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рдкреНрд░рд╢реНрди
Yesh find out F1 and F2 of symmetric convex lens experimentally then which conclusion is true.
рд╡рд┐рдХрд▓реНрдк
a) ЁЭР╣1 = ЁЭР╣2
b) ЁЭР╣1 > ЁЭР╣2
c) ЁЭР╣1 < ЁЭР╣2
d) ЁЭР╣1 ≠ ЁЭР╣2
рдЙрддреНрддрд░
a) ЁЭР╣1 = ЁЭР╣2
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(a) Draw a ray diagram to show the formation of an image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
(b) In the above ray diagram, mark the object distance (u) and the image distance (v) with their proper signs (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.
(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.
"A convex lens can form a magnified erect as well as magnified inverted image of an object placed in front of it." Draw ray diagram to justify this statement stating the position of the object with respect to the lens in each case.
A student has obtained a magnified image of a flame on a screen using a convex lens. To draw the corresponding ray diagram to show the image formation, which of the following two rays whose paths after refraction are shown, should he select ?
(A) I and II
(B) II and III
(C) III and IV
(D) I and III
Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :
| S. No. | Object-Distance u (cm) |
Image-Distance v (cm) |
| 1 | –100 | +25 |
| 2 | –60 | +30 |
| 3 | –40 | +40 |
| 4 | –30 | +60 |
| 5 | –25 | +100 |
| 6 | –15 | +120 |
(a) What is the focal length of the convex lens? Give reason to justify your answer.
(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?
(c) Select an appropriate scale and draw a ray diagram for the observation at S.No. 2. Also find the approximate value of magnification.
Draw a ray diagram to show the formation of the image of 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 labelled ray diagram to show how a ray of light passes through a parallel sided glass block:
if it hits the glass block at 90° (that is, perpendicular to the glass block)
Where should an object be placed in order to use a convex lens as a magnifying glass?
Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image?
What type of lens would you use as a magnifying glass? How close must the object be to the lens?
With the help of a labelled diagram explain how a convex lens converges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the convex lens on the diagram.
An object 3 cm high is placed 24 cm away from a convex lens of focal length 8 cm. Find by calculations, the position, height and nature of the image.
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.
Rewrite the image distances in the correct order.
What kind of lens can form:
am erect diminished image?
Which causes more bending (or more refraction) of light rays passing through it : a convex lens of long focal length or a convex lens of short focal length?
A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
(a) +10 cm
(b) +20 cm
(c) −10 cm
(d) −20 cm
What type of lens is used to correct
hypermetropia
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.
Show by a diagram the refraction of two light rays incident parallel to the principal axis on a convex lens by treating it as a combination of a glass slab and two triangular glass prisms.
A parallel oblique beam of light falls on a convex lens. Draw a diagram to show the refraction of light through the lens.
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.
Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations:
| S. No. | Object-Distance u (cm) |
Image-Distance v (cm) |
| 1 | –60 | +12 |
| 2 | –30 | +15 |
| 3 | –20 | +20 |
| 4 | –15 | +30 |
| 5 | –12 | +60 |
| 6 | –9 | +90 |
(a) What is the focal length of the convex lens? State reason for your answer.
(b) For what object-distance (u) is the corresponding image-distance (v) not correct? How did you arrive at this conclusion?
(c) Choose an appropriate scale to draw a ray diagram for the observation at S. No. 4 and find the approximate value of magnification.
To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.
(a) In which direction-towards or away from the lens does he move the screen to focus the object?
(b) How does the size of image change?
(c) Approximately at what distance does he obtain the image of magnification –1?
(d) How does the intensity of image change as the object moves farther and farther away from the lens?
(a) What type of a lens can be used as a magnifying glass?
(b) Show by a ray diagram the formation of a real image by simple magnifying lens.
If an object is placed in front of a convex lens beyond 2F1, then what will be the position, relative size, and nature of an image which is formed? Explain with a ray diagram.
Point out the difference between a convex lens and a concave lens.
What happens to the image formed by a convex lens if its lower part is blackened?
A candle is placed between f and 2f a convex lens. Draw a ray diagram showing the position of the image.
Find the odd one out and give its explanation.
Write scientific reason.
Adults need bifocal lens spectacle.
Observe the given figure and answer the following questions.
- Where is the above type of lens construction used?
- What type of image is formed by an objective lens?
- What happens instead of placing at Fo if the object is placed in between O and Fo?
Which of the following statements is true?
Which of the following statements is true?
A convex lens of focal length 20 cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?
Distinguish between:
Concave lens and Convex lens
