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**PHYSICS InClass by SSL Technologies with S. Lancione Exercise-53**

High School InClass by SSL Technologies with S. Lancione Exercise-53 Lenses Part 2 /2

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Lenses PART-2 /2 THE EYE The eye is an optical “instrument”. It contains a converging lens used to focus images on the “retina” (a kind of screen at the back of the eye). Images on the retina are inverted. Click

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**Lenses PART-2 DEFECTS IN VISION**

NEARSIGHTEDNESS The ability to see objects clearly which are near but objects far away appear blurred. Nearsightedness, known as myopia, is caused by the fact that rays of light focus in front of the retina of the eye. Myopia is corrected by using a diverging lens as illustrated in the diagram below. FARSIGHTEDNESS The ability to see objects clearly which are far but objects close to the eye appear blurred. Farsightedness, known as hyperopia, is caused by the fact that rays of light focus behind the retina of the eye. Hyperopia is corrected by using a converging lens. Click

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Lenses PART-2 CORRECTING DEFECTS IN VISION Click

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Lenses PART-2 Reminder In applying the lens equation, be sure to use the signs carefully : do is the object distance and is always positive f is the focal length and is positive for convex lenses but negative for concave lenses di is the image distance and is positive for real images but negative for virtual images Click

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EXERCISES

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**Remember: A negative di indicates a virtual image.**

Question-1 A lens forms an image 10 cm high. If the object is 4 cm in height and situated 8 cm away, what is the focal length of the lens? Remember: A negative di indicates a virtual image. 8 Note that while the standard unit for length in a physics formula is the meter, since in this case we have lengths on both sides of the equation, we need not convert to meters as the units automatically cancel out. Click

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**Question-2 Virtual 6 cm 0.4 0.8 cm Upright**

The focal length of a concave lens is 10 cm. An object, whose height is 2 cm, is placed 15 cm in front of the lens. Determine the characteristics of the image. Type (real or virtual): _______________ Location: _______________ Magnification: _______________ Height: _______________ Attitude (upright/inverted): _______________ Virtual 6 cm When the magnification is less than one, the image is smaller than the object. 0.4 0.8 cm Upright Negative image distance means a virtual image. Click

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**Question-3 Virtual 24 cm 4 16 cm Upright**

An object whose height is 4 cm is placed 6 cm in front of a converging lens. If the focal length of the lens is 8 cm, determine the characteristics of the image. Type (real or virtual): _______________ Location: _______________ Magnification: _______________ Height: _______________ Attitude (upright/inverted): _______________ Virtual 24 cm When the magnification is greater than one, the image is greater than the object. 4 16 cm Upright Click

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Question-4 The focal length of a camera is 10 cm. The lens forms an image that is 4 cm high when the negative (film) is 12 cm from the lens. a) What is the object distance? Click

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**Question-4 The negative sign indicates inversion.**

The focal length of a camera is 10 cm. The lens forms an image that is 4 cm high when the negative (film) is 12 cm from the lens. do = 60 cm (previously calculated) b) What is the object height? The negative sign indicates inversion. Click

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**Question-4 The negative sign indicates inversion.**

The focal length of a camera is 10 cm. The lens forms an image that is 4 cm high when the negative (film) is 12 cm from the lens. ho = 20 cm (previously calculated) c) What is the magnification factor? The negative sign indicates inversion. Click

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Question-5 A 35 mm slide (the object) is placed 8.2 cm from a projection lens whose focal length is 8 cm. Determine: a) The image distance. Click

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**Question-5 The negative sign indicates inversion.**

A 35-mm slide (the object) is placed 8.2 cm from a projection lens whose focal length is 8 cm. Determine: b) The image height. The negative sign indicates inversion. Click

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**Question-5 The negative sign indicates inversion.**

A 35-mm slide (the object) is placed 8.2 cm from a projection lens whose focal length is 8 cm. Determine: c) The magnification factor. The negative sign indicates inversion. Click

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Question-6 The focal length of a magnifying glass is 10 cm. The lens is used to view a stamp that is 2.0 cm in height. If the stamp is placed 6.0 cm away from the magnifying glass, calculate the height of the image. Click

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**The negative sign indicates a virtual image.**

Question-7 Reminder : concave lenses have a negative focal length. An object is 4 cm from a concave lens whose focal length is 12 cm. Where will the image be located? The negative sign indicates a virtual image. Click

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**The negative sign indicates a virtual image.**

Question-8 An object 3 cm high is located 30 cm from a concave lens whose focal length is 15 cm. Determine: a) The image distance. The negative sign indicates a virtual image. Click

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Question-8 An object 3 cm high is located 30 cm from a concave lens whose focal length is 15 cm. Determine: b) The magnification. Click

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**Question-8 Virtual Upright**

An object 3 cm high is located 30 cm from a concave lens whose focal length is 15 cm. Determine: c) The size of the image. Virtual d) The type of image: ___________________ Upright e) The attitude of the image: ___________________ Click

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**Question-9 The problem of not seeing far objects clearly.**

Define each of the following terms : a) Myopia: The problem of not seeing far objects clearly. b) Hyperopia: The problem of not seeing near objects clearly. Click

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**Question-10 Myopia Hyperopia**

Illustrated below are two common eye problems or defects. State the name of each defect and draw the appropriate lens in order to correct the problem. Myopia Hyperopia Click

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