💡 Chapter 14: Light – Exercise Short Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
📖 What's Inside: This chapter covers refraction, refractive index, optical fibres, convex lens, power of lens, Snell's law and their applications. Each exercise short question is presented with the exact exam-ready answer as per the official PECTAA 2026 Physics curriculum.
📚 Related Resources – Chapter 14: Light
Light covers reflection, refraction, total internal reflection, optical fibres, lenses, prisms, dispersion, and optical instruments.
📖 Exercise Short Questions & Answers (PECTAA 2026)
14.1 What happens when light passes from air to water?
When light passes from air to water, it changes direction and bends towards the normal. This happens because light travels at different speeds in different materials.
When light passes from air to water, it changes direction and bends towards the normal. This happens because light travels at different speeds in different materials.
14.2 Define refractive index. What is the refractive index of air and water?
It is defined as the ratio of the speed of light in air or vacuum c to the speed of light in the given medium v.
\[ n = \frac{c}{v} \]
The refractive index of air is 1.00 and the refractive index of water is 1.33.
It is defined as the ratio of the speed of light in air or vacuum c to the speed of light in the given medium v.
\[ n = \frac{c}{v} \]
The refractive index of air is 1.00 and the refractive index of water is 1.33.
14.3 What is the principle behind optical fibres?
Optical fibres use the principle of Total Internal Reflection (TIR) to transmit light efficiently over long distances.
Optical fibres use the principle of Total Internal Reflection (TIR) to transmit light efficiently over long distances.
14.4 Describe briefly how a convex lens forms a real or virtual image.
A convex lens generally forms a real and inverted image when the object is placed beyond the focal point. The image is formed on the opposite side of the lens.
If the object is placed within the focal length, the lens forms a virtual and upright image.
A convex lens generally forms a real and inverted image when the object is placed beyond the focal point. The image is formed on the opposite side of the lens.
If the object is placed within the focal length, the lens forms a virtual and upright image.
14.5 How does the power of a lens relate to its focal length?
The reciprocal of focal length (f) is called power of a lens. It is given by the formula:
\[ P = \frac{1}{f} \]
The reciprocal of focal length (f) is called power of a lens. It is given by the formula:
\[ P = \frac{1}{f} \]
14.6 Write Snell's law and define the terms used in the equation.
The ratio of the sine of the angle of incidence i to the sine of the angle of refraction r remains constant for a specific pair of media.
\[ \frac{\sin i}{\sin r} = n \]
Terms defined:
i. i (Angle of incidence): The angle at which the incident light ray strikes the surface.
ii. r (Angle of refraction): The angle at which the light ray bends as it enters the new medium.
iii. n (Refractive index): The refractive index of the second medium relative to the first.
The ratio of the sine of the angle of incidence i to the sine of the angle of refraction r remains constant for a specific pair of media.
\[ \frac{\sin i}{\sin r} = n \]
Terms defined:
i. i (Angle of incidence): The angle at which the incident light ray strikes the surface.
ii. r (Angle of refraction): The angle at which the light ray bends as it enters the new medium.
iii. n (Refractive index): The refractive index of the second medium relative to the first.
📐 Key Formulas – Light
Refractive Index: \( n = \frac{c}{v} \)
Snell's Law: \( n_1 \sin i = n_2 \sin r \)
Critical Angle: \( C = \sin^{-1} \left( \frac{1}{n} \right) \)
Mirror / Lens Formula: \( \frac{1}{f} = \frac{1}{p} + \frac{1}{q} \)
Magnification: \( M = \frac{h_i}{h_o} = -\frac{q}{p} \)
Power of Lens: \( P = \frac{1}{f} \)
Unit 10Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14✨ Light
Unit 15Electrostatics
Unit 16Electricity
Unit 17Electromagnetism
Unit 18Electromagnetic Induction & EM Waves
Unit 19Electronics
Unit 20Atomic and Nuclear Physics
Unit 21Space and Environment
📖 Complete syllabus coverage for Class 10 Physics (PECTAA 2026) – Units 10 to 21
💡 Exam Tip:
For board exams, define key terms precisely, mention formulas with units, and relate to real-life examples. These exercise questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus