By what factor will the size of an object place... - JAMB Physics 2003 Question
By what factor will the size of an object placed 10cm from a convex lens be increased if the image is seen on a screen placed 25cm from the lens?
A
15.0
B
2.5
C
1.5
D
0.4
correct option: b
Form the lens formula = 1/U + 1/V = 1/f
=> 1/10 + 1/25 = 1/f;
∴ (5 + 2) / 50 = 1/f
∴ f = 50/7cm
since the image is observed on a screen, it is a real image. Thus magnification
M = f/U-f
= 50/7 x 7/20 = 2.5
=> 1/10 + 1/25 = 1/f;
∴ (5 + 2) / 50 = 1/f
∴ f = 50/7cm
since the image is observed on a screen, it is a real image. Thus magnification
M = f/U-f
| = | __50/7 |
| 10 - 50/7 |
| ∴ M = | 50/7 |
| 20/7 |
= 50/7 x 7/20 = 2.5
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