an image 2/3 the size the object is formed by a concave mirror at a distance of 20 cm from it.find the focal length of the lens.
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length formed by=20+2÷3=22÷3=7
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Answer:
m= - v / u = H.i /H.o ........ f = uv/(u+v)
m= -v/-20 = (2/(3×h.o))×h.o
m == > v /20 = 2/3
m ==> v = 40 /3
........
f = (20(40/3))/(20+(40/3))
f = (20(40/3))/(20(1+(2/3)))
f= (40/3)/ (5/3)
f = 8 cm
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