19. The radius of the convex surface of plano- convex lens is 20cm and the refractive...

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19. The radius of the convex surface of plano- convex lens is 20cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is 1. 30 cm 2. 50 cm 3. 20 cm 4. 40 cm 20. After a time equal to four half lives, the amount of radioactive material remaining undecayed is- 1. 6.25% 2. 12.50% 3. 25.0% 4. 50,0% 14. Slope of Vo - v curve is (Vo is stopping potential, v is frequency in photoelectric experiment) (1) e (3) $o (4) h 19. The radius of the convex surface of plano- convex lens is 20cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is 1. 30 cm 2. 50 cm 3. 20 cm 4. 40 cm 20. After a time equal to four half lives, the amount of radioactive material remaining undecayed is- 1. 6.25% 2. 12.50% 3. 25.0% 4. 50,0% 14. Slope of Vo - v curve is (Vo is stopping potential, v is frequency in photoelectric experiment) (1) e (3) $o (4) h