CBSE 2025 · Region 5 · Set 1 · Q36 · 5 marks
(A)Observe the following diagram and compare (i) speed of light and (ii) optical densities of the three media A, B and C. Also give justification for your answer of any one of the two cases in terms of refractive indices of A, B and C.
(b)Redraw the path of a ray of light through the three media, if the ray of light starting from medium A falls on the medium B(i)Obliquely and the optical density of medium B is made more than that of A and C.(ii)The ray falls normally from medium A to medium B.Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations : Observation Number Object distance (u) in cm Image distance (v) in cm $\displaystyle 1$ -$\displaystyle 15$ -$\displaystyle 60$ $\displaystyle 2$ -$\displaystyle 25$ +$\displaystyle 100$ $\displaystyle 3$ -$\displaystyle 30$ +$\displaystyle 60$ $\displaystyle 4$ -$\displaystyle 40$ +$\displaystyle 40$ $\displaystyle 5$ -$\displaystyle 60$ +$\displaystyle 30$ $\displaystyle 6$ -$\displaystyle 100$ +$\displaystyle 25$
(a)Determine the focal length of the lens. Give reason for your answer.(b)Find magnification of the image formed in Observation No. 3.(c)The numerical value of magnifications in cases of observation $\displaystyle 1$ and $\displaystyle 2$ is same. List two differences in the images formed in these two cases.
(A)
Observe the following diagram and compare (i) speed of light and (ii) optical densities of the three media A, B and C. Also give justification for your answer of any one of the two cases in terms of refractive indices of A, B and C.
(b)
Redraw the path of a ray of light through the three media, if the ray of light starting from medium A falls on the medium B
(i)
Obliquely and the optical density of medium B is made more than that of A and C.
(ii)
The ray falls normally from medium A to medium B.
Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :
| Observation Number | Object distance (u) in cm | Image distance (v) in cm |
| $\displaystyle 1$ | -$\displaystyle 15$ | -$\displaystyle 60$ |
| $\displaystyle 2$ | -$\displaystyle 25$ | +$\displaystyle 100$ |
| $\displaystyle 3$ | -$\displaystyle 30$ | +$\displaystyle 60$ |
| $\displaystyle 4$ | -$\displaystyle 40$ | +$\displaystyle 40$ |
| $\displaystyle 5$ | -$\displaystyle 60$ | +$\displaystyle 30$ |
| $\displaystyle 6$ | -$\displaystyle 100$ | +$\displaystyle 25$ |
(a)
Determine the focal length of the lens. Give reason for your answer.
(b)
Find magnification of the image formed in Observation No. 3.
(c)
The numerical value of magnifications in cases of observation $\displaystyle 1$ and $\displaystyle 2$ is same. List two differences in the images formed in these two cases.
Marking-scheme solution
(a)
(i)
Speed of light in A and B is same whereas the speed of light in C is greater than that of A and B.
(b) (i) Oblique Incidence
(ii) Normal Incidence
OR
(B) (a) \(\displaystyle 2 \mathrm{f}=40 \mathrm{~cm}\)
\[\text { ⇒ f = } 20 \text { cm }
\]
Reason: When an object is placed at 2f (- $\displaystyle 40$ cm) of a convex lens its real image formed at 2f (+ $\displaystyle 40$ cm) on the other side of the lens.
(b) \(\displaystyle \mathrm{m}=\frac{v}{u}=\frac{+60 c m}{-30 c m}=-2\)
(c) Observation No.1- image is virtual and erect Observation No. $\displaystyle 2$ - image is real and inverted
Light - Reflection and RefractionRefraction of Light and Refractive IndexAnalyselong_answerhard
More from Light - Reflection and Refraction
- (i) "In refraction of light through a rectangular glass slab, the emergent ray is always parallel to the…2025 · asked 3×
- Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when…2025 · asked 3×
- Out of the two lenses, one concave and the other convex, state which one will diverge a parallel beam of…2025 · asked 3×
- The power of a lens is -0.25 D. Based on this information, find out The type of lens and its focal length.…2025 · asked 3×
- An optical device 'X' is placed obliquely in the path of a narrow parallel beam of light. If the emergent…2025 · asked 3×
- Study the figure in which the path of a ray of light going from Medium 1 to Medium 2 is shown. Out of the two…2025 · asked 3×
- To get an image of magnification -1 on a screen using a lens of focal length 20 cm, the object distance must…2025 · asked 3×
- In order to obtain large images of the teeth of patients, the dentist holds the concave mirror in such a…2025 · asked 3×
CBSE Class 10 Science past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.