JAMB UTME - Physics - 2011

A perfect emitter or absorber of radiant energy is a

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Dull, black surface are good emitters or absorbers of energy

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

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

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

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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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]

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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

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

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

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

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

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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

Under which of the following conditions do gases conduct electricity?

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

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

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?

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

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

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Resistance in metals are proportional to temperature

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

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presbyopia is loss of accommodation

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?

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

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

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

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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

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

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]

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

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

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

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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.

The bond between silicon and germanium is

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

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

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?

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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

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 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?

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

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

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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.

Which of the following is a property of steel?

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Steel is not easily magnetized and dismagnetized

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

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

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

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

Which of the following electromagnetic waves has the highest frequency?

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

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

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

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

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

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

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]

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

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

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

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

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

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?

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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.

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?

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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

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

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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]

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

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

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

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 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?

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

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

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?

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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