2010 - JAMB Physics Past Questions and Answers - page 4

pumping out of the gas in the discharge tube reduces the pressure inside the tube, therefore, electricity is conducted at low pressure

Correct Answer: Option E

        ∆E = hf <br />

f = (∆E)/h = (5.44 x 10^-19)/6.6 x 10^-34 = 8.24 x 10¹⁴

transistor serve the same purpose as triode valve, which is amplification of signals.

A semiconductor is a material whose conductivity is between good conductor and insulator. Example of pure semi conductors are silicon and germanium

Above are the V-t graphs for

I Uniform acceleration

II uniform retardation

III Uniform velocity

Thus the car has no acceleration between point F and G since that portion of the graph represents uniform velocity

A bod y is said to be in stable equilibrium if after a slight displacement, the body returns to its former position. Thus, position III, VI and XI represents position of stable equilibrium

Length of the string

L = y + x = 0.5m

∴ x = L - y

= distance moved in the direction of force (which is the weight) when the body is released But cos 60^o = ^y/_0.5

∴ y = 0.5cos60 = 0.5 x ¹/₂ = 0.25

∴ x = l - y = 0.5 - 0.25 = 0.25m

Work done = force x distance moved in the direction of force.

= 0.1 x 0.25 = 0.0252J

Metals P, Q

original length lP, lQ

Increase in length ΔlP, ΔlQ

Linear expansivities αP, αQ

∴ ^αP/_αQ = ²/₃ ; and ^lP/_lQ = ³/₄

But increase in length, Δl = αlΔθ

∴ΔlP = αPlPΔθ

ΔlQ = αQlQΔθ

∴ Ratio of increase in length of P to Q = 1:2

The velocity of sound in air, V∝√T, where T is absolute temperature

Thus V = K√T or K = ^V/_T

V is independent of pressure and density at a fixed temperature.

∴ ^V₁/_√T1 = ^V₂/_√T2

T₁ = 16 + 273 = 289K, V₁ = 340ms^-1

T₂ = 127 + 273 = 400K, V₂ = ?

= 400m/s

C = C1 + C2 + C3

= 2 + 4 + 8 = 14μF

V = 6V

Energy = ¹/₂CV^2
1/₂ x 14 x 10^-6 x 6²

= 2.52 x 10^-4 J