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Multiple choice questions on optics and refraction

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1. According to Huygens' principle, each point on a wave front acts as:

A. A point of reflection

B. A source of sound

C. A source of secondary wavelets

D. A source of primary disturbance

The correct answer is C. A source of secondary wavelets.

Explanation:
Huygens' principle states that each point on a given wave front acts as a source of new disturbances, called secondary wavelets, which spread out in all directions. The surface touching these wavelets forms the new wave front.

2. Which of the following statements correctly describes the law of reflection?

A. The angle of incidence is always greater than the angle of reflection.

B. The incident ray and reflected ray lie in different planes.

C. The angle of incidence is equal to the angle of reflection.

D. The incident ray, reflected ray, and normal are all in different planes.

The correct answer is C. The angle of incidence is equal to the angle of reflection.

Explanation:
According to the law of reflection, the angle of incidence is equal to the angle of reflection. Additionally, the incident ray, reflected ray, and the normal at the point of incidence all lie in the same plane.

3. In a plane mirror, the image formed is:

A. Real and inverted

B. Real and erect

C. Virtual and erect

D. Virtual and inverted

The correct answer is C. Virtual and erect.

Explanation:
The image formed by a plane mirror is virtual (cannot be projected on a screen), erect (upright), and appears to be the same distance behind the mirror as the object is in front.

4. The focal length of a convex mirror is:

A. Positive

B. Negative

C. Zero

D. Undefined

The correct answer is A. Positive.

Explanation:
The focal length of a concave mirror is taken as positive according to the sign convention in optics.

5. The mirror formula is given by:

A. 1/f = u + v

B. 1/f = 1/u + 1/v

C. f = u + v

D. f = u - v

The correct answer is B. 1/f = 1/u + 1/v.

Explanation:
The mirror formula relates the object distance (u), image distance (v), and focal length (f) of a spherical mirror: 1/f = 1/u + 1/v.

6. In the case of a concave mirror, the focal length is:

A. Positive

B. Negative

C. Zero

D. Undefined

The correct answer is B. Negative.

Explanation:
The focal length of a convex mirror is taken as negative according to the Cartesian sign convention.

7. A ray of light passing through the center of curvature of a concave mirror will:

A. Reflect along a different path

B. Reflect back along the same path

C. Pass through the focal point

D. Pass through the principal axis

The correct answer is B. Reflect back along the same path.

Explanation:
A ray of light passing through the center of curvature of a concave mirror reflects back along the same path, as it hits the mirror perpendicularly.

8. A virtual image is formed in a concave mirror when the object is placed:

A. At the center of curvature

B. Beyond the center of curvature

C. Between the focus and pole

D. At infinity

The correct answer is C. Between the focus and pole.

Explanation:
When an object is placed between the focus and pole of a concave mirror, it forms a virtual, upright, and magnified image.

9. Which optical phenomenon causes the apparent depth of water to be less than its actual depth?

A. Reflection

B. Dispersion

C. Refraction

D. Diffraction

The correct answer is C. Refraction.

Explanation:
Due to refraction, light rays bend when passing from water to air, making the bottom appear closer than it actually is.

10. Which type of mirror is used as a rearview mirror in vehicles?

A. Concave mirror

B. Convex mirror

C. Plane mirror

D. Spherical mirror

The correct answer is B. Convex mirror.

Explanation:
Convex mirrors are used in vehicles as rearview mirrors because they provide a wider field of view, allowing drivers to see more of the road behind them.

11. When a light ray passes obliquely from a denser to a rarer medium, it:

A. Bends towards the normal

B. Bends away from the normal

C. Does not change direction

D. Travels in a straight line

The correct answer is B. Bends away from the normal.

Explanation:
According to Snell's law, when light travels from a denser medium to a rarer medium, it bends away from the normal due to the increase in speed.

12. In a concave mirror, as an object moves from infinity towards the focal point, the image formed:

A. Moves from the focus towards infinity and becomes larger

B. Moves from infinity towards the focal point and becomes smaller

C. Moves towards the mirror and becomes inverted

D. Remains the same in size and position

The correct answer is A. Moves from the focus towards infinity and becomes larger.

Explanation:
For a concave mirror, as the object approaches the focal point from infinity, the image moves from the focus to infinity and becomes increasingly magnified.

13. Total internal reflection occurs when:

A. Light travels from a rarer to a denser medium

B. The angle of incidence exceeds the critical angle in a denser medium

C. Light reflects at any angle in a denser medium

D. Light bends at an angle of 90°

The correct answer is B. The angle of incidence exceeds the critical angle in a denser medium.

Explanation:
Total internal reflection occurs when light travels from a denser to a rarer medium, and the angle of incidence exceeds the medium's critical angle.

14. The power of a convex lens is increased when:

A. The focal length is increased

B. The focal length is decreased

C. The radius of curvature increases

D. The focal length remains unchanged

The correct answer is B. The focal length is decreased.

Explanation:
The power of a lens is inversely proportional to its focal length (P = 1/f). Decreasing the focal length increases the power of the lens.

15. The angle of deviation in a prism is minimum when:

A. Light passes parallel to the base of the prism

B. The angle of incidence is zero

C. The light ray passes symmetrically through the prism

D. Light is totally internally reflected

The correct answer is C. The light ray passes symmetrically through the prism.

Explanation:
The angle of deviation is minimum when the light ray passes through the prism symmetrically, with equal angles of incidence and emergence.

16. When two lenses of focal lengths f₁ and f₂ are placed in contact, the combined focal length (F) is given by:

A. 1/F = 1/f₁ + 1/f₂

B. F = f₁ + f₂

C. F = f₁ - f₂

D. 1/F = f₁f₂

The correct answer is A. 1/F = 1/f₁ + 1/f₂.

Explanation:
The combined focal length of two lenses in contact is given by the formula: 1/F = 1/f₁ + 1/f₂.

17. Which of the following is true for an image formed by a convex mirror?

A. The image is always virtual and smaller than the object

B. The image is real and inverted

C. The image is virtual and can be larger than the object

D. The image is real and can be larger than the object

The correct answer is A. The image is always virtual and smaller than the object.

Explanation:
Convex mirrors always produce a virtual, upright, and smaller image than the object.

18. In a microscope, the primary function of the objective lens is to:

A. Magnify the image

B. Produce a real, inverted image

C. Focus light on the retina

D. Produce a virtual, upright image

The correct answer is B. Produce a real, inverted image.

Explanation:
The objective lens in a microscope creates a real, inverted image of the object, which is then magnified by the eyepiece.

19. The power of a lens is measured in:

A. Lumens

B. Watts

C. Diopters

D. Meters

The correct answer is C. Diopters.

Explanation:
The power of a lens is defined as the reciprocal of its focal length in meters and is measured in diopters (D).

20. In the lens formula, 1/f = 1/v - 1/u, 'v' represents:

A. The image distance from the lens

B. The object distance from the lens

C. The focal length of the lens

D. The radius of curvature of the lens

The correct answer is A. The image distance from the lens.

Explanation:
In the lens formula, 1/f = 1/v - 1/u, 'v' is the image distance from the lens, while 'u' is the object distance.

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