2002 - JAMB Physics Past Questions and Answers - page 4

The iris controls the amount of light by limiting the volume of light admitted. The lens then focuses the light onto the retina, forming an inverted image. The lens changes its shape to adjust the focus on both distant and near objects, a process called accommodation.

This adjustment is done by two sets of muscles in the iris

Electric Power = IV = I²R = ^V2/_R thus for a device rated 1000 W, 230V, from the relation P = ^V2/_R, 1000 = ⁽²³⁰⁾²/_R

=> R = ⁽²³⁰⁾²/₁₀₀₀

= 52900/1000 = 52.9Ω

I = ^V/_R = 0.6E/3 = 0.2E

Again, I = E / (R+ϒ) = E / (3+ϒ)

Divide eqn (2) by eqn (1)
^I/_I = E / (3+ϒ) x I / 0.2E

=> 0.2(3+ϒ) = 1

0.6 x 0.2ϒ = 1

∴0.2ϒ = -0.6

=> ϒ = 0.6 / 0.2 = 3Ω

ϒ = 3Ω

The particle in the reaction is neutron

A photon of energy E = hf

= 6.63 x 10^-34 x 3 x 10⁵

= 19.89 x 10^-29

= 2.0 x 10^-28J

After 5 half-lives, the fraction of any radio-active substance left = (¹/₂)⁵ = ¹/₃₂

Thus the percentage of the original nuclie = ^1/32/₁ x ¹⁰⁰/₁

assuming the original amount is unity percentage left

= ¹/₃₂ x ¹⁴⁰⁰/₁ = 3.12