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Higher Order Thinking Skills (HOTS) Based Questions Reflection of Light

(Answers to this assignment will be uploaded separately) According to Central Board of Secondary Education (CBSE), 20% of the total marks allotted in Physics Paper (Code 042) will have questions that require higher order thinking skills. Here are few HOTS on Reflection of Light Q1. If u is object distance and v is image distance from mirror, then

(a) Plot the graph showing variation of v with u for concave mirror. (b) Plot the graph showing variation of 1/v with 1/u for concave mirror. (c) Plot the graph showing variation of v with u for convex mirror. (d) Plot the graph showing variation of 1/v with 1/u for convex mirror.

How will you determine focal length of mirror in each case (using the graph)? Q2. For concave mirror, Show analytically/algebraically and not using ray diagrams, that

(a) If an object is placed at infinity, the image will be formed at focus. (b) If an object is placed beyond curvature, then the image will be formed between F

and 2F. Also, the image will be real and diminished. (c) If an object is placed between F and 2F, then the image will be formed beyond

curvature. Also, the image will be real and enlarged. (d) If object is placed at focus, the image will be formed at infinity. (e) If object is placed at centre of curvature, the image will also be formed at centre

of curvature. (f) If object is placed between P and F, then the image formed will be virtual and

magnified. Q3. For convex mirror, Show analytically/algebraically and not using ray diagrams, that

(a) If an object is placed at infinity, the image will be formed at focus. (b) If object is placed at focus, the image will be formed at F/2. (c) If object is placed at any point in front of the mirror, then the image will always

be between P and F. Also show that image will be virtual and diminished. Q4. Two pencil beams of light are converging at a point P. A mirror is placed 12 cm before the point of convergence. Find where the image will be formed and its nature, if

(a) The mirror is concave of focal length 20 cm and (b) The mirror is convex of focal length 16 cm.

Q5. An object AB is kept in front of a concave mirror as shown in the figure.

(a) Complete the ray diagram showing the image formation of the object.

(b) How will the position and intensity of the image change if the lower half of the mirror’s reflecting surface is painted black?

Q6. A candle flame is placed in front of a large sized spherical mirror. Its image is being on a wall. The image formed on the mirror is not sharp. Explain why? How can we ensure that a sharp image be obtained on screen? Q7. A small candle, 2.5 cm in size is placed at 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Describe the nature & size of image. If the candle were moved closer to the mirror, how would the screen have to be moved?

 

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[– 54cm, – 5cm, Screen should be moved away from the mirror] Q8. Find the diameter of the image of the moon formed by a spherical concave mirror of focal length 7.6 m. The diameter of the moon is 3450 km and the distance between the earth and the moon is 3.8 x 105 km. Q9. A particle goes in a circle of radius 2cm. A concave mirror of focal length 20 cm is placed with its principal axis passing through the centre of the circle and perpendicular to its plane. The distance between the pole and the centre of the circle is 30cm. Calculate the radius of circle formed by the mirror. Q10. A mirror on the passenger side of your car is convex and has a radius of curvature with magnitude 18cm.

(a) Another car is seen in this side mirror and is 13m behind the mirror. If this car is 1.5m tall, what is the height of the image?

(b) The mirror has a warning attached that the objects viewed in it are closer than they appear. Is it true?

Q11. A man uses a concave mirror for shaving. He keeps his face at a distance of 25 cm from the mirror and gets an image which is 1.4 times enlarged. Find the focal length of the mirror. Q12. The diameter of Mars is 6794km and its minimum distance from the earth is 5.58 x 107 km. When Mars is at this distance; find the diameter of the image of mars formed by a spherical, concave telescope mirror with focal length 1.75m. Q13. The diameter of sun subtends an angle of 32’ approximately at any point on earth. Determine the position and diameter of solar image formed by a concave mirror of radius of curvature 3.5m. Q14. A thin rod of length f/3 lies along the axis of a concave mirror of focal length f. One end of its magnified image touches an end of the rod. The length of the image is Q15. A thin rod of 5 cm length is kept along the axis of a concave mirror of 10 cm focal length such that its image is real and magnified and one end touches the rod. Its magnification will be Q16. A bright source S is kept on the principal axis of a concave mirror of focal length f = 20 cm at a distance d = 30 cm from its pole. Find the distance D (in cm) in front of the concave mirror where a plane mirror should be placed so that the ray after being reflected first at the concave mirror and then by the plane mirror return to the point S.

[45 cm from concave mirror] Q17. A mobile phone is placed along the principal axis of a concave mirror. Explain why the magnification of the phone as produced by the mirror shall not be uniform and distortion will occur in the image of phone, depending on the position of the phone with respect to the mirror. Q18. An object is placed in front of a concave mirror of focal length 20 cm. The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror. [– 40/3 cm, – 80/3 cm] Q19. The image formed by a convex mirror of focal length 30 cm is a quarter of the object. What is the distance of the object from the mirror? [– 90 cm] Q20. When an object is placed at a distance of 60 cm from a convex spherical mirror, the magnification produced is 1/2. Where should the object be placed to get a magnification of 1/3? [– 120 cm] The solution to this assignment will be uploaded in few days. Visit the website www.physicswithveenus.com in a week time to check solutions to this assignment.