Gr Xii Ray Optics Online Test 1
25 Questions 50 minutes
Questions and Answers
- 1.
Identify the device. Ans is ____________.
Explanation
A simple microscope is a type of optical instrument that uses a single lens to magnify small objects. It is used to view objects that cannot be seen with the naked eye. This device is often used in laboratories and educational settings for magnifying specimens and examining small details.Rate this question:
- 2.
Identify the phenomenon.
Explanation
The phenomenon being described here is dispersion, specifically dispersion in a prism. Dispersion refers to the separation of light into its component colors as it passes through a medium. In the case of a prism, when light enters the prism, it undergoes refraction and different wavelengths of light bend at different angles, causing the colors to separate. This phenomenon is commonly observed when white light passes through a prism and a rainbow of colors is produced.Rate this question:
- 3.
Identify the phenomenon
Explanation
The phenomenon being referred to in this question is "Mirage". A mirage is an optical illusion that occurs when light rays are bent due to the variation in air density, creating a distorted or displaced image of distant objects. This phenomenon is commonly observed in deserts or hot road surfaces, where the air near the ground is hotter than the air above it, causing the light to refract and create the illusion of water or objects appearing closer than they actually are.Rate this question:
- 4.
Identify the phenomenon
Explanation
Total internal reflection (TIR) is a phenomenon that occurs when a light ray traveling from a denser medium to a less dense medium strikes the boundary at an angle greater than the critical angle. Instead of refracting, the light ray reflects back into the denser medium. This phenomenon is commonly observed in optical fibers, where light is transmitted through the fiber by undergoing repeated total internal reflections. TIR is also responsible for the sparkle seen in diamonds, as light entering the diamond undergoes multiple internal reflections before being refracted out, creating a brilliant effect.Rate this question:
- 5.
A converging lens is used to form an image on a screen. When the upper half of the lens is covered by an opaque screen.
- A.
half the image will disappear.
- B.
Incomplete image will be formed.
- C.
Intensity of image will decrease but complete image is formed.
- D.
Intensity of image will decrease but complete image is formed.
Correct Answer
C. Intensity of image will decrease but complete image is formed.Explanation
Answer: c Explaination: (c) because focal length of lens does not change but amount of light passing through lens becomes half.Rate this question:
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- 6.
In optical fibres, the refractive index of the core is
- A.
Greater than that of the cladding.
- B.
equal to that of the cladding.
- C.
Smaller than that of the cladding.
- D.
Independent of that of cladding.
Correct Answer
A. Greater than that of the cladding.Explanation
Answer: a
Explaination: (a) R.I. of core is greater than that of the cladding for total internal reflection to occur.Rate this question:
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- 7.
An object is placed at a distance of 0.5 m in front of a plane mirror. The distance between object and image will be
- A.
0.25 m
- B.
0.5 m
- C.
1.0 m
- D.
2.0 m
Correct Answer
C. 1.0 mExplanation
Answer: c
Explaination:
(c) Distance between object and image = 0.5 + 0.5 = 1.0 mRate this question:
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- 8.
We combine two lenses, one is convex and other is concave having focal lengths f1, and f2 and their combined focal length is F. Combination of the lenses will behave like concave lens, if
- A.
f1 > f2
- B.
f1 = f2
- C.
F1 < f2.
- D.
F1 ≤ f2
Correct Answer
A. f1 > f2Explanation
Answer: a
Explaination:
(a) Focal length of the combination F=f1f2 / f1+f2, as f2 is negative so denominator f1 + f2 must be positive or f1 > f2.Rate this question:
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- 9.
Tom’ lenses of focal lengths ± 15 cm and ± 150 cm are available for making a telescope. To produce the largest magnification, the focal length of the eyepiece should be
- A.
+ 15 cm
- B.
+ 150 cm
- C.
– 150 cm
- D.
– 15 cm
Correct Answer
A. + 15 cmExplanation
Answer: A
Explaination:
(a) For telescope magnification, fe < fo to produce large magnification.Rate this question:
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- 10.
A convex lens and a concave lens, each having the same focal length of 25 cm, are put in contact to form a combination of lenses. The power of the combination (in dioptres) is
- A.
Zero
- B.
25
- C.
50
- D.
Infinity
Correct Answer
A. ZeroExplanation
Answer: A
Explaination: use P= 1 F to calculateRate this question:
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- 11.
The refractive index of the material of an equilateral prism is √3. What is the angle of minimum deviation?
- A.
45°
- B.
60°
- C.
37°
- D.
30°
Correct Answer
B. 60°Explanation
use formula to calculateRate this question:
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- 12.
The astronomical telescope consists of objective and eyepiece. The focal length of the objective is
- A.
Equal to that of the eyepiece.
- B.
Shorter than that of eyepiece.
- C.
Greater than that of eyepiece.
- D.
Five times shorter than that of eyepiece.
Correct Answer
C. Greater than that of eyepiece.Explanation
Answer: c
Explaination: (c) For producing large magnification focal length of objective is greater than that of the eyepiece.Rate this question:
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- 13.
For a total internal reflection, which of the following is correct?
- A.
Light travels from rarer to denser medium.
- B.
Light travels from denser to rarer medium.
- C.
Light travels in air only.
- D.
Light travels in water only.
Correct Answer
B. Light travels from denser to rarer medium.Explanation
When a light ray travels from a denser medium to a rarer medium, it can undergo a total internal reflection. This occurs when the angle of incidence is greater than the critical angle, causing the light to be completely reflected back into the denser medium instead of being refracted. Therefore, the correct statement is that light travels from denser to rarer medium during total internal reflection.Rate this question:
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- 14.
Which of the following forms a virtual and erect image for all positions of the object?
- A.
Concave lens
- B.
Option 2
- C.
Convex mirror
- D.
Both (a) and (c)
Correct Answer
D. Both (a) and (c)Explanation
Both a concave lens and a convex mirror form virtual and erect images for all positions of the object. A concave lens is a diverging lens that causes light rays to spread out, resulting in a virtual and erect image. A convex mirror is a diverging mirror that reflects light outwards, creating a virtual and erect image. Therefore, both options (a) and (c) are correct.Rate this question:
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- 15.
Which of the following colours of white light deviated most when passes through a prism?
- A.
Red light
- B.
Violet light
- C.
Yellow light
- D.
Both (a) and (b)
Correct Answer
B. Violet lightExplanation
Violet light deviates the most when passing through a prism because it has the shortest wavelength among the colors of white light. The shorter the wavelength, the more the light is bent or deviated when it enters a different medium, such as a prism. Therefore, violet light experiences the greatest deviation compared to the other colors of white light.Rate this question:
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- 16.
An object is immersed in a fluid. In order that the object becomes invisible, it should
- A.
Behave as a perfect reflector
- B.
Absorb all light falling on it.
- C.
Have refractive index one.
- D.
Have refractive index exactly matching with that of the surrounding fluid.
Correct Answer
D. Have refractive index exactly matching with that of the surrounding fluid.Explanation
hint: lens formulaRate this question:
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- 17.
Linear magnification, m=-1. With this information we can say that
- A.
Image is real & enlarged
- B.
Real & same size as object
- C.
Real & diminished
- D.
Virtual & same size as object
Correct Answer
B. Real & same size as objectExplanation
Based on the given information that the linear magnification (m) is -1, we can conclude that the image is real and the same size as the object. A linear magnification of -1 indicates that the image is formed on the same side as the object and is the same size as the object.Rate this question:
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- 18.
The direction of ray of light incident on a concave mirror is shown by PQ while directions in which the ray would travel after reflection is shown by four rays marked 1, 2, 3 and 4. Which of the four rays correctly shows the direction of reflected ray?
- A.
Ray 1
- B.
Ray 2
- C.
Ray 3
- D.
Ray 4
Correct Answer
B. Ray 2Explanation
Ray 2 correctly shows the direction of the reflected ray because the reflected ray always follows the law of reflection, which states that the angle of incidence is equal to the angle of reflection. In this case, ray PQ is incident on the concave mirror, and ray 2 is reflected in such a way that the angle of incidence is equal to the angle of reflection.Rate this question:
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- 19.
The optical density of turpentine is higher than that of water while its mass density is lower. Figure shows a layer of turpentine floating over water in a container. For which one of the four rays incident on turpentine in figure the path shown is correct?
- A.
Ray 1
- B.
Ray 2
- C.
Ray 3
- D.
Ray 4
Correct Answer
B. Ray 2Explanation
Ray 2 is the correct path shown for the incident ray on turpentine. This is because when light passes from a medium with a lower optical density (water) to a medium with a higher optical density (turpentine), it bends towards the normal. The path shown for Ray 2 reflects this behavior, as it bends towards the normal when entering turpentine. The other rays do not accurately depict the bending of light at the interface between the two mediums.Rate this question:
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- 20.
Consider an extended object immersed in water contained in a plane trough. When seen from close to the edge of the trough the object looks distorted. Which of the following is not correct.
- A.
The apparent depth of the points close to the edge are nearer the surface of the water compared to the points away from the edge.
- B.
The angle subtended by the image of the object at the eye is smaller than the actual angle subtended by the object in air.
- C.
Some of the points of the object far away from the edge may not be visible because of total internal reflection.
- D.
Water in a trough acts as a lens and magnifies the object.
Correct Answer
D. Water in a trough acts as a lens and magnifies the object.Explanation
The explanation for the given correct answer is that water in a trough does not act as a lens and magnify the object. When an object is immersed in water, it appears to be closer to the surface of the water compared to the points away from the edge due to refraction. The angle subtended by the image of the object at the eye is smaller than the actual angle subtended by the object in air because of this refraction. Some points of the object far away from the edge may not be visible due to total internal reflection. However, water in a trough does not have the ability to act as a lens and magnify the object.Rate this question:
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- 21.
We're standing between the focal point of a concave mirror and the mirror. What do we see? -> enlarged, upright, virtual image
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
When standing between the focal point of a concave mirror and the mirror, we see an enlarged, upright, and virtual image. This is because a concave mirror converges light rays and forms an image in front of the mirror. The image formed is larger than the object, upright (not inverted), and cannot be projected onto a screen, making it a virtual image. Therefore, the statement "enlarged, upright, virtual image" is true.Rate this question:
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- 22.
Light moves from a medium with a high index of refraction to one with a low index of refraction. The light will: -> will experience total internal reflection
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
When light moves from a medium with a high index of refraction to one with a low index of refraction, it undergoes a change in speed. This change in speed causes the light to bend away from the normal, which is the line perpendicular to the surface of the boundary between the two mediums. If the angle of incidence is greater than the critical angle, the light will be completely reflected back into the medium with the high index of refraction. This phenomenon is known as total internal reflection. Therefore, the statement "The light will experience total internal reflection" is true.Rate this question:
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- 23.
The magnification factor of an upside down image is -> either positive or negative
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The magnification factor of an upside-down image cannot be negative. The magnification factor represents the ratio of the size of the image to the size of the object. In an upside-down image, the size of the image is always smaller than the size of the object. Therefore, the magnification factor must always be positive.Rate this question:
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- 24.
The line that passes through the center of a curved mirror is called
- A.
Focal point
- B.
Principal axis
- C.
Center of curvature
- D.
Optic center
Correct Answer
B. Principal axisExplanation
The principal axis is the line that passes through the center of a curved mirror. It is an imaginary line that divides the mirror into two equal halves. This line is important in understanding the behavior of light rays as they reflect off the mirror. It helps determine the focal point, which is the point where parallel rays of light converge or appear to diverge from. The principal axis is a fundamental concept in optics and is used to analyze and predict the behavior of light in curved mirrors.Rate this question:
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- 25.
Identify the device
- A.
Compound microscope- adjusted for image at infinity
- B.
Compound microscope- adjusted for image at least distance of distinct vision
- C.
Telescope- normal adjustment
- D.
Telescope- adjusted for distinct vision
Correct Answer
B. Compound microscope- adjusted for image at least distance of distinct visionExplanation
The compound microscope is adjusted for the image at the least distance of distinct vision. This means that the microscope is set up to produce a clear and focused image when the object being observed is at the closest point at which the human eye can see it clearly without any strain. This adjustment allows for accurate and detailed examination of microscopic objects.Rate this question:
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