ICSE Selina Class 10 Physics Solutions Chapter 5: Refraction Through A Lens
Students preparing for their board exams often find optics to be one of the most visually engaging yet conceptually demanding areas of physics. If you are working through ICSE Selina Class 10 Physics Solutions, Chapter 5 on Refraction Through A Lens deserves careful attention because it connects real-world optical instruments to the mathematics of image formation. At Myclass24, the ICSE Selina Class 10 Solutions for this chapter are written with complete clarity, covering every exercise and concept so that students can revise efficiently and answer board questions with confidence.
Find the PDF of All Exercises of ICSE Selina Class 10 Physics Solutions Chapter 5: Refraction Through A Lens
Myclass24 provides a downloadable PDF covering all exercises in Chapter 5, including Exercise 5A, Exercise 5B, Exercise 5C, and the Multiple Choice Questions. Every solution includes ray diagrams, sign convention application, and stepwise numerical working in the format expected by the ICSE board. Students can save the PDF for offline revision, making it particularly useful during exam preparation when consistent practice matters most.
Key Concepts Covered in Chapter 5: Refraction Through A Lens
Chapter 5 opens with a clear distinction between convex and concave lenses. A convex lens, also called a converging lens, is thicker at the centre and thinner at the edges. It bends light rays inward, converging them at a point called the principal focus. A concave lens, on the other hand, is thinner at the centre and thicker at the edges. It diverges light rays, and the refracted rays appear to meet at a virtual focus on the same side as the incident light.
The chapter then introduces important terminology: the optical centre, principal axis, principal focus, and focal length. Students must understand that the focal length of a convex lens is positive and that of a concave lens is negative, as per the New Cartesian Sign Convention used in ICSE. This sign convention is applied consistently throughout all numerical problems and must be used correctly to avoid errors.
Image formation by lenses is explained through both ray diagrams and the lens formula. For a convex lens, the position, nature, and size of the image change depending on where the object is placed — whether beyond 2F, at 2F, between F and 2F, at F, or between the optical centre and F. Each position produces a different image, and students are expected to draw accurate ray diagrams showing at least two standard rays. For a concave lens, the image is always virtual, erect, and diminished, regardless of where the object is placed.
The lens formula, written as 1/v − 1/u = 1/f, is central to this chapter. Students must also learn to calculate magnification using m = v/u and understand what positive and negative magnification values indicate about the nature and orientation of the image. Power of a lens is another key topic — it is defined as the reciprocal of focal length in metres, measured in dioptres. A convex lens has positive power and a concave lens has negative power.
How to Draw Ray Diagrams Correctly for Chapter 5?
Ray diagrams are frequently asked in ICSE board exams and carry dedicated marks. The standard approach is to draw two of the three principal rays: one parallel to the principal axis that passes through the focus after refraction, one passing through the optical centre that continues without bending, and one directed toward the focus on the same side that emerges parallel to the principal axis after refraction.
Students often lose marks by drawing diagrams that are not to scale, not labelling the focus and optical centre, or showing incorrect direction of refracted rays. At Myclass24, the solutions for Chapter 5 include clearly labelled ray diagrams for every object position, which students can use as a direct reference while practising. The chapter also briefly discusses the human eye as a natural optical instrument, connecting lens theory to everyday biological function. This connection often appears as a short-answer question in board exams.
Why Chapter 5 Is Critical for ICSE Board Exam Scoring?
Chapter 5 carries significant weightage in the ICSE Physics board paper. Questions appear across multiple formats — definition-based short answers, ray diagram questions, and numerical problems using the lens formula and power formula. This means a student who masters this chapter thoroughly can secure marks from at least three different question types.
Numerical problems in this chapter require careful handling of signs. A single sign error in the lens formula can change the entire answer. At Myclass24, each numerical solution includes a note on which values are positive and which are negative before the substitution step, helping students internalise the sign convention rather than just memorising it. Understanding the difference between real and virtual images is also tested regularly. A real image is always formed on the opposite side of the lens from the object and can be projected on a screen. A virtual image is formed on the same side as the object and cannot be projected, only seen through the lens.