JAMB UTME - Physics - 2011

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?

Détails de la réponse

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

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?

Détails de la réponse

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

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

Détails de la réponse

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

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

Détails de la réponse

Resistance in metals are proportional to temperature

The eclipse of the sun occurs when the

Détails de la réponse

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

Détails de la réponse

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

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?

Détails de la réponse

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

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?

Détails de la réponse

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

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

Détails de la réponse

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

Détails de la réponse

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

Détails de la réponse

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?

Détails de la réponse

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

I. change of state

II. Diffusion

III. Radiation

IV. Osmosis

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

Détails de la réponse

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

Détails de la réponse

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

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

Détails de la réponse

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

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?

Détails de la réponse

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

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

Détails de la réponse

The ground is always cold at night because the

Détails de la réponse

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

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

Détails de la réponse

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.

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?

Détails de la réponse

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

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

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]

Détails de la réponse

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

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

Détails de la réponse

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

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

Détails de la réponse

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

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

Détails de la réponse

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

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

Détails de la réponse

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

Détails de la réponse

The bond between silicon and germanium is

Détails de la réponse

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

Détails de la réponse

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

The bond between silicon and germanium is

Détails de la réponse

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?

Détails de la réponse

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

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

Détails de la réponse

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

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

Détails de la réponse

grease is more viscous than the rest of the liquids

Steam burn is more severe than that of boiling water because

Détails de la réponse

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

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

Détails de la réponse

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

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

Détails de la réponse

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

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?

Détails de la réponse

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.

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

Détails de la réponse

presbyopia is loss of accommodation

Which of the following is a property of steel?

Détails de la réponse

Steel is not easily magnetized and dismagnetized

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]

Détails de la réponse

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 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]

Détails de la réponse

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

Détails de la réponse

Which of the following electromagnetic waves has the highest frequency?

Détails de la réponse

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

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

Détails de la réponse

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]

Détails de la réponse

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

Détails de la réponse

Dull, black surface are good emitters or absorbers of energy

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

Détails de la réponse

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

Détails de la réponse

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

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

Détails de la réponse

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 types of waves needs a medium for propagation?

Détails de la réponse

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

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

Détails de la réponse