Airteagal faoi fhoirmiú íomhá trí lionsa scaipthe (lionsa cóncach)
Chun tuiscint a fháil ar fhoirmiú íomhá ag an lionsa cuasach, féach ar na fadhbanna agus na réitigh shamplacha seo a leanas. Sa chás seo, glactar leis go bhfuil an réad ag achar áirithe ón lionsa cuasach,
ansin tarraing foirmiú na híomhá leis an lionsa cóncaibheach, achar na híomhá ón lionsa cóncaibheach agus formhéadú na híomhá leis an lionsa cóncaibheach.
Is é 20 cm fad fócasach lionsa cuasach (lionsa scaipthe). Tá rudaí a bhfuil airde 10 cm orthu suite ar thaobh na láimhe clé den lionsa. Faigh amach an fad ón íomhá, formhéadú na híomhá agus airde na híomhá, más rud é:
a) the object distance is smaller than the focal length of the concave lens
b) the object distance is the same as the focal length of the concave lens
c) the object distance is greater than the focal length of the concave lens
Aitheanta:
The focal length of the concave lens (f) = -20 cm
The focal length of the concave lens has a negative sign because the focal point of the concave lens is virtual, where the light beam does not pass through the focal point.
The height of object (h) = 10 cm
réiteach:
Tá an fad ón réada níos lú ná fad fócasach an lionsa chóncaigh (do > f)
Abair go bhfuil an fad idir an réada 5 cm, 10 cm agus 15 cm.
a) The focal length is -20 cm and if the object distance (do) = 5 cm
An fad íomhá (di)
1/di = 1/f – 1/do = -1/20 – 1/5 = -1/20 – 4/20 = -5/20
trastomhas = -20/5 = -4 cm
The image distance sign, negative, means the image is virtual, where the beam of light does not pass through the image.
The image distance, 4 cm, smaller than the object distance, 5 cm.
Formhéadú na híomhá (M)
M = -di / déan = -(-4)/5 = 4/5 = 0.8
The magnification of image smaller than 1 means that the image is reduced, or the image size is smaller than the object size.
The height of image (h’)
The equation of the magnification of image :
M = u' / u
h' = M h = (0.8)(10 cm) = 8 cm
The height of image is sign positive, means that the image is upright.
b) The focal length is -20 cm and if the object distance (do) = 10 cm
An fad íomhá (di)
1/di = 1/f – 1/do = -1/20 – 1/10 = -1/20 – 2/20 = -3/20
trastomhas = -20/3 = -6.7 cm
The image distance is negative, means that the image is virtual, where the beam of light does not pass through the image.
The image distance 6.7 cm, smaller than the object distance, 10 cm.
Formhéadú na híomhá (M)
M = -di / do = -(-6.7)/10 = 6.7 / 10 = 0.67
The magnification of image is smaller than 1 means that the image is reduced, or the image size is smaller than the object size.
The height of image (h’)
Cothromóid formhéadúcháin íomhá:
M = u'/u
h' = M h = (0.67)(10 cm) = 6.7 cm
The height of image is sign positive, means that the image is upright.
c) The focal length is -20 cm and the object distance (do) = 15 cm
An fad íomhá (di)
1/di = 1/f – 1/do = -1/20 – 1/15 = -3/60 – 4/60 = -7/60
trastomhas = -60/7 = -8.6 cm
The image distance is negative, means that the image is virtual, where the beam of light does not pass through the image.
The image distance is 8.7 cm, smaller than the object distance, 15 cm.
Formhéadú na híomhá (M)
M = -di / do = -(-8.6)/10 = 8.6 / 10 = 0.86
The magnification of image smaller than 1 means that the image size is smaller than the object size.
The height of image (h’)
Cothromóid formhéadúcháin íomhá:
M = u'/u
h' = M h = (0.86)(10 cm) = 8.6 cm
The height of the image is positive, means that the image is upright.
The object distance is the same as the focal length of the concave lens (do = f)
An fad fócasach (f) = an fad ón réada (do) = 20 cm.
An fad íomhá (di)
1/di = 1/f – 1/do = -1/20 – 1/20 = -2/20 = -2/20
trastomhas = -20/2 = -10 cm
The image distance is negative, means that the image is virtual, where the beam of light does not pass through the image.
The image distance is 10 cm, smaller than the object distance, 20 cm.
Formhéadú na híomhá (M)
M = -di / déan = -(-10)/20 = 10/20 = 0.5
The magnification of image is smaller than 1, means that the image size is smaller than the object size.
The height of the image (h’)
The equation of the magnification of the image :
M = u'/u
h' = M h = (0.5)(10 cm) = 5 cm
The height of the image is positive, means that the image is upright.
Tá an fad ón réada níos mó ná fad fócasach an lionsa chóncaigh (do > f)
Suppose the distance of objects is 30 cm and 40.
a) The focal length is -20 cm and if the object distance (do) = 30 cm
An fad íomhá (di)
1/di = 1/f – 1/do = -1/20 – 1/30 = -3/60 – 2/60 = -5/60
trastomhas = -60/5 = -12 cm
The image distance is negative, means that the image is virtual, where the beam of light does not pass through the image.
The image distance is 12 cm, smaller than the object distance of 30 cm.
Formhéadú na híomhá (M)
M = -di / déan = -(-12)/30 = 12/30 = 0.4
The magnification of image smaller than 1, means that the image size is smaller than the object size.
The height of image (h’)
Cothromóid formhéadúcháin íomhá:
M = u'/u
h' = M h = (0.4)(10 cm) = 4 cm
The height of image is sign positive, means that the image is upright.
b) The focal length -20 cm and if the object distance (do) = 40 cm
An fad íomhá (di)
1/di = 1/f – 1/do = -1/20 – 1/40 = -2/40 – 1/40 = -3/40
trastomhas = -40/3 = -13 cm
The image distance is negative, means that the image is virtual, where the beam of light does not pass through the image.
The image distance is 13 cm, smaller than the object distance 40 cm.
Formhéadú na híomhá (M)
M = -di / déan = -(-13)/40 = 13/40 = 0.3
The magnification of image smaller than 1, means that the image size is smaller than the object size.
The height of the image (h’)
The equation of the magnification of the image:
M = u'/u
h' = M h = (0.3)(10 cm) = 3 cm
The height of the image is signed positive, means that the image is upright.
