11. Wavelength of light of frequency 100 Hz  
    

1. 1. 2 × 10⁶ m

   
   
   

   2. 3 × 10⁶ m

   
   
   

   3. 4 × 10⁶ m

   
   
   

   4. 5 × 10⁶ m

   
   
   

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1. View Hint View Answer Discuss in Forum

   Frequency (n) = 100 Hz
   ​v = n λ
   

   λ =	3 × 108
   	100

   
   [where, velocity of light (v) = 3 × 10⁸ m/s] ​
   λ = 3 × 10⁶ m

   Correct Option: B

   Frequency (n) = 100 Hz
   ​v = n λ
   

   λ =	3 × 108
   	100

   
   [where, velocity of light (v) = 3 × 10⁸ m/s] ​
   λ = 3 × 10⁶ m

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12. An air bubble in a glass slab (µ = 1.5) is 5 cm deep when viewed from one face and 2 cm deep when viewed from the opposite face. The thickness of the slab is​​
    

1. 1. 7.5 cm

   
   
   

   2. 10.5 cm

   
   
   

   3. 7 cm

   
   
   

   4. 10 cm

   
   
   

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1. View Hint View Answer Discuss in Forum

   1.5 =	Real depth (R1)
   	Apparent depth (5 cm)

   
   R₁ = 1.5 × 5 = 7.5 cm
   
   

   For opposite face , 1.5 =	R2	⇒ R2 = 3 cm
   	2

   
   ∴ Thickness of the slab = R₁ + R₂ ​​​​
   = 7.5 + 3 = 10.5 cm

   Correct Option: B

   1.5 =	Real depth (R1)
   	Apparent depth (5 cm)

   
   R₁ = 1.5 × 5 = 7.5 cm
   
   

   For opposite face , 1.5 =	R2	⇒ R2 = 3 cm
   	2

   
   ∴ Thickness of the slab = R₁ + R₂ ​​​​
   = 7.5 + 3 = 10.5 cm

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13. The reddish appearance of the sun at sunrise and sunset is due to
    

1. 1. the colour of the sky

   
   
   

   2. ​the scattering of light

   
   
   

   3. the polarisation of light

   
   
   

   4. the colour of the sun

   
   
   

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1. View Hint View Answer Discuss in Forum

   It is due to scattering of light.
   

   Scattering ∝	1
   	λ4

   
   Hence the light reaches us is rich in red.
   

   Correct Option: B

   It is due to scattering of light.
   

   Scattering ∝	1
   	λ4

   
   Hence the light reaches us is rich in red.
   

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14. Two plane mirrors are inclined at 70°. A ray incident on one mirror at angle θ after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of θ is
    

1. 1. 50°

   
   
   

   2. 45° ​

   
   
   

   3. 30°

   
   
   

   4. 55°

   
   
   

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1. View Hint View Answer Discuss in Forum

   
   From fig. 40° + θ = 90°
   ∴ θ = 90° – 40° = 50°

   Correct Option: A

   
   From fig. 40° + θ = 90°
   ∴ θ = 90° – 40° = 50°

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15. A person is six feet tall. How tall must a vertical mirror be if he is able to see his entire length? ​
    

1. 1. 3 ft

   
   
   

   2. 4.5 ft

   
   
   

   3. 7.5 ft

   
   
   

   4. 6 ft

   
   
   

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1. View Hint View Answer Discuss in Forum

   To see his full image in a plane mirror a person requires a mirror of at least half of his height.
   
   

   Correct Option: A

   To see his full image in a plane mirror a person requires a mirror of at least half of his height.
   
   

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