REFRACTION THROUGH A LENS

Detailed Study:

• Lens and its Components

• Refraction through a lens and its Focus

• Action of Lens as a set of Prisms

• Ray Diagrams - Principal Rays

• Ray Diagrams - Convex Lens

• Ray Diagrams - Concave Lens

• Sign Conventions & Lens Formula

• Problems on Lenses

• Problems on Magnification of Lenses

• Power and Applications of Lenses

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Frequently Tested Topics:​

• Ray diagrams for convex and concave lens at different positions

• Applications of lenses

• Problems based on lens formula and magnification

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Important Past Questions:

• If a lens is placed in water instead of air, how does the focal length change? (2019)

• Which lens, thick or thin, has a greater focal length? (2019)

• The power of a lens is -5D.

        i) Find its focal length.

        ii) Name the type of lens.   

        (2018)

• State the position of the object in front of a converging lens if:

       i) it produces a real and same size image of the object

       ii) it is used as a magnifying lens             (2018)

• You are provided with a printed piece of paper. Using this paper how will you differentiate between a convex lens and a concave lens? (2012)

• When does a ray of light falling on a lens pass through it undeviated? (2011)

• Which lens can produce a real and inverted image of an object? (2011)

• We can burn a piece of paper by focusing the sun rays by using a particular type of lens.

       i) Name the type of lens used for this purpose.

       ii) Draw a ray diagram to support your answer.     

       (2010)

• Copy and complete the following table:   (2009)

Type of lens            Position of object             Nature of image               Size of image

Convex                   At F

Concave                 At infinity

• An object is placed in front of a converging lens at a distance greater that twice the focal length of the lens. Draw a ray diagram to show the formation of the image. (2007)

• An object is placed in front of a convex lens such that the image formed has the same size as that of the object. Draw a ray diagram to illustrate this. (2006)

• A virtual, diminished image is formed when an object is placed between the optical center and the principal focus of a lens.

i) Name the type of lens which forms the above image. 

ii) Draw a ray diagram to show the formation of the image with the above stated characteristics.       

(2019)

• A lens forms an upright and diminished image of an object when the object is placed at the focal point of the given lens.

i) Name the lens.

ii) Draw a ray diagram to show the image formation.           

(2017)

• A lens produces a virtual image between the object and lens.

i) Name the lens.

ii) Draw a ray diagram to show the formation of this image. 

 (2016)

• Where should an object be placed so that a real and inverted image of the same size as the object is obtained using a convex lens? Draw a ray diagram to show the formation of the image as specified above.        (2015)

• A lens forms an erect, magnified and virtual image of an object.

i) Name the lens.

ii) Draw a labelled ray diagram to show the image formation.

iii) The lens mentioned above is of focal length 25cm. Calculate the power of the lens.       

(2014)

• Define power of a lens. (2014)

• A linear object is placed on the axis of a lens. An image is formed by refraction in the lens. For all positions of the object on the axis of the lens, the positions of the image are always between the lens and the object.

i) Name the lens.

ii) Draw a ray diagram to show the formation of the image of an object placed in front of the lens at any position of your choice except infinity.

(2008)

• An object is placed at a distance 24cm in front of a convex lens of focal length 8cm.

i) What is the nature of the image so formed?

ii) Calculate the distance of the image from the lens.

iii) Calculate the magnification of the image.

(2019)

• An object is placed at a distance of 12cm from a convex lens of focal length 8cm. Find:

i) the position of the image

ii) nature of the image

(2018)

• Ranbir claims to have obtained an image twice the size of the object with a concave lens. Is he correct? Give a reason. (2014)

• A converging lens is used to obtain an image of an object placed in front of it. The inverted image is formed between F2 and 2F2 of the lens. 

i) Where is the object placed?

ii) Draw a ray diagram to illustrate the formation of the image obtained.

(2012)

• An object is placed in front of a lens between its optical center and the focus and forms a virtual, erect and diminished image.

i) Name the lens which formed this image.

ii) Draw a ray diagram to show the formation of the image with the above stated characteristics. 

(2011)

• An erect, magnified and virtual image is formed when an object is placed between the optical center and principal focus of a lens.

i) Name the lens.

ii) Draw a ray diagram to show the formation of the image with the above stated characteristics. 

(2010)

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