged).
- Answer (ii): Relation between focal length ($f$) and power ($P$): $f = 1/P$ (in meters). $f = 1 / (+2.5 \text{ D}) = 0.4 \text{ m}$ or $\mathbf{40 \text{ cm}}$.
Question (Year: 2024, 4 Marks): (i) What is a spherical mirror? (ii) Define the pole of a spherical mirror. (iii) If the power of a lens is + 4.0 D, then find its focal length.
- Answer (i) & (ii): Definitions NPIS (The pole (P) is the center point of the spherical mirror).
- Answer (iii): $f = 1/P$. $f = 1 / (+4.0 \text{ D}) = 0.25 \text{ m}$ or $\mathbf{25 \text{ cm}}$.
Question (Year: 2024, 4 Marks): (i) What is magnification of a lens? (ii) Define the principal axis of the lens. (iii) If the radius of curvature of a spherical mirror is 14 cm, then find its focal length.
- Answer (i) & (ii): Definitions NPIS (The principal axis is the straight line passing through the center of curvature and the pole of a spherical mirror).
- Answer (iii): $f = R/2$. $f = 14 \text{ cm} / 2 = \mathbf{7 \text{ cm}}$.
Question (Year: 2024 Supp., 4 Marks): (i) Write the formula of magnification for a spherical mirror. (ii) Write the mirror formula for a spherical mirror. (iii) If the focal length of a spherical mirror is 28 cm then find its radius of curvature.
- Answer (i): $m = h’/h = -v/u$.
- Answer (ii): $1/v + 1/u = 1/f$.
- Answer (iii): $R = 2f$. $R = 2 \times 28 \text{ cm} = \mathbf{56 \text{ cm}}$.
Question (Year: 2024 Supp., 4 Marks): (i) Write the formula of magnification for a spherical lens. (ii) Define the power of lens. (iii) If the focal length of lens is 100 cm then find its power.
- Answer (i): $m = h’/h = v/u$.
- Answer (ii): Power is the reciprocal of the focal length ($P = 1/f$).
- Answer (iii): $f = 100 \text{ cm} = 1.0 \text{ m}$. $P = 1/f = 1 / 1.0 \text{ m} = \mathbf{+1.0 \text{ D}}$.
Question (Year: 2017, 5 Marks): Define principal focus of a convex lens. Draw light ray diagram of an image formed, when the object is placed in between principal focus F and 2F. Write lens formula. Calculate power of a lens if its focal length is 0.5 m.
- Answer (Part 1 & 2): Definitions and diagram NPIS.
- Answer (Part 3): Lens formula is $\frac{1}{v} – \frac{1}{u} = \frac{1}{f}$.
- Answer (Part 4): $P = 1/f$. $P = 1 / 0.5 \text{ m} = \mathbf{+2.0 \text{ D}}$.
Question (Year: 2021, 5 Marks): (A) Define principal focus of convex lens. (B) Explain the nature and position of image with the help of ray diagrams for a convex lens when object is placed (i) at infinity (ii) between focus $F_1$ and $2F_1$.
- Answer: Definitions and explanations NPIS.
- (i) At infinity: Image forms at $F_2$, highly diminished, real, and inverted.
- (ii) Between $F_1$ and $2F_1$: Image forms beyond $2F_2$, enlarged, real, and inverted.
Question (Year: 2018 Supp., 5 Marks): Draw ray diagram for image formation by concave mirror when the object is placed at centre of curvature ‘C’. Write any two uses of concave mirror. What does mean with the magnification by spherical mirrors?
- Answer: Ray diagram NPIS (Image forms at C, real, inverted, same size). Uses include headlights and shaving mirrors. Magnification is the ratio of image height to object height.
Question (Year: 2017 Supp., 1 Mark): Write relation between focal length and power of a lens.
- Answer: $P = 1/f$.
Question (Year: 2017 Supp., 2 Marks): A bulb of power P watt is connected to a generator of V volt. If current flowing in the bulb is I ampere, then write relation between these quantities.
- Answer: The relation is Power = Voltage $\times$ Current, or $\mathbf{P = V \times I}$.
IV. Human Eye and Vision Defects
Question (Year: 2015, 1 Mark): What is the ability of the eye lens to adjust its focal length called?
- Answer: Power of accommodation (or accommodation).
Question (Year: 2017, 1 Mark): Write value of the ‘least distance of distinct vision’ for a young adult with normal vision.
- Answer: About 25 cm.
Question (Year: 2014, 1 Mark): Which part of an eye adjusts the size of its pupil?
- Answer: The Iris.
Question (Year: 2017, 3 Marks): (a) A person cannot see nearby objects, then write name of eye defect. Write name of lens used to correct this eye defect. (b) In brief define ‘Tyndall effect’.
- Answer (Part a): The defect is Hypermetropia (or Farsightedness). It is corrected using a Convex lens.
- Answer (Part b): Tyndall effect is the phenomenon of scattering of light by colloidal particles.
Question (Year: 2024, 1 Mark): The muscles of the iris controls (MCQ: Size of pupil).
- Answer: Size of pupil.
Question (Year: 2017 Supp., 3 Marks): Name two common defects of vision and type of lenses used to correct them.
- Answer: NPIS (Common defects include Myopia (Concave lens) and Hypermetropia (Convex lens)).
Question (Year: 2014, 2 Marks): Why is hypermetropia caused? How can it be corrected?
- Answer: NPIS (Hypermetropia is caused because the focal length of the eye lens is too long, or the eyeball has become too short. It is corrected by using a convex lens of appropriate power).
Question (Year: 2018, 1 Mark): What is astigmatism in human eye?
- Answer: Definition NPIS.
Question (Year: 2020, 5 Marks): What is astigmatism? How this defect is corrected?
- Answer: Astigmatism definition NPIS. It is corrected using cylindrical lenses (NPIS).
Question (Year: 2016, 1 Mark): Draw the ray diagram of an eye suffering from short sightedness (Myopia).
- Answer: Diagram NPIS (The image forms in front of the retina).
Question (Year: 2024, 1 Mark): Convex lens is useful in correcting far-sightedness. (Fill in the blank)
- Answer: Convex.
Question (Year: 2024 Supp., 1 Mark): Concave lens is useful in correcting nearsightedness. (Fill in the blank)
- Answer: Concave (NPIS, as nearsightedness/Myopia is corrected by a concave lens).
V. Atmospheric & Light Phenomena
Question (Year: 2023, 3 Marks): (i) Why do stars seem to twinkle? Explain. (ii) Why are the danger signals red in colour?
- Answer (i): Twinkling is caused by atmospheric refraction of starlight. As the light enters the Earth’s atmosphere, it undergoes continuous refraction due to varying optical densities of the air, causing the apparent position of the star to fluctuate.
- Answer (ii): Danger signals are red because red light scatters the least by fog or smoke. Red light, having the maximum wavelength, can travel the farthest distance and be seen clearly even in adverse weather conditions.
Question (Year: 2024, 1 Mark): Advance sunrise and delayed sunset are due to (MCQ: atmospheric refraction).
- Answer: Atmospheric refraction.
Question (Year: 2024 Supp., 1 Mark): Which of the following colour has the maximum wavelength – (MCQ: red).
- Answer: Red.
Question (Year: 2024 Supp., 1 Mark): The angle of deviation for the given triangular prism is (MCQ: y).
- Answer: $\mathbf{y}$ (In the given diagram, y represents the angle D, the angle of deviation).
Question (Year: 2014, 2 Marks): Why does the sky appear dark to an astronaut?
- Answer: An astronaut is outside the atmosphere where there is no medium to scatter the sunlight; hence, the sky appears dark instead of blue.
Question (Year: 2016, 2 Marks): Explain the following: (i) Atmospheric refraction and advance sunrise. (ii) Tyndall effect.
- Answer (i): Advance sunrise occurs due to atmospheric refraction which bends starlight (including the sun’s light) toward the observer, making the sun visible about two minutes before the actual sunrise.
- Answer (ii): Tyndall effect is the phenomenon of scattering of light by colloidal particles.