RAY-OPTICS-AND-OPTICAL-INSTRUMENTS-QUIZ13

 

Ray Optics and Optical Instruments Quiz-13

Dear Readers,

As per analysis for previous years, it has been observed that students preparing for NEET find Physics out of all the sections to be complex to handle and the majority of them are not able to comprehend the reason behind it. This problem arises especially because these aspirants appearing for the examination are more inclined to have a keen interest in Biology due to their medical background. Furthermore, sections such as Physics are dominantly based on theories, laws, numerical in comparison to a section of Biology which is more of fact-based, life sciences, and includes substantial explanations. By using the table given below, you easily and directly access to the topics and respective links of MCQs. Moreover, to make learning smooth and efficient, all the questions come with their supportive solutions to make utilization of time even more productive. Students will be covered for all their studies as the topics are available from basics to even the most advanced. .

Q1.  A monochromatic beam of light passes from a denser medium into a rarer medium. As a result

•  Its velocity increases
•  Its velocity decreases
•  Its frequency decreases
•  Its wavelength decreases

Solution
𝑣 ∝ 1/𝜇 ,𝜇rarer < 𝜇denser

Q2. In an astronomical telescope in normal adjustment, a straight black line of length 𝐿 is drawn on the objective lens. The eyepiece forms a real image of this line. The length of this image is 𝑙. The magnification of the telescope is

•   𝐿/𝑙
•   𝐿/𝑙 + 1
•   𝐿/𝑙− 1
•   𝐿 + 𝑙/𝐿 − 𝑙

Solution
Here we treat the line on the objective as the object and the eyepiece as the lens

Hence 𝑢 = −(𝑓_o+ 𝑓_e) and 𝑓 = 𝑓_e 

Now 1/𝑣 − 1 /−(𝑓_o+𝑓_e) = 1/𝑓_e 

Solving we get 𝑣 = (𝑓_o+𝑓_e)𝑓_e /𝑓_o 

Magnification = |𝑣/𝑢| = 𝑓_e/𝑓_o = Image size/Object size = 𝑙/𝐿 

∴ Magnification of telescope in normal adjustment = 𝑓₀/𝑓 _e = 𝐿/𝑙

Q3.   A microscope is focused on an ink mark on the top of a table. If we place a glass slab of 3 cm thick on it, how should the microscope be moved to focus the ink spot again? The refractive index of glass is 1.5.

•   2 cm upwards
•   2 cm downwards
•   1 cm upwards
•   1 cm downwards

Solution
Given, 𝑛 = 1.5, ℎ₀ = 3

 𝑛 = ℎ₀ℎ₁ 

 1.5 = 3/ℎ₁ 

 ℎ_i= 3/1.5 = 2 𝑐𝑚

 Hence, 3-2 = 1 cm upwards

Q4.  With respect to air critical angle in a medium for light of red colour (𝜆1) is 𝜃. Other facts remaining same, critical angle for light of yellow colour [𝜆2] will be

•   𝜃
•   More than 𝜃
•  Less than 𝜃
•   𝜃𝜆₁/𝜆₂

Solution
Critical angle = sin^-1 (1/𝜇) 

∴ 𝜃 = sin^-1 ( 1/𝜇_𝜆1) and 𝜃′ = sin^-1 ( 1 𝜇 _𝜆2)

 Since 𝜇_𝜆2 > 𝜇 _𝜆1, hence 𝜃′ < 𝜃

Q5. Total internal reflection of a ray of light is possible when the (𝑖_c = critical angle, 𝑖 = angle of incidence)

•   Ray goes from denser medium to rarer medium and 𝑖 < 𝑖_c
•   Ray goes from denser medium to rarer medium and 𝑖 > 𝑖_c
•   Ray goes from rarer medium to denser medium and 𝑖 > 𝑖_c
•   Ray goes from rarer medium to denser medium and 𝑖 < 𝑖_c

Solution
  Ray goes from denser medium to rarer medium and 𝑖 > 𝑖_c .

Q6. What is the time taken (in 𝑠𝑒𝑐𝑜𝑛𝑑𝑠) to cross a glass of thickness 4 𝑚𝑚 and 𝜇 = 3 by light

•   4 × 10^-11
•   2 × 10^-11
• 16 × 10^-11
•   8 ×10^-10

Solution
𝑡 = 𝜇𝑥/𝑐 = (3 × 4 × 10^-3)/(3 × 10⁸ ) = 4 × 10^-11𝑠

Q7. . A compound microscope has an objective and eye-piece as thin lenses of focal lengths 1 cm and 5 cm respectively. The distance between the objective and the eye-piece is 20 cm. The distance at which the object must be placed infront of the objective if the final image is located at 25 cm from the eye-piece, it numerically

•   95/6 cm
•   5 cm
•   95/89 cm
•   25/6 cm

Solution

For the eye-piece 𝑣_e= −25 cm,𝑓_e= 5 cm

 1/−25 − 1/𝑢_e= 1/5 

Or 1/𝑢_e = − 1/25 − 1/5

or 1/𝑢_e = − −1−5/25 

 Or 𝑢_e = − 25/6 

Now , 𝑣_o = 𝐿 − |𝑢_e| = 20 − 25/6= (120 − 25)/6cm =95/6cm 

 Now, 1 /(95/6)−1/𝑢_o= 1/1 or 1/𝑢_O=6/95− 1

 Or 𝑢₀ = −95/89cm or |𝑢_o| = 95/89cm

Q8. From which source a continuous emission spectrum and a line absorption spectrum are simultaneously obtained

•  Bunsen burner flame
• The sun
•  Tube light
•   Hot filament of an electric bulb

Solution
The sun

Q9. In a thin prism of glass (refractive index 1.5), which of the following relations between the angle of minimum deviations 𝛿𝑚 and angle of refraction 𝑟 will be correct

•   𝛿_m= 𝑟
•  𝛿_m = 1.5𝑟
•   𝛿_m= 2𝑟
•   𝛿_m = 𝑟/2

Solution
𝛿𝑚 = (𝜇 − 1)(2𝑟) = (1.5 − 1)2𝑟 = 0.5 × 2𝑟 = 𝑟

Q10.  A person cannot see properly beyond 2 m. Power of the lens is

•   0.5 D
•   1.5 D
•   -2.5 D
• -0.5 D

Solution
Focal length of eye lens = −2 𝑚 So , power of lens = 1/𝑓 = 1/−2 = -0.5 D (short-sighted)