JAMB UTME - Physics - 2005

When impurities are added to semi-conductors, the conductivity of the semi-conductor

Answer Details

When impurities are added to semiconductors, a process called doping, the conductivity of the semiconductor increases. This is because impurities such as boron and phosphorus can either create additional positive or negative charge carriers in the material, thereby increasing the number of charge carriers available for conduction. The added impurities can also change the electronic properties of the material, making it easier for electrons to move through the crystal lattice. This increased conductivity allows the semiconductor to be used in electronic devices, such as transistors and diodes, where its electrical properties can be carefully controlled to perform specific functions. Therefore, the correct option is: increases.

If the distance between two point charges its increased by a factor of four, the magnitude of the electrostatic force between them will be

Answer Details

According to Coulomb's law, the electrostatic force between two charges is inversely proportional to the square of the distance between them. Therefore, if the distance between two charges is increased by a factor of four, the force between them will decrease by a factor of 16 (4^2). Therefore, the answer is: 1/16 of its former value.

The process whereby a liquid turns spontaneously into vapour is called?

Answer Details

The process whereby a liquid turns spontaneously into vapor is called evaporation. This process occurs when the molecules at the surface of a liquid gain enough energy to break away from the liquid and become vapor. Evaporation is different from boiling, which occurs when a liquid is heated to its boiling point and the entire liquid turns into vapor. In evaporation, the liquid can turn into vapor even at temperatures below its boiling point, as long as the molecules at the surface of the liquid gain enough energy to break away and become vapor. Examples of evaporation include the drying of clothes on a clothesline, the formation of dew on grass in the morning, and the evaporation of sweat from our skin.

When very hot water is poured into two identical thin and thick glass tumblers in equal volumes, the thick one cracks because?

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The thick glass tumbler cracks because of the uneven expansion of glass. When very hot water is poured into the glass tumbler, the inner layer of the glass heats up and expands faster than the outer layer. The thick glass tumbler has a larger volume than the thin glass tumbler, so the difference in expansion between the inner and outer layers is greater, which leads to uneven expansion and eventually causes the glass to crack. Glass is not a crystal, but it is a poor conductor of heat, which means it doesn't conduct heat as easily as metal, for example. However, this doesn't prevent the uneven expansion of glass when exposed to a sudden change in temperature.

A body of mass 36kg falls through a viscous liquid which offers a drag force of 260N on the body. The upthrust on the body at terminal velocity is?
[g = 10ms2]

Answer Details

For anybody falling through a viscous liquid, at its terminal velocity. the resultant force acting on its is zero. from the equation: Mg - v - u = 0. where v = viscous drag
U = upthrust Mg = weight of the body.
∴ 36 x 10 - 260 - U = 0
∴ U = 360 - 260 = 100N
Upthrust on the body = 100N.

${}_{92}^{235}U{+}_0^{1}n{\to }_{56}^{144}Ba{+}_{36}^{90}Kr+2X$

In the reaction above, X is

Answer Details

235U + 1n → 144Ba + 90Kr + 2x9205636
In the reaction above, balancing the left with the right, show that X is neutron

106J of heat is required to boil off completely 2kg of a certain liquid. Neglecting heat lost to the surroundings, the latent heat of vaporization of the liquid is

Answer Details

The latent heat of vaporization of a substance is the amount of heat energy required to completely vaporize a unit mass of the substance at constant temperature and pressure, without a change in temperature. In this case, 10^6 J of heat energy is required to completely vaporize 2 kg of the liquid. We can find the latent heat of vaporization using the formula: Latent heat of vaporization = Heat energy required / Mass of substance Therefore, the latent heat of vaporization of the liquid is: 10^6 J / 2 kg = 5 x 10^5 J/kg So, the correct option is "5.0 x 10^5 J/kg".

In the circuit diagram of a transistor above, the terminal P, Q and R represent

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In the circuit diagram of a transistor, the terminals P, Q, and R represent the emitter, base, and collector, respectively. The transistor is a three-layer semiconductor device that is used to amplify and switch electronic signals. The emitter is the terminal that emits current carriers, while the collector is the terminal that collects them. The base controls the flow of current carriers between the emitter and the collector by acting as a gate. When a small current flows into the base, it causes a much larger current to flow between the emitter and the collector, making the transistor useful for amplification and switching.

Satellite communication network makes use of?

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Satellite communication network makes use of radio waves. Radio waves are a type of electromagnetic radiation, which are transmitted through the atmosphere and space. These waves have a longer wavelength and lower frequency than visible light, making them suitable for long-range communication. Radio waves can be transmitted from an Earth-based station to a satellite in orbit, which then relays the signal to another location on the ground. This technology is used for various communication purposes, such as television broadcasts, telephone calls, and internet services.

In the figure above, the coefficient of static friction is 0.5. If the tension in the string is T, the acceleration of the system in motion is

Answer Details

Normal reaction R = 3 kg x 10 = 30N
coefficient of friction , μ = 0.5
∴ acting frictional force = μR = 30 x 0.5
Pulling/sliding force F = 6kg x 10 = 60N.
∴ Net downward force = ma = 60 - 15.0
=> (3 + 6)a = 45
∴ 9a = 45
a = 5m/s2

The north pole of a magnet can never be separated from the south pole because of the property knowledge as?

Answer Details

The correct answer is "magnetic dipole". A magnetic dipole refers to a pair of poles of opposite sign, which are characteristic of all magnets. These poles cannot be separated from each other, as trying to do so would simply result in the creation of two smaller dipoles, each with its own north and south pole. This property is known as magnetic attraction and is what makes magnets so useful in many applications, such as in electric motors, generators, and MRI machines. The other options listed - magnetic octopole, magnetic monopole, and magnetic quadrupole - do not describe the property that explains why the north and south poles of a magnet cannot be separated.

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According to the inverse square law, when the distance between two objects is halved, the force between them becomes four times stronger. Therefore, if a force of 200N acts between two objects at a certain distance apart and the distance is halved, the value of the force will be 4 times the original force, which is 800N. So the correct answer is option D: 800N.

Two charged particles are projected into a region where there is a magnetic field perpendicular to their velocities. if the charges are deflected in opposite directions, which of the following statements is true of the charge?

Answer Details

When a charged particle moves through a magnetic field perpendicular to its velocity, it experiences a force that is perpendicular to both its velocity and the magnetic field. The direction of the force is given by the right-hand rule, where the thumb points in the direction of the velocity, the fingers point in the direction of the magnetic field, and the palm shows the direction of the force. If two charged particles are projected into such a magnetic field and are deflected in opposite directions, this means that they experience forces in opposite directions. This can only happen if the particles have opposite charges, since opposite charges attract and like charges repel. Therefore, the statement that is true of the charge is: "the charge must be of opposite sign."

the ray which causes gas molecules to glow is known as

Answer Details

The ray which causes gas molecules to fluoresce or glow is the cathode rays

The figure above shows a plot of angles of deviation through a glass prism when light is incident at θ degrees on the prism. The incident angle that produces the minimum deviation is

Answer Details

The angle of minimum deviation in a prism occurs when the angle of incidence and angle of refraction are equal. This means that the light passes symmetrically through the prism, and the deviation is at its minimum. Looking at the graph, we can see that the angle of incidence where the deviation is at a minimum is approximately 25 degrees. Therefore, the answer is: 25o

If two inductors of inductances 3H and 6H are arranged in series, the total inductance is

Answer Details

When inductors are arranged in series, their individual inductances add up to give the total inductance. Therefore, the total inductance of two inductors of inductances 3H and 6H arranged in series can be found by simply adding their inductances. Total inductance = 3H + 6H = 9H Therefore, the total inductance of the two inductors is 9H. Hence, the correct option is: - 9.0H

A 3m3 volume of liquid W of density 200kgm3 is mixed with another liquid L of volume 7m3 and density 150kgm-3. the density of mixture is?

Answer Details

To determine the density of the mixture, we need to use the formula: density = mass/volume We can start by calculating the total mass of the two liquids, which is the sum of the masses of liquid W and liquid L: mass = density x volume For liquid W, mass = 200 kg/m^3 x 3 m^3 = 600 kg For liquid L, mass = 150 kg/m^3 x 7 m^3 = 1050 kg Total mass = 600 kg + 1050 kg = 1650 kg Next, we can find the total volume of the mixture by adding the volumes of the two liquids: total volume = 3 m^3 + 7 m^3 = 10 m^3 Now we can use the formula for density: density = mass/volume density of mixture = 1650 kg/10 m^3 = 165 kg/m^3 Therefore, the answer is option A: 165 kg/m^3.

the ray which causes gas molecules to glow is known as

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The ray which causes gas molecules to fluoresce or glow is the cathode rays

I. MeltingII. Boiling III. RefractionIV. ConductionWhich combination of the above is evident of the molecular nature of matter?

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A silicon material is dopped with an element of a certain group and an n-type semi-conductor is formed. the most likely group of the element is

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When a silicon material is doped with an element from group III of the periodic table, it creates a p-type semiconductor because group III elements have three valence electrons, and when they replace a silicon atom, they create a "hole" or vacancy in the crystal lattice, which behaves like a positively charged particle. On the other hand, when a silicon material is doped with an element from group V, it creates an n-type semiconductor because group V elements have five valence electrons, and when they replace a silicon atom, the extra electron creates a negatively charged particle called an "electron." Therefore, the most likely group of the element that was used to dope the silicon and form an n-type semiconductor is group V. Hence, the correct answer is option (I).

The process whereby the molecules of different substances move randomly is called?

Answer Details

The process described in the sentence is called "diffusion." Diffusion refers to the movement of molecules from a region of higher concentration to a region of lower concentration due to their random motion.

When the temperature difference between the wet and dry bulbs of a hygrometer is high, this indicates that

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A hygrometer measures the relative humidity, which is the amount of water vapor present in the air compared to the maximum amount that the air can hold at that temperature. The wet-bulb and dry-bulb thermometer are two types of hygrometers used to measure relative humidity. When the temperature difference between the wet and dry bulbs of a hygrometer is high, it means that the air is dry and has a low relative humidity. This is because when the air is dry, water evaporates faster from the wet bulb, causing a greater temperature difference between the two bulbs. So, the correct option is "the relative humidity is low."

The velocity of sound in air will be doubled if it's absolute temperature is

Answer Details

In general, the velocity of sound in air varies directly as the square root of temperature measured in kelvin.

That V$\propto \sqrt{T}⟹V^2\propto T.\text{Therefore}\frac{V_1^2}{T_1}=\frac{V_2^2}{T_2}\text{Thus Let}{V}_1=4m/s{T}_1=10K\text{Therefore}{V}_2=2V_1=8m/s⟹\frac{4^2}{10}=\frac{8^2}{T_2}{T}_2=\frac{64\times 10}{16}=40K{T}_2=4T_1$

Thus when the velocity of sound in air is doubled, it's absolute temperature will be quadrupled.

The electric field intensity in a place where a charge of 10-10c experiences a force of 0.4N is?

Answer Details

The electric field intensity can be calculated using the formula: E = F/Q, where E is the electric field intensity, F is the force experienced by the charge Q. Substituting the values given in the question, we have: E = F/Q = (0.4N)/(10^-10C) Simplifying this expression, we get: E = 4.0 x 10^9 NC^-1 Therefore, the electric field intensity in the given place is 4.0 x 10^9 NC^-1, which is option D.

In an a.c circuit that contains only a capacitor, the voltage lags behind the current by

Answer Details

In an AC circuit with only a capacitor, the voltage lags behind the current by 90 degrees. In other words, the voltage reaches its maximum value a quarter of a cycle (90 degrees) after the current reaches its maximum value. This is because the capacitor stores energy in the form of an electric field, which takes time to build up as the current passes through it. As a result, the voltage across the capacitor lags behind the current flowing through it.

a proton moving with a speed of 1.0 x 106ms-1 through a magnetic field of 1.0T experiences a magnetic force of magnitude 8.0 x 10-14 N. The angle between the proton''s velocity and the field is

Answer Details

When a charged particle moves through a magnetic field, it experiences a magnetic force perpendicular to both the velocity of the particle and the direction of the magnetic field. The magnitude of the magnetic force is given by the equation F = qvB sin(theta), where F is the force, q is the charge of the particle, v is the velocity of the particle, B is the magnetic field, and theta is the angle between the velocity of the particle and the magnetic field. In this problem, a proton with a speed of 1.0 x 10^6 m/s is moving through a magnetic field of 1.0 T and experiences a magnetic force of magnitude 8.0 x 10^-14 N. We can use the equation F = qvB sin(theta) to solve for the angle between the proton's velocity and the field. Rearranging the equation, we get sin(theta) = F / (qvB). Substituting the given values, we get sin(theta) = (8.0 x 10^-14 N) / [(1.6 x 10^-19 C) x (1.0 x 10^6 m/s) x (1.0 T)] = 0.005. Taking the inverse sine of both sides, we get theta = sin^-1(0.005) = 0.29°. Therefore, the angle between the proton's velocity and the magnetic field is approximately 0.29° or very close to 0°, which is almost parallel to the field. Thus, the correct answer is option (C) 30°.

An electric device is rated 2000 W, 250 v. The correct fuse rating of the device is?

Answer Details

To find the correct fuse rating, we can use the formula: Fuse rating = Power/Voltage Plugging in the given values, we get: Fuse rating = 2000 W / 250 V = 8 A Therefore, the correct fuse rating of the device is 8 A. Answer: 8 A

The charge carriers in gasses are

Answer Details

The charges carriers in gasses are the ions

The time it will take a certain radioactive material with a half-life of 50 days to reduce to 1/32of its original number is

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The half-life of a radioactive material is the amount of time it takes for half of the material to decay. In this question, the half-life is given as 50 days, which means that after 50 days, half of the material will have decayed. To find the time it takes for the material to reduce to 1/32 of its original number, we need to determine how many half-lives it will take to reach that point. 1/32 is equivalent to 2^(-5) since 2^5 = 32. So the material needs to decay 5 half-lives to reach 1/32 of its original number. Since the half-life is 50 days, it will take 50 x 5 = 250 days for the material to reduce to 1/32 of its original number. Therefore, the answer is 250 days.

The figure above shows three capacitors, 2μF, 3μF and 6μF connected in series. If the p.d across the system is 12V, the p.d, across the 6μF capacitor is

Answer Details

The effective capacitance in the circuit is given by:
1/C = 1/2 + 1/3 + 1/6 = 6/6
therefore C = 1μF or
1.0 x 10-6F.
Since C = Q/V, its implies that the charges Q, flowing in the circuit is given by Q = CV
= 1.0 x 10-6 x 12
= 12.0 x 10-6 Coulomb.
∴ P.d across the 6μF,

I. reproducibility II. SensibilityIII. High terminal capacityiv. High accuracy The quantities of a good thermometer include?

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Marching soldiers crossing a suspension bridge are usually advised to break their steps to avoid damaging the bridge owing to

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Marching soldiers crossing a suspension bridge are usually advised to break their steps to avoid damaging the bridge owing to resonance. The steps of the marching soldiers can set the bridge into vibration, and when the frequency of the bridge is equal to that of the steps of the soldiers, the resonance occurs,and at this resonance, the bridge vibrates violently with maximum amplitude, and can collapse.

A real image three times the size of an object is formed 24cm from a converging mirror. what is the focal length of the mirror.

Answer Details

for a real image 3 times the size of the object, it implies that the magnification 3 = v/u, 3 = 24/u, therefore 3u = 24, u = 8cm thus we have from the relation:m = (f)/(u)-f; that 3 = (f)/(8) - f. therefore f = 3(8-f) f = 24 - 3f ∴4f = 24; f = 6cm OR: (1)/(u) + (1)/(v) = (1)/(f).
(1)/(8) + (1)/(24) = (1)/(f)
therefore (3+1)/(24) = (1)/(f)
4/24=1/f;therefore 4f = 24
f = 6cm

If the system above is in equilibrium, the tension in the string Q is

Answer Details

If the string is in equilibrium, the the tension in the string Q = 4N + 5N = 9N

which of the following materials is a conductor?

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Among the given options, only Sodium is a conductor. Conductors are materials that allow electric current to flow through them easily. They have low resistance to the flow of electric current. Sodium is a metal and metals are generally good conductors of electricity. Glass, wax, and plastic are insulators and do not allow electric current to flow through them easily. They have high resistance to the flow of electric current.

The resistance of a pieces of wire of lenght 20m are crossed-sectional area 8 x 10 6m2is?
[Resistivity of the wire = 4 x 10-7 Ω m]

Answer Details

since resistance R = p (l)/a
= (4 x 10-7 x 20)/8.0 x 10-6
R = 1.0 Ω

The sharpness of the boundary of the shadow of an object is determined by the

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The sharpness of the boundary of the shadow of an object is determined by the rays of light passing through the object. The smaller the rays passing through , that is from a point source, the more sharp the shadow becomes, but the more the rays, that is rays from a large source, the more blurred the shadow becomes.

A thin converging lens has a power of 4.0 diopters determined its focal length.

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the power of a lens is defined as the reciprocal of the focal length ,expressed in metre.Mathematically, the power of a lens in dioptres is given by:(100)/f(in cm).
thus for lens of power of 4.0 dioptres we have that: (100)/(f) = +4.0
f= (100)/(4.0) = 25cm
= 0.25cm

In an ideal wheel an axle system, R stand for the radius of the wheel and r is the radius of the axle. the mechanical advantage is

Answer Details

The question is asking about the mechanical advantage in an ideal wheel and axle system where R is the radius of the wheel and r is the radius of the axle. The mechanical advantage in this system is given by the ratio of the radius of the wheel to the radius of the axle, which is R/r. Therefore, the answer is (D) R/r.

A car battery rated 45 A H is charged with a charger whose rating is 2.5A.How long will it take to charge the battery full?

Answer Details

To calculate the time required to fully charge a battery, we need to use the formula: Time (in hours) = (Battery capacity in Ah) / (Charger rating in A) In this case, the battery capacity is given as 45 Ah, and the charger rating is 2.5 A. Substituting the values in the formula, we get: Time (in hours) = 45 Ah / 2.5 A Time (in hours) = 18 hours Therefore, it will take 18 hours to fully charge the battery using a 2.5 A charger. Hence, the correct option is: 18 hrs.

The value of F in the figure above when in equilibrium is

Answer Details

F = $\frac{17}{sin60}=\frac{17}{0.866}$

= 20N

An object is projected for the hieght of 80 m above the ground with a velocity of 40ms-1 at the angle of 30° to the horizontal. The time of flight

Answer Details

for a body projected at an angle θ to the horizontal, the time of the flight is given by T = (2u sin θ)/g =(2x 40)x sin (30)/10 =(2 x 40) x (0.5)/10 = 4.0secs.

Am elastic material has a length of 36cm when a load of 40N is hung on it and a length of 45cm when a load of 60N is hung on it. The original length of the string is

Answer Details

For Hooke's law F = Ke

$⟹F/e=Kf1/e1=f2/e2\text{Let the original length}=t_0\text{therefore}e1=(36-t_0)cm;e2=(46-t_0)cm\text{if f1}=40N\text{f2}=60N\text{Then}\frac{40}{36-t_0}=\frac{60}{45-t_0}⟹40(45-t_0)=60(36-t_0)\text{therefore}1800-40t_{0}2160-60t_{0}60t_0-40t_0=2160-180020t_0=360t_0=18cm$

Two liquids L1 and L2 are contained in a U - tube. The height and the density of L1 are 8 cm and 103 kgm-3 respectively. If the density of L2 is 800 kgm-3, its height measured from the same level is

Answer Details

Generally, from Hares Experiment, density is inversely proportional to height
i.e h ∝1/d; → h1d1 = h2d2
∴ 8 x 103 = h2 x 800

The current in a reverse-biased junction is due to?

Answer Details

When a junction is reverse biased, a potential barrier is formed at the junction. This potential barrier prevents majority carriers from crossing the junction, so the current in a reverse-biased junction is due to minority carriers. The minority carriers (electrons in a p-type material and holes in an n-type material) can be thermally generated or arise from impurities. Therefore, the correct option is: minority carriers.

The pair of physical quantities consisting of vectors only are

Answer Details

The answer is displacement and torque. This is because both displacement and torque are vector quantities, meaning they have a magnitude and direction associated with them. Momentum, power, velocity, distance, acceleration, and speed are all examples of physical quantities that can be scalar or vector, but in this question, it is specified that the quantities must be vectors only.

In the figure above, the work done by the force of 100N inclined at an angle of 60o to the object dragged horizontally to a distance of 8m is

Answer Details

To calculate the work done, we need to use the formula: Work = Force x Distance x Cosine(angle) In this case, the force is 100N, the distance is 8m, and the angle is 60 degrees. We can convert the angle to radians by multiplying it by pi/180: 60 degrees x pi/180 = pi/3 radians Now we can plug in the values and solve for work: Work = 100N x 8m x Cosine(pi/3) Work = 100N x 8m x 0.5 Work = 400J Therefore, the work done by the force of 100N inclined at an angle of 60 degrees to the object dragged horizontally to a distance of 8m is 400J. The answer is option D: 400J.

A transformer is rated 240v. If the primary coil is 4000 turns and the secondary voltage 12v, determine the number of turns in the secondary coil.

Answer Details

The voltage ratio in a transformer is proportional to the number of turns in the primary coil and the number of turns in the secondary coil. Therefore, we can use this proportionality to find the number of turns in the secondary coil. The voltage ratio is 240V (primary) to 12V (secondary), which is equal to 20. So, the ratio of the number of turns in the primary coil to the number of turns in the secondary coil is also 20. We are given the number of turns in the primary coil as 4000, so we can find the number of turns in the secondary coil as follows: Number of turns in the secondary coil = (Number of turns in the primary coil) / (Voltage ratio) Number of turns in the secondary coil = 4000 / 20 = 200 Therefore, the number of turns in the secondary coil is 200.