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Question
Study the diagram given below.
- Name the lens LL’.
- What are the points O and O’ called?
- Complete the diagram to form the image of the object AB.
- State the three characteristics of the image.
- Name a device in which this action of lens is used.
Solution
- LL' lens is a convex lens.
- O and O' are known as first and second focal points respectively.
- Three characteristics of image are
- Image is virtual
- Erect
- Magnified
- Such action of lens is used in a magnifying glass or a simple microscope.
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RELATED QUESTIONS
An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.
Which of the object distances gives the biggest image?
The diagram alongside shows the refraction of a ray of light from sir to a liquid.
(a) write the values of (i) angle of incidence, (ii) angle of refraction.
(b) use snell’s law to find the refractive index of liquid with respect to air.
Define the term principal axis of a lens.
The given below figure shows an object OA and its image IB formed by a lens
. 
draw suitable rays to locate the lens and its focus.
State two applications of a convex lens.
For finding the focal length of a convex lens by obtaining the image of a distant object, one should use as the object.
(1) a well lit distant tree
(2) window grill in the class room
(3) any distant tree
(4) a lighted candle kept at the other end of the table.
i. Which type of microscope has the arrangement of lenses shown in the adjoining figure?
ii. Label the figure correctly.
iii. Write the working of this microscope.
iv. Where does this microscope used?
v. Suggest a way to increase the efficiency of this microscope.
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The above images are that of a specialized slide projector. Slides are small transparencies mounted in sturdy frames ideally suited to magnification and projection since they have a very high resolution and a high image quality. There is a tray where the slides are to be put into a particular orientation so that the viewers can see the enlarged erect images of the transparent slides. This means that the slides will have to be inserted upside down in the projector tray.
To show her students the images of insects that she investigated in the lab, Mrs. Iyer brought a slide projector. Her slide projector produced 500 times enlarged and inverted image of a slide on a screen 10 m away.
a. Based on the text and data given in the above paragraph, what kind of lens must the slide projector have?
b. If v is the symbol used for image distance and u for object distance then with one reason state what will be the sign for `"𝑣"/"𝑢"` in the given case?
c. A slide projector has a convex lens with a focal length of 20 cm. The slide is placed upside down 21 cm from the lens. How far away should the screen be placed from the slide projector’s lens so that the slide is in focus?
OR
c. When a slide is placed 15 cm behind the lens in the projector, an image is formed 3 m in front of the lens. If the focal length of the lens is 14 cm, draw a ray diagram to show image formation. (not to scale)
