2004 - JAMB Physics Past Questions and Answers - page 1

Current (I) = ^q/_t → q = i x t

= 16 x 10^-3 x 1

= 1.6 x 10^-2C

But 1.6 x 10^-19C = I electronic charge

1 coulomb = 1 / (1.6x10^-19)

∴ 1.6 x 10^-2 coulombs = 1 / (1.6x10^-19) x 1.6x10^-2 / 1

= 1.0 x 10^-2 x 10¹⁹

= 1.0 x 10¹⁷

¹/_C = ¹/_0.3 + ¹/_0.5 + ¹/_0.2 = 10.3333

=> C = 1 / 10.3333 = 0.09677

≅ 0.1μF

∴ C = 0.1μF

In order to protect a material from the influence of an external magnetic field, the material is placed in a soft iron ring, usually referred to as magnetic screening.

Power, P = I²R;

and I = ^E/_R

But effective Parallel resistance: is given by:
¹/_R = ¹/₆ + ¹/₃ = ¹⁺²/₆ = ³/₆ => R = ⁶/₃ = 2Ω

Current I = ^E/_R = ¹²/₂ = 6A

But I₁ = (^R₁/_R1+R2) x 1 = ³/₉ x 6 = 2A

again I₁ = (^R₁/_R1+R2) x 1 = ⁶/₉ x 6 = 4A

∴P₁ = I₁² R₁ = 2 x 2 x 6 = 24W

P₂ = I₂² R₂ = 4 x 4 x 3 = 48W

thus ^P₁/_P2 = ²⁴/₄₈ = ¹/₂ ; OR P₁ : P₂ = 1:2

K.E = ¹/₂MV²

Force, F = ma => a = ^F/_m = ¹²/₄ = 3ms^-2

But a = (V-U) / t => V = u + at

If the initial velocity U = 0, then V = at = 3 x 3 = 9ms^-2

∴ K.E, = ¹/₂ms^-2
1/₂ 4 x 9 x 9 = 162J

efficiency = (M.A / V.R) x 100/1 => ⁶⁰/₁₀₀ = ^M.A/₅

∴M.A = (60 X 5) / 100 = 3

But M.A = Load/Effort; => 3 = Load/500

∴Load = 500 x 3

= 1500N