OBJECTIVE QUESTIONS FOR NEET AIIMS JIPMER www.wisedane.com

PHYSICS RAY OPTICS SET 2 MCQ’S www.wisedane.com

Q1. The focal length of a convex lens depends upon : Frequency of the light ray Wavelength of the light ray Both (A) and (B) None of these www.wisedane.com

ANSWER (C) EXPLANATION 1 𝑓 =(𝜇−1) 1 𝑅 1 − 1 𝑅 2 Refractive index ‘𝜇 ′ depends on the both wavelength and frequency of light. www.wisedane.com

Q2. A convergent lens placed inside a vessel filled with liquid is shown in the figure below. The lens has focal length +20 cm when in air, and its material has refractive index 1.5. if the liquid has refractive index 1.6, the focal length of the system is +80 cm -80 cm -160 cm -100 cm www.wisedane.com

ANSWER (C) EXPLANATION www.wisedane.com

Q3. A 1.7 m tall person stands 1.6 m in front of a vertical plane mirror. The height of his image will be : 1.6 m 1.7 m 0.85 m 3.4 m www.wisedane.com

ANSWER (B) EXPLANATION Image formed will be of the same size as object. (properties of image formed by a plane mirror). www.wisedane.com

Q4. A convergent lens is placed inside a vessel filled with liquid Q4. A convergent lens is placed inside a vessel filled with liquid. The lens has focal length +20 cm when in air, and its material has refractive index 1.5. if the liquid has refractive index 1.33, the new focal length of the lens is : + 80 cm – 80 cm –160 cm –100 cm www.wisedane.com

ANSWER (A) EXPLANATION www.wisedane.com

Q5. A plane glass slab is kept over various coloured letters Q5. A plane glass slab is kept over various coloured letters. The letter which appears least raised is : Blue Violet Green Red www.wisedane.com

ANSWER (D) EXPLANATION www.wisedane.com

Q6.The sun (diameter = D) subtends angle 𝜽 radians at the pole of a concave mirror of focal length f . The diameter of the image of the sun formed by the mirror is : f 𝜃 2f 𝜃 f2 𝜃/D D 𝜃 www.wisedane.com

ANSWER (A) EXPLANATION Since the image formed at the focus is circular and the angle subtended at the pole is 𝜃. ∴ Diameter of the image = f 𝜃. www.wisedane.com

Q7. A light beam passes from air into liquid and is deviated by 150 when the angle of incidence is 600. What is the index of refraction of the liquid ? 𝟐 𝟑 𝟑 𝟐 𝟐 𝟑 𝟑 𝟐 www.wisedane.com

ANSWER (D) EXPLANATION When the ray deviates by 15o, then, www.wisedane.com

Q8. A lens is placed between a source of light and a wall Q8. A lens is placed between a source of light and a wall. It forms images of area A1 and A2 on the wall, for its two different position. The area of source is : www.wisedane.com

ANSWER (C) EXPLANATION we have, object size www.wisedane.com

Q9. which source is associated with a line emission spectrum ? Red traffic light Sun Electric fire Neon street light www.wisedane.com

ANSWER (D) EXPLANATION Neon lights are a type of cold cathode gas-discharge light. A neon tube light is a sealed glass tube with a metal electrode at each end, filled with one of a number of gases at low pressure. A high potential of several thousand volts applied to the electrodes ionizes the gas in the tube, causing it to emit colored light. The color of the light depends on the gas in the tube. Neon lights were named for neon, a noble gas which gives off a popular orange light, but other gases and chemicals are used to produce other colors, such as hydrogen (red), helium (yellow), carbon dioxide (white), and mercury (blue). www.wisedane.com

Q10. How should people wearing their spectacles work with a microscope ? They should keep on wearing their spectacles They should take off their spectacles They may either put on their spectacles or they may take off their spectacles; it makes no difference They cannot use the microscope at all www.wisedane.com

ANSWER (b) EXPLANATION As the defect of eye can be rectified by adjusting the microscope, they should take off their spectacles. www.wisedane.com

Q11. A mark ‘A’ placed on the surface of a glass sphere is viewed through glass from a point directly opposite, Radius of sphere = 10 cm. Refractive index of glass is 1.5. Which one of the following statements is correct ? The image formed is real and at a distance of 0.4 m from the eye The image formed is virtual and at a distance of 0.2 m from the eye The image formed is virtual and at a distance 0.3 m from the centre of the sphere The image formed is real and at a distance of 0.2 m from point A www.wisedane.com

ANSWER (C) EXPLANATION www.wisedane.com

Q12. Immiscible transparent liquids A, B, C, D and E are placed in rectangular container of glass with the liquids making layers according to their densities. The refractive index of the liquids is shown in the following figure. The container is illuminated from the side and a small piece of glass having refractive index 1.61 is gently dropped into the liquid layers. The glass piece, as it descends downwards, will not be visible in (refer figure): Liquid A and B only Liquid C only Liquid D and E Liquid A, B, D and E www.wisedane.com

ANSWER (B) EXPLANATION Glass piece will not be visible in the layer having the same value of refractive index as that of glass piece i.e. the layer C www.wisedane.com

Q13. A convex lens of glass is immersed in water compared to its power in air, its power in water will : Diminish Increase Remain the same Diminish for red light and increase for blue light www.wisedane.com

ANSWER (A) EXPLANATION www.wisedane.com

Q14. The focal length of a convex lens is 30 cm and the size of the image is half of the object. The object distance is : 60 cm 90 cm 30 cm 40 cm www.wisedane.com

ANSWER (B) EXPLANATION www.wisedane.com

Q15. A lens behaves as a converging lens in air and a diverging lens in water. The refractive index of the material is - Equal to unity Equal to 1.33 Between unity and 1.33 Greater than 1.33 www.wisedane.com

ANSWER (C) EXPLANATION Between unity and 1.33, because refractive index of water is 1.33. www.wisedane.com

Q16. In the displacement method of finding focal length of a convex lens, I1 and I2 are the sizes of the images respectively for the two position of the lens. The size of the object is : www.wisedane.com

ANSWER (C) EXPLANATION 𝑂= 𝐼 1 𝐼 2 www.wisedane.com

Q17. fv and fR are the focal length of a convex lens for violet and red light, respectively, and Fv and FR are the focal length of a concave lens for violet and red light, respectively. Which one of the following relations is correct ? f v < f R and F V > F R f v > f R and F V < F R f v < f R and F V < F R f v > f R and F V > F R www.wisedane.com

ANSWER (C) EXPLANATION www.wisedane.com

Q18. A thin convex lens of focal length 30 cm and refractive index 1 Q18. A thin convex lens of focal length 30 cm and refractive index 1.5 is placed on a horizontal plane mirror. It is found that an object, at a height ‘h’ above the lens, has no parallax with its image. The h is : 60 cm 30 cm 45 cm 20 cm www.wisedane.com

ANSWER (B) EXPLANATION When rays of light are incident normal to the plane mirror, they are rebounced back. So if the object is at the focus of the convex lens, then after refraction through the lens, rays of light become normal to the plane mirror which makes them rebounce and form the image at the same point of the object. It shows height of the object is equal to focal length of the convex lens i.e. 30 cm. www.wisedane.com

Q19. Time taken by the sunlight to pass through a window of thickness 4 mm whose refractive index is 1.5 is : 2× 10 11 seconds 2× 10 8 seconds 2× 10 −11 seconds 2× 10 −8 seconds www.wisedane.com

ANSWER (C) EXPLANATION we have, μ= C air C medium ∴ C medium = C air μ Time taken= Thickness of the medium Velocity of light in the medium = Thickness ×μ C air = 4× 10 −3 ×1.5 3× 10 8 2× 10 −11 seconds www.wisedane.com

Q20. Two lenses whose powers are +2D and -4D respectively are placed in contact. The power of the combination is : – 2D – 4D + 2D + 4D www.wisedane.com

ANSWER (A) EXPLANATION 𝑃= 𝑃 1 + 𝑃 2 = +2𝐷−4𝐷 =−2𝐷 www.wisedane.com

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