PoojaMoolya: Created page with "{|border=1 |- || '''Time ''' || '''Narration''' |- || 00:01 || Welcome to the Spoken Tutorial on '''Convex Lenses.''' |- || 00:05 || At the end of this tutorial you will be..."

2020-09-15T05:00:09Z

Created page with "{|border=1 |- || '''Time ''' || '''Narration''' |- || 00:01 || Welcome to the Spoken Tutorial on '''Convex Lenses.''' |- || 00:05 || At the end of this tutorial you will be..."

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{|border=1
|-
|| '''Time '''
|| '''Narration'''

|-
|| 00:01
|| Welcome to the Spoken Tutorial on '''Convex Lenses.'''

|-
|| 00:05
|| At the end of this tutorial you will be able to,

Change the focal length and see the kind of image formed.

|-
|| 00:15
|| Change the object distance and object height and see the kind of image formed.

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|| 00:22
|| Calculate the magnification and length of the telescope tube.

|-
|| 00:27
|| Here I am using,

Ubuntu Linux OS version 16.04, Firefox Web Browser version 62.0.3

|-
|| 00:39
|| To follow this tutorial, learner should be familiar with '''Apps on Physics'''.

|-
|| 00:45
||For prerequisite tutorials please visit this site.

|-
|| 00:50
|| I have already downloaded '''Apps on Physics '''to my '''Downloads''' folder.

|-
|| 00:56
|| In this tutorial we will use,

'''Image Formation by Converging Lenses '''and '''Refracting Astronomical Telescope Apps'''.

|-
|| 01:07
|| Right-click on '''imageconverginglens_en.htm '''file.

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|| 01:14
||Select '''Open With Firefox Web Browser '''option.

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|| 01:19
||'''Image Formation by Converging Lenses App''' opens in the '''browser'''.

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|| 01:25
|| The '''App''' shows a ray diagram of the convex lens.

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|| 01:30
|| Before moving to the '''App''' let us first be familiar with a ray diagram.

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|| 01:37
||Let us define principal axis.

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|| 01:40
||It is an imaginary line passing through the optical center.

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|| 01:46
||A vertical axis divides the lens into two equal halves.

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|| 01:51
||There are four positions on the principal axis.

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|| 01:55
||These positions are 2F, F , F prime and 2 F prime

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|| 02:03
||F is the focal length and 2F is twice the distance of focal length.

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|| 02:10
||F prime and 2F prime are on the opposite side of the lens with the same distance as F and 2F.

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||02:19
|| Now let us open the '''App'''.

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|| 02:22
|| Let us use the scale to spot the positions of focal length F and 2F.

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|| 02:28
|| Initially the object is placed at the zero position of the scale.

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|| 02:34
||The distance of the object from the lens is 50 cm.

|-
|| 02:40
||The vertical black line beyond the lens is a screen.

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|| 02:45
||This screen can be moved back and forth.

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|| 02:50
|| Blue arrow indicates the height of the object.

It is placed beyond 2F.

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|| 02:58
|| 2F is twice the distance of the focal length F.

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|| 03:03
|| From the '''App''', the focal length is 10 cm, so position of 2F has to be at 20 cm.

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|| 03:13
|| Green arrow indicates the image formed by the convex lens.

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||03:18
|| In the green control panel we can edit the values of the following parameters.

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|| 03:24
|| Change the value of '''Focal length''' to 20 cm and press''' Enter'''.

|-
|| 03:31
|| At the bottom of the green panel, there are two radio buttons.

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|| 03:36
||'''Principal light rays''' and '''Bundle of light rays'''.

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|| 03:41
|| By default '''Principal light rays '''option is selected.

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|| 03:47
|| A drop-down is provided to '''Emphasize''' different parameters.

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|| 03:52
|| From the drop-down list, select '''Object distance.'''

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|| 03:57
|| Observe that the '''App '''emphasizes the object distance using a blinking line.

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|| 04:04
||The blinking line disappears after sometime.

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|| 04:09
|| We can also change the object distance by dragging the object.

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|| 04:15
||As we drag, the value in the text-box changes accordingly.

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|| 04:22
|| Press '''F5 '''key on the keyboard to refresh the '''App'''.
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||04:27
|| Now change the value of '''Object height''' to 15 cm.

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|| 04:33
||Change the '''Focal length''' to 20 cm.

|-
|| 04:37
|| Let us learn about the ray diagram.

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|| 04:41
|| The ray emerging from the object is parallel to the principal axis of the lens.

|-
|| 04:48
||This ray after refraction passes through the second principal focus F’.

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|| 04:55
|| A second ray of light passes through the optical center of the lens.

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|| 05:02
||This ray after refraction emerges without any deviation.

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|| 05:08
|| A third ray passes through the first principal focus.

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|| 05:13
||This ray, after refraction, is parallel to the principal axis.

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||05:19
|| The image is formed at point of intersection of the three rays.

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|| 05:25
|| Let us change the position of the object and see where the image appears.

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||05:31
|| Change the '''Object distance '''to 40 cm and '''Object height''' to 10 cm.

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||05:39
|| The '''Kind of image ''' is '''real, inverted '''and '''equal dimension'''.

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|| 05:45
|| This is the condition for''' 2F'''.

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|| 05:49
||When object is at''' 2F''' the image will appear at '''2F'''’.

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|| 05:55
||Here the object distance and height will be equal to image distance and image height.

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||06:03
|| Drag the object between the '''2F''' and '''F.'''

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|| 06:08
||Drag the object to''' 10 cm.'''

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|| 06:12
||Here we can use the scale to take the measurement.

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|| 06:16
|| Observe that the image is formed beyond '''2F’'''.

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|| 06:22
||The image formed is '''real, inverted''' and '''magnified'''.

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|| 06:28
|| Drag the object between '''F''' and optic center.

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|| 06:34
||Drag the object to 30 cm.

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|| 06:38
|| Observe that image is formed at the first principal focus behind the object.

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|| 06:45
||Here the image formed is '''virtual, upright''', and '''magnified'''.

|-
|| 06:52
|| As an assignment

Change the focal length of a convex lens to 10 cm and its object distance to 15 cm.

|-
|| 07:04
||What characteristics of the image do you observe?

|-
|| 07:09
|| Let us move to next '''App'''.

|-
|| 07:13
|| To open the''' App''' right-click on '''refractor_en.htm''' file.

|-
|| 07:21
||Select the option '''Open with Firefox Web Browser'''.

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|| 07:26
|| The '''App '''opens with '''Refracting Astronomical Telescope.'''

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||07:31
|| Before moving to the simulation, please read the information given on the screen.

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||07:38
||Scroll down the screen.

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|| 07:41
|| In the yellow panel, the bigger lens is the objective.

|-
|| 07:46
||The objective has a large focal length.

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||07:50
|| Here the smaller lens is an '''Eyepiece'''.

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|| 07:54
|| The red coloured rays indicate the light from a distant object.

|-
|| 08:00
|| Light rays from a distant object enter the objective lens.

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|| 08:06
||After refraction a real image is formed at the second focal point.

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||08:12
|| Then the eyepiece magnifies the image. The image formed is enlarged and inverted.

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|| 08:21
|| The magnified image of six brightest star of the pleiades is seen in the black circle.

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|| 08:29
|| In the green panel, '''Focal lengths''' of '''Objective''' and '''Eyepiece''' can be edited.

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|| 08:36
|| Here we can vary the '''Focal lengths''' of '''Objective''' and '''Eyepiece''' from 0.05 m to 0.5 m.

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||08:46
|| As per the changes in the '''Focal lengths, App '''calculates '''Angles''' and '''Magnification'''.

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||08:53
|| At the bottom of the screen, '''App''' has given the formula for magnification.

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||08:59
|| That is: '''v'''<nowiki>= - f</nowiki>1/ f2 

|-
|| 09:05
||Here v is the '''Magnification'''

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|| 09:08
||f1 is the focal length of '''Objective''' and f2 is the focal length of '''Eyepiece'''.

|-
|| 09:16
|| Let us calculate the magnification using the formula.

|-
|| 09:21
|| Change the '''Focal length''' of '''Objective''' to 0.45 m and '''Eyepiece''' to 0.1 m.

|-
||09:29
|| Observe that '''App '''has calculated the value for '''Magnification'''.

|-
|| 09:34
|| Notice the changes in the black circle.

|-
|| 09:37
||If we increase the focal length of the '''Objective''', image will be more magnified.

|-
||09:44
|| Let us now calculate the length of the telescope tube.

|-
|| 09:49
|| Change the '''Focal lengths '''of the '''Objective '''and '''Eyepiece''' to their default values.

|-
|| 09:56
||Press '''F5''' key on the keyboard to restart the '''App'''.

|-
||10:01
|| Formula to calculate the length of the telescope tube is sum of the '''Focal lengths''' of '''Objective''' and '''Eyepiece'''.

|-
|| 10:12
||That is: L= f1 + f2.

|-
|| 10:16
||Here f1 is focal length of '''Objective''' and f2 is focal length of '''Eyepiece'''.

|-
|| 10:23
||Substitute the '''Focal lengths''' and calculate the length of the telescope tube.

|-
|| 10:29
||Observe that the length of the telescope is 0.6 m.

|-
|| 10:35
|| Now reverse the '''Focal lengths '''of the '''Objective''' and '''Eyepiece'''.

|-
|| 10:40
|| Observe that the six brightest stars of pleiades appears to be a single point.

|-
|| 10:47
|| This is because the focal length of the '''Objective''' is smaller than that of the '''Eyepiece'''.

|-
|| 10:54
|| As an assignment solve this numerical.

|-
|| 10:59
|| Let us summarise.

|-
|| 11:01
|| Using these '''Apps''' we have,

Changed the focal length and seen the kind of image formed.

|-
|| 11:09
||Changed the object distance and object height and seen the kind of image formed.

|-
|| 11:16
||Calculated the magnification and length of the telescope tube.

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||11:21
|| These Apps are created by Walter-fendt and his team.

|-
|| 11:26
|| The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

|-
|| 11:34
|| The '''Spoken Tutorial Project '''team conducts workshops and gives certificates.

For more details, please write to us.

|-
|| 11:44
|| Please post your timed queries in this forum.

|-
||11:48
||The Spoken Tutorial Project is funded by MHRD, Government of India.

|-
|| 11:54
|| This is Himanshi Karwanje from IIT-Bombay.

Thank you for joining.
|-
|}

Apps-On-Physics/C3/Convex-Lenses/English-timed - Revision history

PoojaMoolya: Created page with "{|border=1 |- || '''Time ''' || '''Narration''' |- || 00:01 || Welcome to the Spoken Tutorial on '''Convex Lenses.''' |- || 00:05 || At the end of this tutorial you will be..."