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Tamil Nadu Board 12th Standard Physics - Unit 6: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 6 from the Tamil Nadu State Board 12th Standard Physics textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Unit 6 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 12 students! Prepare well and aim for top scores. Thank you!

I. Multiple choice questions.

1. The speed of light in an isotropic medium depends on,
(a) its intensity
(b) its wavelength
(c) the nature of propagation
(d) the motion of the source

Answer Key:

(b) its wavelength 

2. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the

image is,

(a) 2.5 cm 

(b) 5cm

(c) 10 cm 

(d) 15cm

Answer Key: 

(b) 5cm

 

3. An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified.
(a) 2f and c 

(b) c and ∞
(c) f and O 

(d) None of these

Answer Key:

(d) None of these 

  
4. For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is,
(a) ${\mathbf{30}}^{\mathbf{°}}$ 

(b) ${\mathbf{45}}^{\mathbf{°}}$
(c) ${\mathbf{60}}^{\mathbf{°}}$ 

(d) ${\mathbf{90}}^{\mathbf{°}}$

Answer Key:

(a) ${\mathbf{30}}^{\mathbf{°}}$  

  
5. If the velocity and wavelength of light in air is Va and λa and that in water is Vw and λw, then the refractive index of water is,

(a) $\frac{{\mathit{V}}_{\mathit{w}}}{{\mathit{V}}_{\mathit{a}}}$

(b) $\frac{{\mathbf{V}}_{\mathbf{a}}}{{\mathbf{V}}_{\mathbf{w}}}$

(c) $\frac{{\mathbf{\lambda }}_{\mathbf{w}}}{{\mathbf{\lambda }}_{\mathbf{a}}}$

(d) $\frac{{\mathbf{V}}_{\mathbf{a}{\mathbf{\lambda }}_{\mathbf{a}}}}{{\mathbf{V}}_{\mathbf{w}}{\mathbf{\lambda }}_{\mathbf{w}}}$

Answer Key:

(b) $\frac{{\mathbf{V}}_{\mathbf{a}}}{{\mathbf{V}}_{\mathbf{w}}}$

 

6. Stars twinkle due to,

(a) reflection
(b) total internal reflection
(c) refraction
(d) polarisation

Answer Key:

(c) refraction 

  
7. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index,
(a) less than one
(b) less than that of glass
(c) greater than that of glass
(d) equal to that of glass

Answer Key:

(d) equal to that of glass 

  
8. The radius of curvature of curved surface at a thin planoconvex lens is 10 cm and the refractive index is 1.5. If the plane surface is silvered, then the focal length will be,
(a) 5 cm 

(b) 10 cm
(c) 15 cm 

(d) 20 cm

Answer Key:

(b) 10 cm

  

9. An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is,

(a) 8 cm 

(b) 10 cm
(c) 12 cm 

(d) 16 cm

Answer Key:

(c) 12 cm  

  
10. A ray of light travelling in a transparent medium of refractive index n falls, on a surface separating the medium from air at an angle of incidents of ${\mathbf{45}}^{\mathbf{°}}$. The ray can undergo total internal reflection for the following n,
(a) n = 1.25 

(b) n = 1.33
(c) n = 1.4 

(d) n = 1.5 

Answer Key: 

(d) n = 1.5 

  

II. Short answer questions.

12th Physics

III. Long answer questions. 

12th Physics

IV. Exercises.   

12th Physics