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Ray optics in physics, is the study of all characteristics of light that are connected to rectilinear light propagation. Rectilinear light propagation occurs when light travels in a straight path in a homogenous medium. The study of Ray Optics employs lenses and mirrors that employ reflection and refraction concepts. Geometrical Optics is another name for this Ray optics. The feeling of sight is caused by the light type of energy.
In our daily lives, we employ a variety of optical devices that were created by combining the qualities of reflection, refraction, and dispersion
The following are some of the devices:
Multiple Choice Questions
Ques- A convex lens of focal length f = 20 cm is combined with a diverging lens of power 65 D. The power and the focal length of the combination is
(a) -1.5 D, 66.7 cm
(b) 1.5 D, 33.7 cm
(c) 5 D, 66.7 cm
(d) 5 D, 33.6 cm
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Ans - c
Given, focal length of the convex lens = f = 20 cm = 0.2 m.
Therefore, its power is: P = 1/f(in meters) = 1/0.2 = 5D.
As, the power of diverging lens is -6.5 D therefore, the power of the combination is = 5D + (-6.5 D) = -1.5 D.
The focal length of the system of lens = 1/P = 1/(-1.5 D) = -0.667 m = 66.7 cm.
Ques- The magnifying power of an astronomical telescope in normal adjustment is 100. The distance between the objective and the eyepiece is 101 cm. The focal length of the objectives and eyepiece is
(a) 10 cm and 1 cm respectively
(b) 100 cm and 1 cm respectively
(c) 1 cm and 100 cm respectively
(d) 1 cm and 10 cm respectively
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Ans- b
In normal adjustment, the object and final image are both at infinity and the separation between the objective and the eyepiece is fo + fe.
Therefore, fo + fe = 101 cm …(i)
The magnifying power of the telescope in normal adjustment is: M = -f0/fe = -100
⇒ f0 = 100fe ….(ii)
Solving the equation …(i) and …(ii), we get fo = 100 cm and fe = 1 cm.
Ques- What is the angle between the incident ray and the emergent ray in a prism called?
a) Angle of deviation
b) Angle of refraction
c) Angle of reflection
d) Angle of dispersion
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Ans - a
A prism is a transparent, homogeneous material that encloses two flat surfaces that are inclined at an angle. These are known as refracting surfaces, and the angle of deviation is the angle formed by the incident and emerging rays.
Ques- What is the difference in a deviation between any two colors called?
a) Linear dispersion
b) Angular dispersion
c) Mean deviation
d) Mean dispersion
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Ans - b
Angular dispersion is the difference in departure between any two colors.
δV-δR=(μV-μR)A is the formula for angular dispersion.
The refractive indexes for violet and red rays are μV and μR, respectively.
δ = [ δv+ δr2] is the mean deviation.
Ques- The Refractive index and wavelength are directly proportional to each other.
a) True
b) False
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Ans - b
This statement is untrue. The wavelength of color and the refractive index of the substance are inversely proportional. The wavelength of the color red, for example, is the longest, hence its refractive index is the smallest. Violet, on the other hand, has the highest refractive index and the shortest wavelength.
Ques- How much intensity of the image is increased if the diameter of the objective of a telescope is doubled?
a) Two times
b) Four times
c) Eight times
d) Sixteen times
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Ans - b
The area of the objective rises fourfold when the diameter is doubled. Its light-gathering capacity improves by fourfold. The image's brightness is also increased by four times. As a result, the image's intensity rises by a factor of four.
Ques- Two lenses of focal lengths 5 cm and 50 cm are to be used for making a telescope. Which lens will you use for the objective?
a) Both
b) Neither
c) 5 cm
d) 50 cm
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Ans - d
The objective of a telescope should have a longer focal length than the eyepiece. As a result, the objective will be a 50 cm focal length lens. As a result, the eyepiece will be the smaller of the two, namely the 5 cm focal length lens.
Ques- How many types of spherical refracting surfaces are there?
a) 2
b) 3
c) 4
d) 5
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Ans - a
A spherical refracting surface is a section of a refracting medium whose curving surface is shaped like a sphere. Convex refracting spherical surfaces and concave refracting spherical surfaces are the two forms of spherical refracting surfaces.
Ques- According to the thin lens formula, which one of the following is true regarding the focal length of the lens?
a) f is positive for concave lens
b) f is negative for convex lens
c) f is positive for a diverging lens
d) f is negative for concave lens
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Ans - d
The thin lens formula is as follows:
1/f = 1/v − 1/u
Where u is the object's distance from the lens's optical center, v is the image's distance from the lens's optical center, and f is the lens's focal length. A converging or convex lens has a positive f, whereas a diverging or concave lens has a negative f, according to the thin lens formula.
Ques- Which of the following is not a property of light?
(a) It can travel through a vacuum
(b) It has a finite speed
(c) It requires a material medium for its propagation
(d) It involves transportation energy
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Ans - c
The propagation of light waves does not require the use of a material medium. They also travel in a vacuum. A copper plate heated up when placed in the path of light beams, demonstrating that light involves energy transmission. Also, the constant speed of light is 3 108 m/s.
Ques- A convergent lens will become less convergent in :
(a) oil
(b) water
(c) both of (a) and (b)
(d) none of these
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Ans - c
Oil and water have refractive indices that are higher than the refractive index of a lens in air. As a result, in that liquid, the lens that was convex (focal length positive) in air will act as a concave lens. As a result, in both oil and water, convex lenses become less convergent.
Ques- Electromagnetic radiation belonging to................. region of the spectrum is called light.
(a) 100 nm to 400 nm
(b) 400 nm to 750 nm
(c) 750 nm to 10 nm
(d) 1000 nm to 1400 nm
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Ans - b
Radio waves, X-rays, microwaves, and gamma rays are all examples of electromagnetic (EM) radiation. Although visible light is a type of EM energy, it is just a small part of the EM spectrum, which includes a wide variety of electromagnetic wavelengths.
Ques- When light is refracted, which of the following does not change?
(a) Wavelength
(b) Frequency
(c) Velocity
(d) Amplitude
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Ans - b
When a beam of light travels from one medium to another, the physical characteristics associated with it, such as velocity, wavelength, amplitude, and so on, vary, but the frequency of the wave remains constant. As a result, the frequency of light does not change as a result of its refraction.
Ques- The apparent flattening of the sun at sunset and sunrise is due to
(a) refraction
(b) diffraction
(c) total internal reflection
(d) interference
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Ans - a
Atmospheric refraction causes the sun's disc to seem flatter during sunrise and dusk. Because the atmosphere's density and refractive index decrease with altitude, rays above and below the sun on the horizon are refracted differently.
Ques - The rays of different colors fail to converge at a point after going through a converging lens. This defect is called
(a) spherical aberration
(b) distortion
(c) coma
d) chromatic aberration
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Ans - d
Chromatic aberration is the name for this flaw. It happens because the lenses' refractive indices for different wavelengths of light are different. Because each color in the optical spectrum cannot be concentrated at a single common location, chromatic aberration emerges as "fringes" of color along borders that separate dark and bright regions of the picture.
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