1. A 2 mm high object is placed 10 cm from a glainne-mheudachaidh. Near point N = 25 cm. Determine the angular magnification and image height.
Aithnichte:
Object height (ho) = 2 mm
Puing faisg air làimh (N) = 25 cm
Rud astar (do) = 10 cm
A dhìth: Angular magnification (M) and image height (hi)
fuasgladh:
M = N / s
M = 25 cm / 10 cm
M = 2.5
The image height = 2.5 x 2 mm = 5 mm.
2. A 25 cm focal length lens is used as magnifying glass. Determine (a) angular magnification when the shùil is focused at its near point N = 25 cm (b) angular magnification when the eye is relaxed.
Aithnichte:
Puing faisg air làimh (N) = 25 cm
The focal length of a magnifying glass (f) = 25 cm
The plus sign indicates that the lens is a converging lens.
fuasgladh:
(a) angular magnification when the eye is focused at its near point N = 25 cm
M = (N/f) + 1
M = (25 cm / 25 cm) + 1
M = 1 + 1
M = 2 X
If the object height is 1 cm, the image height is 2 x 1 cm = 2 cm.
(b) angular magnification when the eye is relaxed
M = N / f
M = (25 cm / 25 cm)
M = 1 X
If the object height is 1 cm, the image height is 1 x 1 cm = 1 cm.
3. A 1 cm high object is placed in front of a 10 cm focal length lens. Determine (a) the image height when the shùil is focused at its near point N = 25 cm (b) The image height when the eye is relaxed.
Aithnichte:
The object height (ho) = 1 cm
The focal length (f) = 10 cm
Puing faisg air làimh (N) = 25 cm
fuasgladh:
(a) The image height when the eye is focused at its near point N = 25 cm
M = (N/f) + 1
M = (25 cm / 10 cm) + 1
M = 2.5 + 1
M = 3.5 X
If the object height is 1 cm, the image height is 3.5 x 1 cm = 3.5 cm.
(b) The image height when the eye is relaxed.
M = N/f
M = 25 cm / 10 cm
M = 2.5 X
If the object height is 1 cm, the image height is 2.5 x 1 cm = 2.5 cm.
4. The angular magnification when the eye is relaxed = 5X. If near point = 25 cm, what is the focal length of the magnifying glass ?
Aithnichte:
Object height (ho) = 2 mm
Angular magnification (M) = 5X
Puing faisg air làimh (N) = 25 cm
Ag iarraidh: Am fad fòcasach
fuasgladh:
The formula of the angular magnification when the eye is relaxed :
M = N/f
5 = 25 cm / f
f = 25 cm / 5
f = 5 cm
The focal length of the magnifying glass = 5 cm.
5. An object is seen by someone with a magnifying glass with the focal length is 15 cm. If the near point of the person’s eyes = 30 cm, then determine the overall magnification of the magnifying glass.
Aithnichte:
The near point of the normal eye (N) = 30 cm
The focal length of the magnifying glass (f) = 15 cm (plus sign because the glass is convergent)
A dhìth: the maximum magnification
fuasgladh:
The maximum magnification occurs when the accommodation of eye is maximum. The angular magnification of the magnifying glass occurs when the accommodation of eye is maximum :
M = (N/f) + 1
M = (30 cm / 15 cm) + 1
M = 2 + 1
M = 3 amannan
6. A magnifying glass with the optical power 20 diopters used by a person with the normal eyes 25 cm. If the accommodation is minimum, determine the minimum magnification.
Aithnichte:
Near point of the normal eye (N) = 25 cm
Power of the magnifying glass (P) = 20 diopters
Ag iarraidh: The minimum magnification
fuasgladh:
The focal length of the magnifying glass :
P = 1/f
20 = 1/f
f = 1/20
f = 0.05 meters
f = 5 cm
The angular magnification when the accommodation is minimum :
M = N / f
M = (25 cm / 5 cm)
M = 5 times
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