JAMB UTME - Physics - 2011

The capacitance of a parallel plate capacitor is 20 μf in air and 60 μf in the presence of a dielectric. What is the dielectric constant?

Maelezo ya Majibu

Dielectric constant = (c)/c° = (60)/20 = 3

A certain far - sighted person cannot see object that are closer to the eye than 50 cm clearly. Determine the power of the converging lens which will enable him to see at 25 cm

Maelezo ya Majibu

V = - 50, U = 25CM
(1)/r = (1)/v + (1)/u = (1)/-50 + (1)/25 = (1 + 2)/50 = (1)/50 f = +50cm = +0.5m
p = (1)/r = (1)/0.5 = (10)/5 = 2 diopters
The power of a lens is the reciprocal of the focal length in meters. it is expressed in diopters.

Two inductors of inductance 4 II and 8 II are arrange in series and a current of 10 A is passed through them. What is the energy stored in them?

Maelezo ya Majibu

Effective inductance
(1)/L = (1)/4 + (1)/8 = (3)/8
∴ L = (8)/3
Energy stored = (1)/2 LI2
= (1)/2 x (8)/3 x 10 x 10 = (400)/3 = 133.3 J

Two balls X and Y weighing 5 g and 50 kg respectively were throne up vertically at the same time with a velocity of 100 ms1 .How will their positions be one second later?

Maelezo ya Majibu

v2 = U2 - 2G s
0 = 1002 - 2 x 10 x s = 10000 - 20s
s = (10000)/20 = 500m
Which is independent of mass.the two bodies where acted upon by the same retarding force of gravity which is independent of mass of the body; therefore both will be 500 m from the point of throw.

Steam burn is more severe than that of boiling water because

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The specific latent heat of vaporization of steam is 2.1 x 106JKg-1
while the energy required to raise the temperature of a unit mass of water from 0°c to 100°c = C x Dt = 4200 x 100 = 420000 = 4.2 x 105 JKg-1
? steam possesses greater heat energy per unit mass

If a tube of small radius opened at both ends is placed in a liquid, the liquid will

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The liquid will rise up the capillary if it wets glass and falls below its wets glass and falls below its initial level if it does not wet glass

When a red rose flower is observed in blue light, what colour does the observer see?

Maelezo ya Majibu

The colour which an object presents to the eye is the colour of light it reflects. Red rose flower will therefore absorb any other colour and reflect red. Therefore when viewed in blue light, it has no colur to reflect and will therefore appear black. Although mixture of red light and blue light = magenta . NO correct option.

An object weighs 22 kg in water and 30kg in air. what is the upthrust exerted by the liquid on the object.
[g = 10 ms2]

Maelezo ya Majibu

upthrust = weight in air - weight in liquid = 30 x 10 - 22 x 10 = 300 - 220 = 80 N

A perfect emitter or absorber of radiant energy is a

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Dull, black surface are good emitters or absorbers of energy

A man standing on a lift that is descending does not feel any weight because

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The resultant force acting on the man is given by w = mg - R
Mg - mg = 0
The man feels weightless because the reaction, R is equal to the weight mg

The bond between silicon and germanium is

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The ground is always cold at night because the

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The earth radiate heat to the atmosphere at night thereby lowering the temperature of the ground

A metal of volume 40 cm3 is heated from 30 °c to 90 °c, the increase in volume is

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increase in volume, DV = RV1 ∆ θ = 3α Vsub>1 Dθ
= 3 x 2.0 X 10-5 x 40 x (90 - 30)
= 6 x 10-5 x 40 x 60
0.144 cm3
∴ No correct option

If the threshold frequency for tungsten is 1.3 x 1015Hz, what is its work function?
[H = 6.6 x 10-34 Js]

Maelezo ya Majibu

Work function, w = hfo 6.6 x 10-34 x 1.3 x 1015
= 8.58 x 10-19

In measuring high frequency a.c, the instrument used is the

Maelezo ya Majibu

Hot wire ammeter is used because the heat affect of A C is same as that of DC

A cannon is fired from town X,after how long is the sound heard at a town Y 4.95 km away?

[velocity of sound in the air = 330 ms-1]

Maelezo ya Majibu

V = (2X)/t
330 = (2 x 4.95 x 103)/t
t = (9.9. x 103/330 = (9900)/330 = (90)/3
= 30 secs

Which of the following materials has an increase in resistance with temperature?

Maelezo ya Majibu

Resistance in metals are proportional to temperature

If it takes an object 3s to fall freely to the ground from a certain height, what is the distance covered by the object?

Maelezo ya Majibu

S = (1)/2gt2
S = (1)/2 x (10)/1 x 32 =5 x 9 = 45 m

Under which of the following conditions do gases conduct electricity?

Maelezo ya Majibu

Under high potential difference and low pressure gases are good conductor of electricity

The bond between silicon and germanium is

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I. change of state

II. Diffusion

III. Radiation

IV. Osmosis

Which of the processes above can be explained using the kinetic theory?

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A copper wire was subjected to a tensile stress of 7.7 x 107 x 10 Nm-2. calculate strain of the wire.
[young modules = 1.1 x 1011 Nm-2]

Maelezo ya Majibu

Young modules = $\frac{\text{Tensile stress}}{\text{Tensile strain}}$

= $1.1\times {10}^{1}1=\frac{7.7\times {10}^7}{\text{Tensile Strain}}$

∴ Tensile strain = $\frac{7.7\times {10}^7}{1.1\times {10}^{1}1}$

= $7.0\times {10}^{7-11}=7.0\times {10}^{-4}$

If the volume of a gas increases steadily as the temperature decreases at constant pressure, the gas obeys

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The diagram above shows two vectors at right angles to each other. The value of the resultant vector is

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The resultant, R is given by pythagoras rule, R2 = P2 + Q2
= 62 + 82 = 36 + 64 = 100
R = √100 = 10.0N

Two resistors 5Ω and 10Ω are arranged first in series and later in parallel to a 24V source, the ratio of total power dissipated in the series and parallel arrangements respectively is

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Which of the following will be applied when a metal Y is used to electroplate another metal X in electrolysis?

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Metals and hydrogen are deposited at the cathode, while non-metals and oxygen are deposited on the anode
∴ metals Y will form the anode which is deposited at the cathode made of x

In the circuit above, three resistors, 2Ω, 4Ω and 12Ω are connected in parallel and a 12V battery is connected across the combination. The current flowing through the 12Ω resistors is

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The eclipse of the sun occurs when the

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Eclipse of the sun occurs when the moon which is opaque objects between the sun and the earth

The electrical properties of germanium can be altered drastically by the addition of impurity. This process is referred to as

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The correct expression for the potential at a point distance r from a charge q in an electric field is

Maelezo ya Majibu

Electric potential is work done in taking a unit mass or charge from infinity to that point

Three similar cells each of e.m.f 2 v and internal resistance 2Ω are connected in parallel, the total e.m.f and total internal resistance are respectively

Maelezo ya Majibu

Total energy in parred connection is equal to emt of one cell, = 2v but total internal resistance is given by
(1)/r = (1)/r1 + (1)/r2 + (1)/r3 = (1)/2 + (1)/2 + (1)/2 = (3)/2
∴ r = (2)/3 = 0.67Ω

A machine is used to lift a load of 20 N through a height of 10 m. if the efficiency of the machine is 40%, how much work is done?

Maelezo ya Majibu

Efficiency = $\frac{\text{work output}}{\text{work input}}\times \frac{100}{1}$

= 40 = $\frac{20\times 10}{x}\times \frac{100}{1}$
= 500J

The diagram above show the positions of a cone. The position which can be described as neutral equilibrium is represented as

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Under neutral equilibrium, the body rolls and the position of the center of gravity , C. G is neither raised nor lowered

A carpenter on top of a roof of 20.0m high dropped a hammer of mass 1.5 kg and it fell directly to the ground. the kinetic energy of the hammer just before hitting the ground is?

[g = 10 ms-2]

Maelezo ya Majibu

K e just before hitting the gound
= P e at the maximum height (conservation of mechanical energy)
K e = P e = mgh = 1.5 x 10 x 20
= 300 J

I. High thermal capacity.

II. High sensitivity.

III.Easy readability.

IV. Accuracy over a wide range of temperature

From the statement above, the qualities of a good thermometer are

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A good thermometric liquid should not have a high thermal capacity so that the themperetue of the body being measured will not be affected
? II, III and IV are qualities of a good thermometer

In homes, electrical appliances and lamps are connected in parallel because

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The voltage of a circuit is the same whether in parallel or in series. Parallel and series affects resistance and current. So the answer should be it uses less current.

A radioactive isotope has a decay constant of 10-5s4. Calculate half life

Maelezo ya Majibu

T (1)/2 = (0.693)/λ = (0.693)/10-5
= 0.693 x 105
= 6.93 x 104 sec

Which of the following types of waves needs a medium for propagation?

Maelezo ya Majibu

Sound is the only mechanical wave among the rest which are electromagnetic waves.

A length of wire has a frequency of 255Hz when stretched by a force of b225N. If the fore increased to 324N, what is the new frequency of vibration

Maelezo ya Majibu

f1 = 255Hz, T1 = 225N
f2 = ? T2 = 324N
But f ∝ √T => f = K√T
=> K = f/√T
∴ f1/√T1 = f2/√T2225/√225 = f2/√324

When the human eye loses its power of accomodation, the defect is known as

Maelezo ya Majibu

presbyopia is loss of accommodation

A block of aluminum is heated electrically by a 25 W heater. if the temperature rises by 10°C in 5 minutes, the heat capacity of the aluminum is?

Maelezo ya Majibu

Heat supplied = Heat gained
P x t = C ∆ Ø
(25 x 5 x 60)/300 = 750 JK-1

If the charge of electricity is K wh is N4, what is the cost of operating an electrical appliance rated 250 v,2 A for six hours?

Maelezo ya Majibu

Energy consumed = power x time = lvt = 2 x 250 x 6hr = 300 wh = 3 kwh but 1 kwh = N4
3 kwh = 3 x N4 = N 12

Which of the following electromagnetic waves has the highest frequency?

Maelezo ya Majibu

r - rays has the highest frequency followed by X - rays, ultraviolet ray, visible light intra - red and the least is radio weaves

The phenomenon that shows that increase in pressure lowers the melting point can be observed in

Maelezo ya Majibu

Regelation means refreezing a phenomenon whereby melted ice free from increased pressure refreezed when they are released from the pressure.

I. Density of the liquid.

II. Depth below the surface of the liquid.

III. Surface area of the liquid.

In which of the statement above will pressure be dependent?

Maelezo ya Majibu

Pressure in liquid is independent of cross sectional area of the container/ liquid
∴ the correct options are I & II

Which of the following is a property of steel?

Maelezo ya Majibu

Steel is not easily magnetized and dismagnetized

Which of the following could be effectively used to reduce friction?

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grease is more viscous than the rest of the liquids

In an A.C circuit, the ratio of r.m.s value to peak value of current is

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An image in a convex lens is upright and magnified 3 times. If the focal length of the lens is 15 cm, what is the object distance?

Maelezo ya Majibu

m = v/u = -3
v = -3u
f = 15cm
1/v + 1/U = 1/f1/-3U + 1/u = 1/152/3u = 1/15
3U = 15 x 2
U = 30/3
= 10 cm

An object of mass 2 kg moves with a velocity of 10 ms1 round at circle of radius 4 m. Calculate the centripetal force on the object

Maelezo ya Majibu

Centripetal force,
F = $\frac{m{v}^2}{r}$
= $\frac{2\times {10}^2}{4}$
= $\frac{200}{4}$= 50N