A plano convex lens has a maximum thickness of 1mm. If diameter of aperture is 8cm then focal length
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see figure, here it is shown that A plano convex lens of thickness 1mm and diameter of its aperture is 8cm or 80mm.
so, AB = radius of aperture = 40mm
PC = radius of curvature = R
then, BC = (R - 1) mm
and AC = radius of curvature = R
use Pythagoras theorem,
AC² = AB² + BC²
R² = 40² + (R - 1)²
R² = 1600 + R² + 1 - 2R
1601- 2R = 0
R = 800.5mm
hence,
and [ because 2nd surface is plane ]
now, use formula ,
= (1.5 - 1) [ 1/800.5 - 1/∞ ]
= 0.5/800.5
= 1/1601
hence, f = 1601 mm or 160.1 cm
so, AB = radius of aperture = 40mm
PC = radius of curvature = R
then, BC = (R - 1) mm
and AC = radius of curvature = R
use Pythagoras theorem,
AC² = AB² + BC²
R² = 40² + (R - 1)²
R² = 1600 + R² + 1 - 2R
1601- 2R = 0
R = 800.5mm
hence,
and [ because 2nd surface is plane ]
now, use formula ,
= (1.5 - 1) [ 1/800.5 - 1/∞ ]
= 0.5/800.5
= 1/1601
hence, f = 1601 mm or 160.1 cm
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