SATHEE: Optics 1 Question 2

Optics 1 Question 2

2. A concave mirror for face viewing has focal length of $0.4 m$ . The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is

(2019 Main, 9 April I)

(a) $0.16 m$

(b) $1.60 m$

(d) $0.24 m$

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Answer:

Correct Answer: 2. (c)

Solution:

Given, focal length of concave mirror,

$f = - 0.4 m$

Magnification $= 5$

We know that, magnification produced by a mirror,

$\begin{aligned} m = - \frac{image distance}{object distance} \\ \Rightarrow & \frac{v}{u} = - 5 or v = - 5 u \end{aligned}$

Using mirror formula,

$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$

Substituting the given values in the above equation, we get

$\begin{aligned} \Rightarrow & \frac{1}{- 5 u} + \frac{1}{u} & = - \frac{1}{0.4} \\ \Rightarrow & \frac{4}{5 u} & = - \frac{1}{0.4} \\ \Rightarrow & u & = - \frac{1.6}{5} = - 0.32 m \end{aligned}$

Alternate Solution

Magnification produced by a mirror can also be given as

$m = \frac{f}{f - u}$

Substituting the given values, we get

$\begin{aligned} 5 & = \frac{- 0.4}{- 0.4 - u} \\ u & = - 0.32 m \end{aligned}$

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Optics 1 Question 2

2. A concave mirror for face viewing has focal length of $0.4 m$ . The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is

Answer:

Alternate Solution

इंजीनियरिंग की तैयारी

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नमूना मॉक टेस्ट

सदस्यता

एनसीईआरटी व्यायाम वीडियो समाधान

Optics 1 Question 2

2. A concave mirror for face viewing has focal length of 0.4m. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is

Answer:

Alternate Solution

इंजीनियरिंग की तैयारी

चिकित्सा तैयारी

एनसीईआरटी पुस्तकें और समाधान

महत्वपूर्ण संसाधन

अन्य संसाधन

पाठ्यक्रम

परीक्षा मंच

नमूना मॉक टेस्ट

सदस्यता

एनसीईआरटी व्यायाम वीडियो समाधान

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2. A concave mirror for face viewing has focal length of $0.4 m$ . The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is