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Questions and Answers
1.
Ratio of the speed of light in vacuum to the speed of light in medium is called
A.
Refraction
B.
Diffraction
C.
Refractive Index
D.
Interference
Correct Answer
C. Refractive Index
Explanation The ratio of the speed of light in vacuum to the speed of light in a medium is called the refractive index. Refractive index determines how much light is bent when it passes from one medium to another, such as from air to water. It is a measure of how much the speed of light is reduced in a medium compared to its speed in a vacuum.
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2.
Unit of Refractive Index:
A.
Siemen
B.
Rho
C.
Ms^{-1}
D.
No unit
Correct Answer
D. No unit
Explanation The refractive index is a dimensionless quantity that represents the ratio of the speed of light in a vacuum to the speed of light in a given medium. It is a measure of how much the speed of light is reduced when it passes through a material. Since it is a ratio, it does not have any units associated with it. Therefore, the correct answer is "no unit".
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3.
A lens of focal length 12 cm forms an erect image three times the size of object. Find distance b/w object and image.
A.
16 cm
B.
32 cm
C.
8 cm
D.
24 cm
Correct Answer
A. 16 cm
Explanation The distance between the object and the image can be determined using the lens formula 1/f = 1/v - 1/u, where f is the focal length, v is the distance of the image from the lens, and u is the distance of the object from the lens. In this case, the lens has a focal length of 12 cm and the image is three times the size of the object, indicating that the magnification is 3. By substituting the values into the formula and solving for u, we find that the distance between the object and the image is 16 cm.
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4.
Write the Lens formula : ________
Correct Answer 1/v - 1/u = 1/f
Explanation The given answer is the lens formula, which is used to calculate the focal length of a lens. It states that the inverse of the object distance (u) minus the inverse of the image distance (v) is equal to the inverse of the focal length (f). This formula is derived from the thin lens equation and is commonly used in optics to determine the characteristics of lenses and their images.
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5.
If v/u = -2 and height of object is -15 cm. Find the height of image.
A.
-30 cm
B.
+30 cm
C.
-7.5 cm
D.
+7.5 cm
Correct Answer
B. +30 cm
Explanation When the height of the object is negative (-15 cm) and the ratio of v/u is negative (-2), it indicates that the image formed is virtual and upright. The negative sign in the object's height indicates that the image is also inverted. Therefore, the height of the image would be positive and the same as the object's height, which is +30 cm.
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6.
If ray of light is parallel to principal-axis then, the ray passing through the
A.
Cf
B.
Centre of lens
C.
Focus
D.
None
Correct Answer
C. Focus
Explanation When a ray of light is parallel to the principal axis of a lens, it will pass through the focus of the lens. This is because parallel rays of light are refracted by the lens in such a way that they converge at the focal point. Therefore, the correct answer is "focus".
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7.
An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm, Find the nature.
A.
Real & inverted
B.
Virtual & erect
Correct Answer
B. Virtual & erect
Explanation When an object is placed at a distance of 4 cm from a concave lens with a focal length of 12 cm, the image formed is virtual and erect. This is because the object is placed within the focal length of the lens, causing the rays of light to diverge after passing through the lens. As a result, the image formed is virtual (cannot be projected onto a screen) and erect (upright).
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8.
Formula of power of lens :
A.
1/f(in m)
B.
100/f(in cm)
C.
1/1000f (in km)
D.
All above
Correct Answer
D. All above
Explanation The formula for the power of a lens can be expressed in different units: 1/f in meters, 100/f in centimeters, and 1/1000f in kilometers. Therefore, the correct answer is "all above" as all the given options are valid representations of the formula for the power of a lens.
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9.
A lens of short focal length has :
A.
More power
B.
Less power
C.
Moderate power
D.
None
Correct Answer
A. More power
Explanation A lens with a short focal length has more power because power is inversely proportional to focal length. A shorter focal length means that the lens can bring light rays to a focus over a shorter distance, resulting in a greater bending of the light and a stronger focusing ability. This increased bending of light allows the lens to magnify objects more effectively and produce a larger image. Therefore, a lens with a short focal length has more power compared to lenses with longer focal lengths.
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10.
Power of convex lens is negative.
A.
True
B.
False
Correct Answer
B. False
Explanation The power of a convex lens is actually positive, not negative. The power of a lens is a measure of its ability to converge or diverge light, and a convex lens is designed to converge light. It is thicker in the middle and thinner at the edges, causing light rays to converge after passing through it. Therefore, the correct answer is false.
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11.
If focal length of converging lens is 50 cm. Find the power of the lens.
A.
2 diopters
B.
4 diopters
C.
5 diopters
D.
6 diopters
Correct Answer
A. 2 diopters
12.
Unit of power of lens is ________
Correct Answer dioptre
Explanation The unit of power of a lens is dioptre. The power of a lens is a measure of its ability to converge or diverge light. It is defined as the reciprocal of the focal length of the lens in meters. The unit "dioptre" is used to represent this power and is abbreviated as "D". A positive power indicates a converging lens, while a negative power indicates a diverging lens.
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13.
Which of the following in diverging lens ?
A.
Concave lens
B.
Convex lens
Correct Answer
A. Concave lens
Explanation A diverging lens is a lens that causes parallel light rays to spread out or diverge. A concave lens is a type of diverging lens because it is thinner at the center and thicker at the edges. When light passes through a concave lens, it is bent away from the principal axis, causing the rays to spread out. On the other hand, a convex lens is thicker at the center and thinner at the edges, causing light rays to converge towards the principal axis. Therefore, the correct answer is concave lens.
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14.
Write the formula of power of combination of lenses,P =________
Correct Answer p1 + p2
Explanation The formula for the power of a combination of lenses is obtained by adding the powers of the individual lenses together. In this case, the formula is P = p1 + p2, where p1 represents the power of the first lens and p2 represents the power of the second lens. This formula allows us to calculate the overall power of the combination of lenses when they are used together.
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15.
How many types of lenses ?
A.
4
B.
3
C.
2
D.
1
Correct Answer
D. 1
Explanation The question is asking for the number of types of lenses. The correct answer is 1, indicating that there is only one type of lens.
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