Excel with CBSE Class 10 Science Chapter 10 Light MCQs and Answers
FAQs on CBSE Science Chapter 10 Light MCQ Class 10
1. What types of questions are most frequently asked from Chapter 10, Light, in the CBSE Class 10 board exams for the 2025-26 session?
For the CBSE Class 10 board exam, Chapter 10 is crucial and typically features a mix of question types. Students should focus on:
- Multiple-Choice Questions (MCQs): Including assertion-reasoning questions that test conceptual clarity on topics like the nature of images.
- Short Answer Questions (2-3 marks): These often involve drawing ray diagrams for spherical mirrors and lenses, or defining key terms like principal focus and power.
- Long Answer Questions (5 marks): These are usually numerical problems based on the mirror and lens formula or questions explaining phenomena like refraction through a glass slab with a diagram.
2. Which formulas from the Light chapter are most important for solving numerical problems, and what is the typical mark allocation?
Numerical problems from this chapter are a high-scoring area. The most important formulas to master are:
- Mirror Formula: 1/v + 1/u = 1/f
- Lens Formula: 1/v - 1/u = 1/f
- Magnification for Mirrors: m = -v/u
- Magnification for Lenses: m = v/u
- Power of a Lens: P = 1/f (where f is in metres)
These numericals typically carry a weightage of 3 to 5 marks in the board exam.
3. What are some expected 3-mark important questions related to ray diagrams for concave and convex lenses?
For 3 marks, you can expect questions that require you to draw a neat, labelled ray diagram to show the image formation by a lens. Important cases include:
- An object placed at 2F₁ of a convex lens.
- An object placed between F₁ and the optical centre of a convex lens.
- Image formation by a concave lens for any position of the object.
Full marks are awarded for correctly drawn rays, arrowheads showing the direction of light, and proper labelling of F, 2F, and the object/image.
4. Why is the sign convention so critical when solving numericals for mirrors and lenses in exams?
The New Cartesian Sign Convention is critical because it ensures uniformity and correctness in calculations involving mirrors and lenses. A single mistake in applying the sign for object distance (u), image distance (v), or focal length (f) will lead to a completely incorrect result. For example, the focal length (f) for a concave mirror is always negative, while for a convex mirror it is always positive. Forgetting this rule is a common reason students lose marks in numerical problems.
5. How can you differentiate between real and virtual images to score full marks in an exam question?
To differentiate clearly between real and virtual images in your exam answers, you should state the following key points:
- Formation: A real image is formed by the actual intersection of light rays after reflection or refraction. A virtual image is formed where the rays appear to diverge from.
- Screen Projection: A real image can be projected onto a screen, whereas a virtual image cannot.
- Orientation: A real image is always inverted with respect to the object. A virtual image is always erect.
6. What kind of higher-order thinking (HOTS) questions can be expected from the laws of reflection and refraction?
Instead of just asking to state the laws, HOTS questions test their application. For example:
- Reflection: Why is a convex mirror preferred as a rear-view mirror in vehicles? The answer must connect to the fact that it provides a wider field of view and forms an erect, diminished image.
- Refraction: Why does a swimming pool appear shallower than its actual depth? This requires you to explain the phenomenon using the concept of light bending away from the normal as it travels from water (denser medium) to air (rarer medium).
7. For board exams, how is the concept of 'power of a lens' applied in multi-part important questions?
Questions on the power of a lens are often combined with the lens formula to create multi-part problems. A typical question might provide the power of two or more lenses placed in contact and ask you to find the effective power (P = P₁ + P₂) and the focal length of the combination. You might then be required to use this effective focal length in the lens formula to determine the position, nature, and size of the image for a given object.
8. What are the essential characteristics of the image formed by a concave mirror when the object is placed between the pole and the principal focus (F)?
This is a very important case for concave mirrors. When the object is placed between the pole (P) and the principal focus (F), the image formed has the following characteristics:
- Position: Behind the mirror
- Nature: Virtual and erect
- Size: Enlarged (magnified)
This is the principle used in shaving mirrors and by dentists to see a larger image of the teeth.
