An object placed on a metre scale at 8 cm mark was focussed on a white screen placed at 92 cm mark, using a converging lens placed on the scale at 50 cm mark.
- Find the focal length of the converging lens.
- Find the position of the image formed if the object is shifted towards the lens at a position of 29.0 cm.
- State the nature of the image formed if the object is further shifted towards the lens.
CBSE OUTSIDE DELHI - SET 1 2013
Download our app for free and get started
Object placed at 8 cm mark,Real image formed at 92 cm mark,
Converging lens is placed at 50 cm mark
This implies that:
Object distance, u = - 42 cm
Image distance, v = + 42 cm
- Focal length, f =?
$\frac{1}{v}-\frac{1}{u} = \frac{1}{f}$
$\Rightarrow \frac{1}{42}- \frac{1}{-42} = \frac{1}{f}$
$\Rightarrow \frac{1}{f} = \frac{1}{42} + \frac{1}{42} = \frac{2}{42} = \frac{1}{21}$
$\therefore f = + \text{ 21 cm}$
Object position is at 29 cm
$\Rightarrow u = - \text{21 cm}$
$v = ?$
$\frac{1}{v} = \frac{1}{f} + \frac{1}{u}$
$\Rightarrow \frac{1}{v} = \frac{1}{21} + \frac{1}{-21}$
$\Rightarrow\frac{1}{v} = \frac{1 - 1}{21}$
$\Rightarrow \frac{1}{v} = \frac{0}{21}$
$\therefore v = \frac{21}{0}$
$\Rightarrow v = \frac{21}{0} = \infty$
So image is formed at infinity.
- If the object is further shifted towards the lens then a virtual, erect and magnified image will be formed behind the object.
Download our appand get started for free
Experience the future of education. Simply download our apps or reach out to us for more information. Let's shape the future of learning together!No signup needed.*
Similar Questions
- 1View SolutionWhich mirror is used as a torch reflector? Draw a labelled diagram to show how a torch reflector can be used to produce a parallel beam of light. Where is the bulb placed in relation to the torch reflector?
- 2View SolutionWhat is the advantage of using a convex mirror as a rear-view mirror in vehicles as compared to a plane mirror? Illustrate your answer with the help of labelled diagrams.
- 3View SolutionThe optical prescription for a pair of spectacles is:
Right eye: 3.50D, Left eye: 4.00D- Are these lenses thinner at the middle or at the edges?
- Which lens has a greater focal length?
- Which is the weaker eye?
- 4View SolutionThe radius of curvature of a concave mirror is 50cm. Where should an object be placed in the mirror, so as to form its image at infinity? Justify your answer.
- 5View SolutionAn object of size 7.0cm is placed at 27cm in front of a concave mirror of focal length 18cm. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained? Find the size and nature of image.
[Hint. Find the value of image distance (v) first. The screen should be placed from the mirror at a distance equal to image distance.] - 6View SolutionDraw labelled ray diagrams to show the formation of images in cases (i) and (ii)above (The diagrams may not be according to scale).
- 7View SolutionAn object of size 7.0cm is placed at a distance of 27cm in front of concave mirror of focal length 18cm. At what distance from the mirror should a screen be placed so that a sharply focused image can be obtained? Find the size and the nature of the image.
- 8View SolutionA concave mirror produces a real image 1cm tall of an object 2.5mm tall placed 5cm from the mirror. Find the position of the image and the focal length of the mirror.
- 9View SolutionHow far should an object be placed from a convex lens of focal length 20 cm to obtain its image at a distance of 30 cm from the lens? What will be the height of the image if the object is 6 cm tall?
- 10View Solution‘‘A lens can form a magnified erect image as well as magnified inverted image of an object placed in front of it.’’ State the nature of this lens and draw ray diagrams to justify the above statement. Mark the positions of O, F and 2F in the diagram.