Chhattisgarh State Board Class 10 Science Chapter 13 Light: Reflection & Refraction at Spherical Surfaces Exercise Multiple Choice, Fill in the Blanks, Questions and Answers here.

**Chhattisgarh State Class 10 Science Chapter 18 Solution**

**1) Choose the correct option-**

**(i) Concave lens is –**

**(a) Only diverging (b) only converging**

**(c) Neither converging nor diverging (d) Both converging & diverging.**

**Ans: – **(a) only diverging.

**(ii) If a mirror form erect image for objects placed between pole and focus, and it forms Real-Inverted image for object placed anywhere between focus and infinity, then the mirror is-**

**(a) Concave (b) convex**

**(c) Plane (d) Convex or Plane.**

**Ans: – **(a) Concave.

**(iii) The image formed by convex mirror is always-**

**(a) Smaller than object (b) Larger than object**

**(c) same sized as object (d) Real.**

**Ans: – **(a) smaller than object.

**(v) The focal length of a concave lens is 40 cm. For an object placed 40 cm away from the lens, the image will be formed at-**

**(a) Infinity (b) 40 cm from lens on the opposite side**

**(c) Behind the object (d) Between object and lens.**

**Ans: – (**d) Between object and lens.

**(vi) A lens is kept on the book and then raised by 3 cm. The text now appears erect and larger. Thefocal length of lens is-**

**(a) 3 cm (b) Less than 3 cm**

**(c) more than 3 cm (d) 1/3 cm.**

**Ans: – **(b) Less than 3 cm.

**2) Fill in the blanks:**

**(i) The image formed by convex mirror is always **virtual**………… and ………..** erect**…………., in all**

**cases. **

**(ii) To obtain a real image of same size as object, from a convex lens, the object must beplaced at ……..** twice the length of the focal length of the lens**……………………**

**(iii) The power of a lens is +5.0 D. The focal length of the lens will be ……**20cm**………. cm.**

**(iv) The focal length of a convex lens is 25 cm. The power of this lens will be ……..**0.4D**……. D.**

**3) Write down the relation between radius of curvature and focal length of a spherical mirror.**

**Ans: – **The relation between the radius of curvature (R) and the focal length (f) is f = R/2.

**4) In what type(s) of mirrors is the linear magnification less than 1, equal to 1 or greater than 1.**

**Ans: – **For the concave mirror the magnification power is different types like less than 1, equal to 1 or greater than 1.

**5) The rear-view mirrors used in vehicles are convex mirrors. Why?**

**Ans: – **The virtual, erect, diminished images are formed by the convex mirror which help to see the large images behind the traffic so convex mirror are used in rare view mirror.

**6) If image is to be obtained on a screen, what type of mirror should be used?**

**Ans: – **A real image will be obtained on screen if we use convex mirror are used.

**7) By drawing the ray diagrams for parallel incident beam of light, express what type of mirrors are converging & what type are diverging.**

**Ans: –**

**8) Define the following for spherical mirrors:**

**(i) Centre of curvature (ii) Radius of curvature (iii) Pole (iv) Aperture.**

**Ans: – **

**9) Write a note on the converging and diverging nature of lenses.**

**Ans: – **The converging and diverging nature of the lenses are seen using the convex and concave lens. If we use the convex lens in which after passing the lens the rays meet at a point which is converging in nature. For a concave lens the rays after passing the lens diverge.

**10) What is power of a lens. Write its unit.**

**Ans: – **The converging or diverging power of lens is measure as the power of the lenses. The power of lens is the equal to the 1/F or 1/focal length. And its unit is dioptre.

**12) What will be the power of a convex lens of focal length 50 cm? What if the lens is concave?**

**Ans: – **The power of the convex lens is = 1/focal length = 100/50 = +2 Dioptre.

In case of concave lens, it will be negative sign.

**13) An object is placed at 15 cm from the pole of a concave mirror of focal length 10 cm. What is the size, position, nature and magnification of the image?**

**Ans: – **The mirror formula is, 1/f = 1/v + 1/u.

Here f = focal length = -10 cm, v=? , u=-15cm.

So, v = -30 cm.

The image will be virtual and erect.

Magnification power is = v/u = -30/-15 = 2.

**17) The image of an object kept at 30 cm from the pole of a convex mirror forms at 10 cm. What is the focal length of the mirror?**

**Ans: – ** From mirror formula we came to know that, 1/f = 1/v + 1/u;

Here f =?; u = 10 cm, v =-30cm,

So, 1/ f = 1/10 -1/30 = 1/15;

Or, f = 15cm.

So, the focal length of the mirror is 15cm.

**18) The focal length of a concave mirror is 12 cm. If the object is placed at focus, where will the image be formed?**

**Ans: – **

**19) The focal length of a convex lens is 15 cm. Where should be the object placed to obtain a Real image 3 times magnified.**

**Ans: – **

**20) The focal length of a concave lens is 30 cm. What will be the position and size of the image if a 30 cm long object is placed at the focus.**

**Ans: – **

**21) For an object kept at 30 cm from a concave lens, the magnification achieved in 2/3. What is the focal length of lens?**

**Ans: – **

**24.) What is the power of a concave lens of focal length 20 cm? **

**Ans: – **Power of lens = 100/focal length.

Focal length =- 20 cm (as concave lens) ;

so, power = 100/-20 = -5D.

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