Lens MCQ Quiz - Objective Question with Answer for Lens - Download Free PDF

The correct answer is Convex, concave.

Key Points

• A convex lens is thicker at the center and converges light rays to a focal point. It is also known as a converging lens.
• A concave lens is thinner at the center and diverges light rays outward. It is also called a diverging lens.
• Convex lenses are commonly used in applications such as magnifying glasses, cameras, and eyeglasses for farsightedness.
• Concave lenses are used in devices like binoculars, telescopes, and eyeglasses for nearsightedness.
• The behavior of light through these lenses is governed by the principles of refraction, where the bending of light occurs at the lens surfaces.

Additional Information

• Focal Point: The focal point is the point where light rays either converge (convex lens) or appear to diverge from (concave lens).
• Lens Formula: The relationship between the focal length (f), object distance (u), and image distance (v) is given by 1/f = 1/v - 1/u.
• Power of a Lens: The power of a lens is measured in diopters (D) and is calculated as P = 100/f, where f is the focal length in centimeters.
• Types of Lenses: Lenses are classified as convex, concave, and cylindrical, depending on their shape and function.
• Applications: Lenses play critical roles in optical instruments, including microscopes, telescopes, cameras, and corrective eyewear.

The correct answer is -37.5 cm.

Key Points

• To find the image distance (v) for an object placed at a distance (u) in front of a convex lens, we use the lens formula: 1/f = 1/v - 1/u, where f is the focal length.
• Given values: f = +25 cm (positive for convex lens), u = -15 cm (negative as the object is placed in front of the lens).
• Substitute the values in the formula: 1/25 = 1/v - 1/(-15).
• Solving the equation: 1/25 = 1/v + 1/15.
• Find a common denominator and simplify: 1/25 = (15 + 25)/(25 * 15).
• Resulting in 1/v = -1/37.5.
• Therefore, v = -37.5 cm.
• This indicates that the image is formed at a distance of 37.5 cm on the same side as the object (virtual image).

 Additional Information

• Convex Lens
  • A convex lens is a converging lens that bends light rays inward.
  • It can form both real and virtual images depending on the position of the object.
  • Convex lenses are commonly used in magnifying glasses, cameras, and corrective lenses.
• Image Formation
  • The nature of the image (real or virtual) depends on the position of the object relative to the focal length.
  • If the object is placed inside the focal length of a convex lens, the image formed is virtual, upright, and enlarged.
  • If the object is placed beyond the focal length, the image is real and inverted.

CONCEPT:

Ray Diagrams for Lenses

• A ray diagram shows the path of light rays as they pass through a lens.
• There are three primary rays used to construct a ray diagram for a thin lens:
  • Ray parallel to the principal axis: This ray refracts through the lens and passes through (or appears to pass through) the focal point on the opposite side.
  • Ray through the center of the lens: This ray passes straight through the lens without changing direction.
  • Ray through the focal point: This ray refracts through the lens and travels parallel to the principal axis.

EXPLANATION:

• For a convex lens:
  • A ray parallel to the principal axis refracts and passes through the focal point on the other side.
  • A ray passing through the center of the lens does not change direction.
  • A ray passing through the focal point refracts and travels parallel to the principal axis.

​Therefore, the correct figure representing the ray diagram is Option 3.

The correct answer is between focus F1 and optical center O.

Key Points

• The image formed by a convex lens is virtual, erect, and larger than the object when the object is placed between the focus (F1) and the optical center (O) of the lens.
• In this position, the light rays diverge after passing through the lens and appear to come from a point on the same side as the object, forming a virtual image.
• The virtual image produced is erect (upright) and magnified compared to the object.
• This scenario is typical for applications like magnifying glasses, where a larger virtual image is required.

Additional Information

• Convex Lens
  • A convex lens is thicker at the center than at the edges.
  • It converges light rays that pass through it, focusing them to a point known as the focal point (F1).
  • Convex lenses are also known as converging lenses.
• Virtual Image
  • A virtual image cannot be projected on a screen as it forms on the same side as the object.
  • It is formed by the apparent divergence of rays from a common point.
• Optical Center (O)
  • The optical center is a point on the lens through which light passes without being refracted.
  • It is the geometrical center of the lens.
• Magnification
  • Magnification refers to the process of enlarging the appearance of an object through optical instruments.
  • In lenses, magnification is determined by the ratio of the image distance to the object distance.

The correct answer is 7.5 cm; virtual.

Key Points

• The power of the lens is -10.0 D, which indicates it is a diverging lens.
• The formula for the focal length (f) of a lens is given by f = 1/P, where P is the power. Thus, f = -0.1 m or -10 cm.
• Using the lens formula (1/f = 1/v - 1/u), where u is the object distance (in this case, -30 cm), we can find the image distance (v).
• Substituting the given values, we get 1/(-10) = 1/v - 1/(-30). Solving this gives v = -7.5 cm, indicating the image is virtual.
• Thus, the image is formed at a distance of 7.5 cm from the lens and is virtual.

Additional Information

• Lens Power
  • The power of a lens is measured in diopters (D), and it is the reciprocal of the focal length in meters.
  • A positive power indicates a converging lens, while a negative power indicates a diverging lens.
• Lens Formula
  • The lens formula is 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance.
  • This formula helps in determining the position and nature (real or virtual) of the image formed by the lens.
• Virtual Image
  • A virtual image is formed when the outgoing rays from a point on the object appear to diverge from a point behind the lens.
  • Virtual images cannot be projected on a screen as they are formed by diverging rays.
• Diverging Lens
  • A diverging lens spreads out light rays that are initially parallel, causing them to diverge away from a common point.
  • These lenses are thinner at the center and thicker at the edges.

Concept:

Power of Lens: 

1. The inverse of the focal length is known as the power of the lens.

2. It shows the bending strength for the light ray of the lens.

3. The unit of power of a lens is Dioptre when the focal length of the lens is taken in meter (m).

\(P = \frac{1}{f}\)

where,

P is the power of the lens and f is the focal length of the lens.

​Calculation:

Given - The power of a concave lens is -0.5 D

The power of a convex lens (P) is 

\(f=\frac{1}{D}=\frac{1}{-0.5}\)

f = -2m

Important Points

Concave lens: 

• It is a diverging lens that diverges the parallel beam of light.
• It can also gather light from all directions and project it as a parallel beam.
• The focal length of the concave lens is negative.
• It has a virtual focus from the diverging rays of light that seem to converge.

Convex lens:

• The lens whose refracting surface is upside is called a convex lens.
• The convex lens is also called a converging lens.
• The focal length of a convex lens is positive.

The correct answer is option 1)12cm

Given:

of a lens whose power is +5.0 D.

Formula:

Power of lens:

len formula:

Calculations:

\(P={1\over f}\)

\(f={1\over P}={1\over5}=0.2m=20cm\)

\({1\over f}={1\over v}-{1\over u}\)

\({1\over 20}={1\over v}-{1\over -10}\)

\({1\over v}={1\over 20}+{1\over -10}={1-2\over20}\)

\(v={-20\over 1}=-20cm\)

We know that, the magnification of the lens:

\(m={di\over do}={v\over u}\)

\({di\over 6}={-20\over -10}=2\)

\(di=6*2=12cm\)

Therefore, the diameter of the image is 12cm.

The correct answer is real, inverted and enlarged.

Key Points

•  Magnification of a mirror or a lens is the ratio of the size of the image formed by the mirror or the lens and the size of the object.
• If the magnification is more than 1, the image is magnified and smaller and if it is less than 1 then it is diminished and enlarged.
• If the magnification is positive the image formed is erect and virtual and if it is negative the image formed is real and inverted.
• Here the magnification is -1.38 which is less than 1 so the image is diminished and enlarged , as the value is negative the image formed is real and inverted.
• So the image formed is real, inverted and enlarged.

The correct answer is m = -1.Key Points

• When an object is placed at a distance of 2f from a convex lens, the image is formed at a distance of 2f on the other side of the lens.
• The image formed is real, inverted, and of the same size as the object.
• Magnification (m) = Height of Image / Height of Object = -1 (negative sign indicates inversion).
• This scenario is a standard case in lens formulas and ray diagrams of convex lenses.
• Thus, magnification 'm' = -1 for object placed at 2f in convex lens.

Additional Information

• Convex Lens (Converging Lens)
  • A convex lens is thicker at the center and converges parallel rays of light to a point called the focus.
  • It forms real and inverted images for object distances greater than focal length (f), and virtual, erect images when the object is within f.
• Magnification (m)
  • Magnification = v/u or Height of Image / Height of Object.
  • Positive magnification indicates an erect image, negative indicates an inverted image.
• Lens Formula
  • 1/f = 1/v - 1/u where f = focal length, v = image distance, u = object distance.
  • All distances are measured from the optical center of the lens.
• Applications of Convex Lens
  • Used in magnifying glasses, microscopes, cameras, and human eye correction.

The correct answer is real and diminished.

Key Points

•  A convex lens is thicker at the center than at the edges.
•  It is called a converging lens because the rays of light that pass through it are brought closer together (they converge).
•  When parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.
• The distance between the principal focus and the center of the lens is called the focal length.
• The ray diagram 

​

Additional Information

• ​ The image formed in the convex lens become real and enlarged when the object is placed upside down between optical centre and focal length.
• The convex lens always form virtual and dimiished image irrespective of the position.
• The convex lens form virtual and enlarged image when the object is between focus and lens.

The correct answer is -37.5 cm.

Key Points

• To find the image distance (v) for an object placed at a distance (u) in front of a convex lens, we use the lens formula: 1/f = 1/v - 1/u, where f is the focal length.
• Given values: f = +25 cm (positive for convex lens), u = -15 cm (negative as the object is placed in front of the lens).
• Substitute the values in the formula: 1/25 = 1/v - 1/(-15).
• Solving the equation: 1/25 = 1/v + 1/15.
• Find a common denominator and simplify: 1/25 = (15 + 25)/(25 * 15).
• Resulting in 1/v = -1/37.5.
• Therefore, v = -37.5 cm.
• This indicates that the image is formed at a distance of 37.5 cm on the same side as the object (virtual image).

 Additional Information

• Convex Lens
  • A convex lens is a converging lens that bends light rays inward.
  • It can form both real and virtual images depending on the position of the object.
  • Convex lenses are commonly used in magnifying glasses, cameras, and corrective lenses.
• Image Formation
  • The nature of the image (real or virtual) depends on the position of the object relative to the focal length.
  • If the object is placed inside the focal length of a convex lens, the image formed is virtual, upright, and enlarged.
  • If the object is placed beyond the focal length, the image is real and inverted.

CONCEPT:

Ray Diagrams for Lenses

• A ray diagram shows the path of light rays as they pass through a lens.
• There are three primary rays used to construct a ray diagram for a thin lens:
  • Ray parallel to the principal axis: This ray refracts through the lens and passes through (or appears to pass through) the focal point on the opposite side.
  • Ray through the center of the lens: This ray passes straight through the lens without changing direction.
  • Ray through the focal point: This ray refracts through the lens and travels parallel to the principal axis.

EXPLANATION:

• For a convex lens:
  • A ray parallel to the principal axis refracts and passes through the focal point on the other side.
  • A ray passing through the center of the lens does not change direction.
  • A ray passing through the focal point refracts and travels parallel to the principal axis.

​Therefore, the correct figure representing the ray diagram is Option 3.

The correct answer is between focus F1 and optical center O.

Key Points

• The image formed by a convex lens is virtual, erect, and larger than the object when the object is placed between the focus (F1) and the optical center (O) of the lens.
• In this position, the light rays diverge after passing through the lens and appear to come from a point on the same side as the object, forming a virtual image.
• The virtual image produced is erect (upright) and magnified compared to the object.
• This scenario is typical for applications like magnifying glasses, where a larger virtual image is required.

Additional Information

• Convex Lens
  • A convex lens is thicker at the center than at the edges.
  • It converges light rays that pass through it, focusing them to a point known as the focal point (F1).
  • Convex lenses are also known as converging lenses.
• Virtual Image
  • A virtual image cannot be projected on a screen as it forms on the same side as the object.
  • It is formed by the apparent divergence of rays from a common point.
• Optical Center (O)
  • The optical center is a point on the lens through which light passes without being refracted.
  • It is the geometrical center of the lens.
• Magnification
  • Magnification refers to the process of enlarging the appearance of an object through optical instruments.
  • In lenses, magnification is determined by the ratio of the image distance to the object distance.

The correct answer is 7.5 cm; virtual.

Key Points

• The power of the lens is -10.0 D, which indicates it is a diverging lens.
• The formula for the focal length (f) of a lens is given by f = 1/P, where P is the power. Thus, f = -0.1 m or -10 cm.
• Using the lens formula (1/f = 1/v - 1/u), where u is the object distance (in this case, -30 cm), we can find the image distance (v).
• Substituting the given values, we get 1/(-10) = 1/v - 1/(-30). Solving this gives v = -7.5 cm, indicating the image is virtual.
• Thus, the image is formed at a distance of 7.5 cm from the lens and is virtual.

Additional Information

• Lens Power
  • The power of a lens is measured in diopters (D), and it is the reciprocal of the focal length in meters.
  • A positive power indicates a converging lens, while a negative power indicates a diverging lens.
• Lens Formula
  • The lens formula is 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance.
  • This formula helps in determining the position and nature (real or virtual) of the image formed by the lens.
• Virtual Image
  • A virtual image is formed when the outgoing rays from a point on the object appear to diverge from a point behind the lens.
  • Virtual images cannot be projected on a screen as they are formed by diverging rays.
• Diverging Lens
  • A diverging lens spreads out light rays that are initially parallel, causing them to diverge away from a common point.
  • These lenses are thinner at the center and thicker at the edges.

Concept:

Power of Lens: 

1. The inverse of the focal length is known as the power of the lens.

2. It shows the bending strength for the light ray of the lens.

3. The unit of power of a lens is Dioptre when the focal length of the lens is taken in meter (m).

\(P = \frac{1}{f}\)

where,

P is the power of the lens and f is the focal length of the lens.

​Calculation:

Given - The power of a concave lens is -0.5 D

The power of a convex lens (P) is 

\(f=\frac{1}{D}=\frac{1}{-0.5}\)

f = -2m

Important Points

Concave lens: 

• It is a diverging lens that diverges the parallel beam of light.
• It can also gather light from all directions and project it as a parallel beam.
• The focal length of the concave lens is negative.
• It has a virtual focus from the diverging rays of light that seem to converge.

Convex lens:

• The lens whose refracting surface is upside is called a convex lens.
• The convex lens is also called a converging lens.
• The focal length of a convex lens is positive.