UET UG Physics Booster Test 2 -Lens Combinations and Prisms -

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CUET UG Physics Booster Test 2 -Lens Combinations and Prisms

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Physics Booster Test 2 -Lens Combinations and Prisms

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QUESTION 1 OF 20

What is the effective focal length of a combination of a convex lens of focal length 30 cm and a concave lens of focal length 20 cm in contact?

Answer Review

1 What is the effective focal length of a combination of a convex lens of focal length 30 cm and a concave lens of focal length 20 cm in contact?

A 10 cm

B 60 cm

C -60 cm

D -10 cm

💡 Short Explanation

�� For lenses in contact: 1/f = 1/f₁ + 1/f₂ �� Convex lens: f₁ = +30 cm �� Concave lens: f₂ = -20 cm

✅ Correct Answer Explanation

1/f = 1/30 + 1/(-20) 1/f = (2 - 3)/60 1/f = -1/60 f = -60 cm Hence, the effective focal length is -60 cm.

❓ Why Other Options Are Incorrect

�� A: Incorrect calculation.
�� B: Sign should be negative.
�� D: Incorrect value.

🎯 Strategy

Used

Lens Combination Formula

🧠 Memory Trick

"Add reciprocals, not focal lengths."

📚 Class XII Physics – Ray Optics and Optical Instruments – Combination of Thin Lenses

2 A lens combination consists of a convex lens of focal length 50 cm and a concave lens of focal length 25 cm. What is the net power of this combination?

A -2.0 D

B +2.0 D

C -6.0 D

D +6.0 D

💡 Short Explanation

�� Power P = 1/f (in metres) �� Net power = algebraic sum of powers.

✅ Correct Answer Explanation

Convex lens: P₁ = 1/0.5 = +2 D Concave lens: P₂ = 1/(-0.25) = -4 D Net power: P = P₁ + P₂ P = 2 - 4 P = -2 D Hence Option A is correct.

❓ Why Other Options Are Incorrect

�� B: Sign incorrect.
�� C: Wrong calculation.
�� D: Wrong calculation.

🎯 Strategy

Used

Power Addition Rule

🧠 Memory Trick

"Lens powers add algebraically."

📚 Class XII Physics – Ray Optics and Optical Instruments – Power of Lens Combination

3 The use of multi-component lenses in the objective and eyepiece of modern optical microscopes:

A increases the tube length of the instrument unnecessarily

B improves image quality by minimizing various optical aberrations

C restricts the focal plane, causing image blurring

D inverts the final image again to make it erect without affecting sharpness

💡 Short Explanation

�� Multiple lenses reduce defects. �� Improves sharpness and clarity. �� Reduces aberrations.

✅ Correct Answer Explanation

Modern microscopes use lens combinations to reduce: • Spherical aberration • Chromatic aberration This improves image quality and sharpness. Hence Option B is correct.

❓ Why Other Options Are Incorrect

�� A: Not the primary purpose.
�� C: Opposite effect.
�� D: Not the objective.

🎯 Strategy

Used

Concept Recall

🧠 Memory Trick

"More lenses → Fewer aberrations."

📚 Class XII Physics – Optical Instruments

4 If a two-lens system consists of a first lens forming an image that serves as the object for the second lens, and their individual magnifications are m₁ and m₂, the total magnification m of the combination is:

A m₁ + m₂

B m₁ / m₂

C m₁ × m₂

D |m₁ - m₂|

💡 Short Explanation

�� Total magnification is the product of individual magnifications.

✅ Correct Answer Explanation

For a lens combination: m = m₁ × m₂ The image formed by the first lens acts as the object for the second lens. Hence Option C is correct.

❓ Why Other Options Are Incorrect

�� A: Magnifications do not add.
�� B: No such relation.
�� D: Not a valid formula.

🎯 Strategy

Used

Formula Recall

🧠 Memory Trick

"Magnifications multiply."

📚 Class XII Physics – Lens Combinations

5 Prism incidence geometry statements:
1. For any given angle of deviation (except minimum), there are two values of the angle of incidence.
2. The angle of incidence is measured with respect to the tangent of the prism surface.
3. At minimum deviation, the angle of incidence equals the angle of emergence.
4. The path of the ray can be traced back, yielding the same angle of deviation.

A 1, 3, 4

B 2, 3, 4

C 1, 2, 4

D 1, 2, 3

💡 Short Explanation

�� Incidence is measured from the normal. �� Minimum deviation gives symmetry.

✅ Correct Answer Explanation

Statement 1 Two incidence angles correspond to the same deviation except at minimum deviation. Statement 2 Angle of incidence is measured from the normal, not tangent. Statement 3 At minimum deviation: i = e Statement 4 Light path is reversible. Hence Option A is correct.

❓ Why Other Options Are Incorrect

All contain incorrect Statement 2.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

"At minimum deviation: i = e."

📚 Class XII Physics – Prism Geometry

6 In a triangular prism, if the angle of incidence i is altered from a specific value:

A the deviation angle δ decreases continuously for all values of i

B for a given deviation angle δ (other than the minimum), the emergent ray can have two possible angles corresponding to interchanging i and e

C the emergent ray is always parallel to the incident ray

D the angle of emergence remains constant regardless of the incidence angle

💡 Short Explanation

�� Prism deviation curve is symmetric. �� Same deviation can occur for two ray paths.

✅ Correct Answer Explanation

For a given deviation (except minimum), (i, e) and (e, i) produce the same deviation. Hence Option B is correct.

❓ Why Other Options Are Incorrect

�� A: Deviation first decreases then increases.
�� C: Not true for prisms.
�� D: Emergence changes with incidence.

🎯 Strategy

Used

Prism Deviation Concept

🧠 Memory Trick

"Same deviation ↔ interchange i and e."

📚 Class XII Physics – Prism

7 Match List I with List II.

List I	List II
1. Dₘ	a. Angle of minimum deviation
2. δ	b. i + e − A
3. A	c. Refracting angle of prism
4. r₁ + r₂	d. Equals prism angle A

A 1-a, 2-b, 3-c, 4-d

B 1-b, 2-a, 3-d, 4-c

C 1-a, 2-b, 3-d, 4-c

D 1-a, 2-c, 3-b, 4-d

💡 Short Explanation

�� Dₘ → Angle of minimum deviation �� δ = i + e − A �� A → Refracting angle of prism �� r₁ + r₂ = A

✅ Correct Answer Explanation

1 → a (Angle of minimum deviation) 2 → b (i + e − A) 3 → c (Refracting angle of prism) 4 → d (Equals prism angle A) Therefore: 1-a, 2-b, 3-c, 4-d Hence Option A is correct.

❓ Why Other Options Are Incorrect

�� B: Incorrect matching of Dₘ, δ, A and r₁ + r₂.
�� C: Incorrect matching of A and r₁ + r₂.
�� D: Incorrect matching of δ and A.

🎯 Strategy

Used

Direct Matching

🧠 Memory Trick

"Dₘ → minimum deviation, δ → i + e − A, r₁ + r₂ = A"

📚 Class XII Physics – Ray Optics and Optical Instruments – Prism Relations

8 Identify the incorrect statement about the geometry of prismatic deviation:

A The sum of the refraction angles r₁ and r₂ is equal to the refracting angle A of the prism.

B In quadrilateral AQNR, the sum of the vertex angle A and angle ∠QNR is 180°.

C The total deviation δ is the product of deviations at the two individual faces.

D The total deviation δ depends on the angle of incidence.

💡 Short Explanation

�� Deviations add, not multiply.

✅ Correct Answer Explanation

Total deviation: δ = (i - r₁) + (e - r₂) The deviations are summed. Hence Option C is incorrect.

❓ Why Other Options Are Incorrect

�� A: Correct.
�� B: Correct geometric relation.
�� D: Correct.

🎯 Strategy

Used

Formula Recall

🧠 Memory Trick

"Deviation adds."

📚 Class XII Physics – Prism Deviation

9 At the exact position of minimum deviation in a symmetric glass prism, the refracted ray inside the prism is ____________ to its base, and the internal angles of refraction at the two surfaces are ____________.

A Perpendicular, Unequal

B Parallel, Equal

C Parallel, Unequal

D Oblique, Equal

💡 Short Explanation

�� Minimum deviation condition is symmetric.

✅ Correct Answer Explanation

At minimum deviation: i = e r₁ = r₂ = A/2 The refracted ray becomes parallel to the prism base. Hence Option B is correct.

❓ Why Other Options Are Incorrect

They violate minimum deviation symmetry.

🎯 Strategy

Used

Concept Recall

🧠 Memory Trick

"Minimum deviation → Perfect symmetry."

📚 Class XII Physics – Minimum Deviation

10 A beam of light is incident on an equilateral glass prism (A = 60°). If the prism produces a minimum deviation of 30°, what is the required angle of incidence?

A 30°

B 45°

C 60°

D 90°

💡 Short Explanation

At minimum deviation: i = e Dₘ = 2i - A

✅ Correct Answer Explanation

Dₘ = 2i - A 30 = 2i - 60 2i = 90 i = 45° Hence Option B is correct.

❓ Why Other Options Are Incorrect

�� A: Too small.
�� C: Gives different deviation.
�� D: Impossible.

🎯 Strategy

Used

Minimum Deviation Formula

🧠 Memory Trick

"Dₘ = 2i - A"

📚 Class XII Physics – Prism at Minimum Deviation

11 For a prism of angle A and minimum deviation Dₘ, the refractive index n₂₁ of the prism material with respect to the surrounding medium is given by:

A sin((A + Dₘ)/2) / sin(A/2)

B sin(A/2) / sin((A + Dₘ)/2)

C sin(A + Dₘ) / sin(A)

D sin(A) / sin(A + Dₘ)

💡 Short Explanation

�� Refractive index of a prism is determined using prism angle and minimum deviation.

✅ Correct Answer Explanation

At minimum deviation: i = e r₁ = r₂ = A/2 Using Snell's law: n₂₁ = sin((A + Dₘ)/2) / sin(A/2) Hence Option A is correct.

❓ Why Other Options Are Incorrect

�� B: Reciprocal form.
�� C: Not the prism formula.
�� D: Incorrect relation.

🎯 Strategy

Used

Direct Formula Recall

🧠 Memory Trick

"Top = (A + Dₘ)/2, Bottom = A/2"

📚 Class XII Physics – Prism Refractive Index

12 Consider the statements regarding the prism experimental setup. Choose the correct statements:
1. The angle of minimum deviation Dₘ must be measured.
2. The refracting angle A of the prism must be measured.
3. The prism must be extremely thin to measure the index properly.
4. The formula requires measuring both A and Dₘ experimentally.

A 1 and 2 only

B 3 and 4 only

C 1, 2, and 3

D 1, 2, and 4

💡 Short Explanation

�� Both prism angle and minimum deviation are required.

✅ Correct Answer Explanation

Statement 1 Minimum deviation must be measured. Statement 2 Prism angle A must be measured. Statement 3 A prism need not be extremely thin. Statement 4 Both A and Dₘ are needed in: n₂₁ = sin((A + Dₘ)/2) / sin(A/2) Hence Option D is correct.

❓ Why Other Options Are Incorrect

They either omit a correct statement or include Statement 3.

🎯 Strategy

Used

Statement Analysis

🧠 Memory Trick

"Measure A and Dₘ → Find n"

📚 Class XII Physics – Experimental Determination of Refractive Index

13 A thin glass prism has a refracting angle of 4° and is made of material with a relative refractive index of 1.5. Using the thin prism approximation, what is the angle of minimum deviation?

A 1.0°

B 2.0°

C 4.0°

D 6.0°

💡 Short Explanation

For a thin prism: Dₘ = (n₂₁ − 1)A

✅ Correct Answer Explanation

Dₘ = (1.5 − 1) × 4° Dₘ = 0.5 × 4° Dₘ = 2° Hence Option B is correct.

❓ Why Other Options Are Incorrect

�� A: Half the correct value.
�� C: Equal to prism angle.
�� D: Too large.

🎯 Strategy

Used

Thin Prism Formula

🧠 Memory Trick

"Dₘ = (n − 1)A"

📚 Class XII Physics – Thin Prism

14 In practical optical systems utilizing thin prisms:

A the deviation produced is extremely large for any angle of incidence

B the minimum deviation is solely dependent on the refractive index and independent of the prism angle

C they do not deviate light much, relying on the small angle approximation

D total internal reflection always occurs at the second surface

💡 Short Explanation

�� Thin prisms have small refracting angles. �� Hence deviation is small.

✅ Correct Answer Explanation

Thin prisms satisfy: A ≪ 1 Dₘ = (n₂₁ − 1)A Therefore deviation remains small and small-angle approximations apply. Hence Option C is correct.

❓ Why Other Options Are Incorrect

�� A: Opposite of thin prism behavior.
�� B: Depends on both n and A.
�� D: Not necessarily true.

🎯 Strategy

Used

Concept Application

🧠 Memory Trick

"Thin prism → Small deviation"

📚 Class XII Physics – Thin Prism Approximation

15 Identify the incorrect statement about light interaction with optical materials:

A Monochromatic light produces the identical perception of colors on an object as white light.

B Thick lenses can give colored images due to material dispersion.

C Dispersion is the splitting of light into its constituent colors by the material.

D The optical density of a medium dictates how a ray bends relative to the normal.

💡 Short Explanation

�� Color perception changes under monochromatic light.

✅ Correct Answer Explanation

Objects appear differently under monochromatic illumination because only one wavelength is present. Hence Option A is incorrect.

❓ Why Other Options Are Incorrect

�� B: Correct.
�� C: Correct definition of dispersion.
�� D: Correct.

🎯 Strategy

Used

Concept Recall

🧠 Memory Trick

"No white light → No natural colors"

📚 Class XII Physics – Dispersion and Color

16 If the normal to a spherical reflecting or refracting surface is drawn at the exact point of incidence, this normal geometrically represents the line joining the ____________ of the interface to the point of incidence.

A Principal focus

B Pole

C Centre of curvature

D Infinite axis

💡 Short Explanation

�� Normal on a spherical surface passes through its centre.

✅ Correct Answer Explanation

For any spherical surface, the radius drawn to the point of incidence acts as the normal. Therefore it passes through the centre of curvature. Hence Option C is correct.

❓ Why Other Options Are Incorrect

�� A: Focus is different.
�� B: Pole is not generally the normal.
�� D: No such concept.

🎯 Strategy

Used

Geometrical Optics Concept

🧠 Memory Trick

"Radius = Normal"

📚 Class XII Physics – Spherical Refraction

17 Choose the correct statements about the function of a screen in viewing a real image:
1. The screen physically converges the rays to form the image point.
2. The screen diffuses the rays converging at an image point in space.
3. Without the screen, the image still technically exists suspended in space.
4. The screen alters the focal length of the imaging lens.

A 2 and 3

B 1 and 4

C 2 and 4

D 1, 2, and 3

💡 Short Explanation

�� Screen only makes the image visible.

✅ Correct Answer Explanation

Statement 1 Screen does not form the image. Statement 2 Screen diffuses light. Statement 3 Image exists even without screen. Statement 4 Screen does not affect focal length. Hence Option A is correct.

❓ Why Other Options Are Incorrect

They include incorrect Statements 1 or 4.

🎯 Strategy

Used

Concept Analysis

🧠 Memory Trick

"Screen shows, not forms."

📚 Class XII Physics – Real Images

18 A real image formed by a convex lens is viewed on a screen. If the screen is abruptly removed:

A the image is instantly destroyed as light rays stop converging

B the light rays are forced to reflect back towards the lens

C the image point still exists in space where the rays converge and then diverge

D the image transforms completely into a virtual image

💡 Short Explanation

�� Real image formation is independent of the screen.

✅ Correct Answer Explanation

The rays still meet at the image point and then diverge. Removing the screen only removes the visible projection. Hence Option C is correct.

❓ Why Other Options Are Incorrect

�� A: Rays continue to converge.
�� B: No reflection occurs.
�� D: Real image remains real.

🎯 Strategy

Used

Image Formation Concept

🧠 Memory Trick

"Screen removed ≠ Image removed"

📚 Class XII Physics – Real Images

19 Match List I with List II.

List I	List II
1. Dispersion	a. Brilliance of diamond / Optical fibres
2. Total Internal Reflection	b. Splitting of white light
3. Refraction	c. Ray inside prism parallel to base
4. Minimum Deviation	d. Bending at interface

A 1-b, 2-a, 3-d, 4-c

B 1-a, 2-b, 3-c, 4-d

C 1-b, 2-c, 3-d, 4-a

D 1-d, 2-a, 3-b, 4-c

💡 Short Explanation

�� Dispersion → Splitting of white light �� Total Internal Reflection → Brilliance of diamond / Optical fibres �� Refraction → Bending at interface �� Minimum Deviation → Ray inside prism parallel to base

✅ Correct Answer Explanation

1 → b (Splitting of white light) • Dispersion is the phenomenon in which white light splits into its constituent colours. 2 → a (Brilliance of diamond / Optical fibres) • Total Internal Reflection is responsible for the brilliance of diamonds and the working of optical fibres. 3 → d (Bending at interface) • Refraction is the bending of light when it passes from one medium to another. 4 → c (Ray inside prism parallel to base) • At the position of minimum deviation, the refracted ray inside the prism becomes parallel to the base of the prism. Therefore: 1-b, 2-a, 3-d, 4-c Hence Option A is correct.

❓ Why Other Options Are Incorrect

�� B: Incorrect matching of Dispersion and Total Internal Reflection.
�� C: Incorrect matching of Total Internal Reflection and Minimum Deviation.
�� D: Incorrect matching of Dispersion and Refraction.

🎯 Strategy

Used

Direct Matching

🧠 Memory Trick

"Dispersion splits, TIR shines, Refraction bends, Minimum deviation aligns."

📚 Class XII Physics – Ray Optics and Optical Instruments – Dispersion and Total Internal Reflection

20 Lenses of large diameters and thickness often suffer from optical defects. Because of dispersion, they can produce ____________ images, a defect that prevents a purely ____________ focus.

A Sharp, Spherical

B Coloured, Monochromatic

C Inverted, Diminished

D Diffused, Geometric

💡 Short Explanation

�� Dispersion causes chromatic aberration.

✅ Correct Answer Explanation

Different wavelengths focus at different points. This produces coloured images and prevents a single monochromatic focus. Hence Option B is correct.

❓ Why Other Options Are Incorrect

�� A: Opposite effect.
�� C: Not due to dispersion.
�� D: Not the standard defect.

🎯 Strategy

Used

Concept Recall

🧠 Memory Trick

"Dispersion → Color Fringes"

📚 Class XII Physics – Dispersion and Lens Aberrations

CUET UG Physics Booster Test 2 -Lens Combinations and Prisms

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