JAMB UTME - Physics - 2020
Frage 1 Bericht
A substance has half of 3 min. After 6 min, the count rate was observed to be 400. What was its count rate at zero time?
Antwortdetails
| Let N = count rate at zero time |
| N 3min→ N 3min→ N |
| 2 4 |
| N |
| 4 |
| 400 |
| N = 400 x N |
| N/4 |
| N = 1600 |
Frage 2 Bericht
If a source of solid is moving, a stationary listener will hear a sound of different frequency. This is called?
Antwortdetails
The phenomenon you're referring to is known as the Doppler effect. Simply put, the Doppler effect is a change in the frequency of a wave (such as sound or light) as the source of the wave moves relative to an observer. For example, if a car is approaching you, the sound of its horn will seem to have a higher frequency (or pitch) than if it were stationary or moving away from you. This is because as the car moves towards you, the sound waves are compressed, causing an increase in the frequency that you hear. Conversely, if the car is moving away from you, the sound waves will be stretched out, causing a decrease in the frequency that you hear. This is why the sound of a siren on an ambulance moving away from you seems to get lower and lower as it gets further away. So in short, the Doppler effect is a change in the frequency of sound (or any other wave) that occurs when the source of the wave is moving relative to an observer.
Frage 3 Bericht
The fiqure above represents a block-and-tackle pulley system on which an effort of W Newtons supports a load of 120.0N. If the efficiency of the machine is 40 , then the value of W is
Antwortdetails
| V.E = 6, load = 120N |
| Efficiency = M.A x 1 x 100% |
| V.R |
| 40 = 120 x 1 x 100 |
| effort 6 1 |
| Effort = 50N |
Frage 4 Bericht
In the figure, the value of R is
Antwortdetails
| RT = V =12 = 6? |
| 1 2 |
| RT = 3 + R×6 |
| R+6 |
| R = 6Ω |
Frage 5 Bericht
The force required to make an object of mass m, travelling with velocity v, turn in a circle of radius r is
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Frage 6 Bericht
A convex mirror is used as a driving mirror because
I. its image is erect
II. It has a large field of view
III. It has a long focal length
Identify the CORRECT statement(s)
Antwortdetails
| A) RT = 2 + 3 + 6 = 11Ω |
| (B) RT = 3×3 = 1.2Ω |
| 2+3 |
| (C) RT = 3×2×6 |
| (2×3)+(2×6)+(3×6) |
| = 1Ω |
| (D) RT = 3 + 2×6 |
| 2+6 |
| = 4.5 Ω |
Frage 7 Bericht
The refractive index of a liquid is 1.5. If the velocity of light in a vacuum is 3.0 x 10 , the velocity of light in the liquid is
Antwortdetails
The velocity of light in the liquid can be calculated using the formula for the refractive index (n) of a medium: v = c / n, where c is the velocity of light in a vacuum and n is the refractive index of the medium. In this case, n = 1.5, so the velocity of light in the liquid would be v = 3.0 x 10^8 m/s / 1.5 = 2.0 x 10^8 m/s. Therefore, the velocity of light in the liquid is 2.0 x 10^8 m/s
Frage 8 Bericht
A few grains of table salt were put in a cup of cold water, kept at constant temperature and left undistributed. Eventually all the water tested salty. This action is due to?
Antwortdetails
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration until they are evenly distributed. It occurs in various substances, such as gases, liquids, and solids, and is driven by the random motion of molecules. This process plays a crucial role in many biological and physical phenomena, such as the movement of oxygen and carbon dioxide across cell membranes, the dispersion of perfume in the air, and the mixing of solutes in solutions.
Frage 9 Bericht
One of the following readings represents the measurement of the measurement of the length of a metal rod using vernier callipers. Taking the reading accuracy into consideration, the most likely one is
Antwortdetails
The most likely reading for the length of a metal rod using vernier callipers would be 5.160cm. This is because vernier callipers usually have a scale with increments of 0.1mm, and 5.160cm is the closest reading to 5.16cm, which would be the smallest increment that can be accurately measured using vernier callipers.
The other options, 5.165cm and 5.0cm, may not be as accurate as they do not match up with the smallest increment that can be measured using vernier callipers.
Frage 10 Bericht
The lower and upper fixed points marked on a Mercury-in-glass thermometer are 210mm. The end of the mercury column in the tube is 49mm above the lower fixed point in a room. What is the temperature of the room in degrees Celsius?
Antwortdetails
The temperature of the room in degrees Celsius is 30.43°C.
A Mercury-in-glass thermometer works by measuring the expansion of mercury in a glass tube as the temperature increases. The lower fixed point is typically the point where the mercury is at its minimum and the upper fixed point is where the mercury is at its maximum. In this case, the lower fixed point is at 0°C and the upper fixed point is at 30°C, and the mercury is 210mm above the lower fixed point. So, the temperature of the room must be 30.43°C.
Frage 11 Bericht
Which of the following statements about defects of vision is/are CORRECT?
I. For a long sighted person, close objects appear blurred
II. For a short sighted person, distant objects appear blurred
III. Short sight is corrected by using a pair of converging lenses
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Frage 12 Bericht
Which of the following statements on the use of X-rays is incorrect? X-rays are used
Antwortdetails
The statement that is incorrect is "In detecting fingerprints". X-rays are not used for detecting fingerprints. X-rays are used for obtaining images of tissues and bones inside the body, for the treatment of malignant growths like cancer cells, and to reveal hidden flaws in metal castings and welded joints in works of art. Fingerprints are usually detected using techniques like fingerprint scanning or live-scan biometrics.
Frage 13 Bericht
What is the cost of running five 50W lamps and four 100W lamps for 10 hours if electrical energy costs 2 Kobo per KWh?
Antwortdetails
P = (5 x 50) + (100 x 4)
= 650watts
Energy(kWhr) = 650 x 10-3 x 10
= 6.5 kWhr
1kWhr cost 2 kobo ; 6.5 kWhr will cost 2×6.512×6.51
= 13 kobo
Frage 14 Bericht
In what range of temperature is the expansion of water anomalous?
Antwortdetails
The expansion of water is anomalous between 0°C to 4°C. This means that in this temperature range, the density of water actually decreases as the temperature increases. This is different from most substances, which typically become less dense when they are heated and expand. The anomalous behavior of water in this temperature range makes it a critical factor in many biological and physical processes on Earth.
Frage 15 Bericht
The effect of closing the key K in the circuit shown in the figure above would be to?
Antwortdetails
| When K is open, the total Resistance = 8 + 2 = 10? |
| 1 = V? = 6v? = 0.6A |
| When K is closed, 18+18=1? |
| 28=1? |
| ? = 82 = 4? |
| ? = 82 = 4? |
| 4? in series with 2?= 6? |
| 1 = V? = 66 = 1A |
| 1 - 0.6A = 0.4A |
| Hence, 0.4A increase |
Frage 16 Bericht
In an experiment in which molten naphtha-line is allowed to cool, the cooling curve i n the figure was obtained. The temperature 80 0c is known as the
Antwortdetails
Frage 17 Bericht
Heat is supplied uniformly at the rate of 100W to 1.0 x 10-2 kg of a liquid for 20 seconds. If the temperature of the liquid rises by 5 0c, then the specific heat capacity of the liquid is
Antwortdetails
| Heat energy = Electrical Energy |
| Hence, |
| MCθ = power x time |
| 5 x 1 x 10−2 x C = 100 x 20 |
| C = 200 |
| 5×102 |
| = 4 x 104 J/kg/oC |
Frage 18 Bericht
Which of the following conditions are necessary and sufficient for total internal reflection to take place at the boundary between two optical media?
I. Light is passing from optical denser medium to optically less dense medium
II. Light is passing from optically less dense medium to optically denser medium to optically denser medium
III. Angle of incidence is greater
IV. Angle of incidence is lesser
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Frage 19 Bericht
A solid weighs 4.8g in air, 2.8g in water and 3.2g in Kerosine. The ratio of desity of the solid to that of the kerosine is
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Frage 20 Bericht
A magnetic needle is suspended first at the earth's north magnetic pole and then at a point on the magnetic equator. The respective angles between the needle and the horizontal are
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Frage 21 Bericht
The mass of a proton is approximately equal to that of
Antwortdetails
The mass of a proton is equal to that of the hydrogen atom. A hydrogen atom consists of one electron and one proton.
Frage 22 Bericht
Consider the three forces acting at O and in equilibrium as shown in the figure. Which of the following equations is/are CORRECT?
| I. P1 sin ?1 = p1 cos ?2 |
| II. P3 = P1 cos ?4 + P2cos2 |
| III. P1 sin ?1 = p2 sin ?2 |
Antwortdetails
From ?ABC
P = P1 cos ? From ACD
|
Frage 23 Bericht
A hydrometer is an instrument for measuring the
Antwortdetails
A hydrometer is an instrument for measuring the relative density of a liquid by the method of flotation. A hydrometer works by measuring the weight of a liquid in relation to the weight of an equal volume of water. The relative density of a liquid can be determined by floating the hydrometer in the liquid and measuring the level at which it floats. The hydrometer is calibrated so that the level at which it floats indicates the relative density of the liquid. The relative density of a liquid is important because it can affect the behavior of the liquid, such as its ability to mix with other liquids, its ability to dissolve solids, and its behavior under different conditions, such as temperature and pressure. Understanding the relative density of a liquid is important in many industries, including the chemical, pharmaceutical, and food industries.
Frage 24 Bericht
Two drivers G and H are at depths 20m and 40m, respectively below the water surface in a lake. The pressure on G is O1 while the pressure on H is P , If the atmospheric pressure is equivalent to 10m2 of water, then the value of P1 /P 2 is
Antwortdetails
The pressure at a depth h below the surface of a liquid can be calculated using the equation: P = P_atmosphere + ρgh where P_atmosphere is the atmospheric pressure, ρ is the density of the liquid, g is the acceleration due to gravity, and h is the depth below the surface. Given that the atmospheric pressure is 10m^2, the pressure at a depth of 20m and 40m below the surface of the lake would be: P1 = 10 + ρgh = 10 + 1000 * 9.8 * 20 = 10 + 1960 P2 = 10 + ρgh = 10 + 1000 * 9.8 * 40 = 10 + 3920 So, P2 / P1 = 3920 / 1960 = 2.00 Therefore, the value of P2 / P1 2 is 2.00.
Frage 25 Bericht
Which of the following can be described as high tension transmission?
Antwortdetails
High tension transmission refers to the transmission of electrical power at high voltage levels. High voltage allows for the transmission of electrical power over long distances with reduced losses, as less current is needed to transmit the same amount of power at high voltage. Therefore, high tension transmission can be described as high voltage and low current. This corresponds to: Low current and high voltage. In contrast, low tension transmission refers to the transmission of electrical power at low voltage levels, typically in the range of 110-240 volts. This type of transmission typically requires higher current levels to transmit the same amount of power.
Frage 26 Bericht
If in a simple pendulum experiment the length of the inextensible string is increased by a factor or four, its period is increased by a factor of?
Antwortdetails
The period of a pendulum is the time it takes for one complete cycle of swinging back and forth. The period of a simple pendulum is determined by the length of the pendulum and the acceleration due to gravity. If the length of the pendulum is increased by a factor of four, then the period of the pendulum will also increase by a factor of two. This is because the period of a simple pendulum is proportional to the square root of its length. So, if the length of the pendulum is increased by a factor of four, the period will increase by a factor of the square root of four, which is equal to two. Therefore, the answer is 2.
Frage 27 Bericht
In the study of Physics, temperature and heat are often confused with each other. Which of the following statements correctly defines these two elements?
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Frage 28 Bericht
Two mirrors of the same length are arranges as show in the diagram. A ray of light NO strikes the system at O and emerges along PQ. The emergent ray has been deviated through
Antwortdetails
| Angle of deviation = ?1+?2 = 50 + 50 + 40 + 40 |
| = 180o |
Frage 29 Bericht
The linear expansivity of brass is 2 x 10 -5 . If the volume of piece of brass is 2 x 10cm at 0 C. What will be its volume at 100 C?
Antwortdetails
| 3 x α = V2−V1 |
| V1×Δθ |
| 3 x 2 x 10−5 = V2−10 |
| 100×10 |
| V2 = (100 x 10 x 3 x 2 10−2) + 10 |
| = 10.6 cm3 |
Frage 30 Bericht
Which of the following pairs is NOT part of the electromagnetic spectrum?
I. Radio waves
II. Beta rays
III. Gamma rays
IV. Alpha rays
Antwortdetails
The pair that is NOT part of the electromagnetic spectrum is IV. Alpha rays. The electromagnetic spectrum includes different types of electromagnetic radiation, such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Alpha rays are not part of this spectrum, but are instead a type of particulate radiation made up of helium ions. So the correct answer is "II and IV".
Frage 31 Bericht
Under which of the following conditions is work done?
Antwortdetails
Because work is done = force applied × distance.
Frage 32 Bericht
A ship travelling towards a cliff receives the echo of its whistle receives the echo of its whistle after 3.5 seconds. If the speed of sound in air under the prevailing conditions is 250ms , how much closer is the ship to the cliff?
Antwortdetails
Difference in time = 1 sec
Echo time = 1 / 2 = 0.5 sec
Difference of cliff from ship = 0.5 x 250
= 125m
Frage 33 Bericht
A transformer has 300 turns of wire in the primary coil and 30 turns in the secondary coil. If the input voltage is 100 volts, the input voltage is
Antwortdetails
The voltage in the secondary coil of a transformer is proportional to the ratio of the number of turns in the secondary coil to the number of turns in the primary coil. Since the secondary coil has 30 turns and the primary coil has 300 turns, the voltage in the secondary coil will be 1/10th of the voltage in the primary coil. Therefore, if the input voltage is 100 volts, the output voltage in the secondary coil would be 100 / 10 = 10 volts.
Frage 34 Bericht
Natural radioactivity consists of emission___
Antwortdetails
Radioactivity is the spontaneous emission of radiation from atomic nuclei. This radiation can consist of alpha, beta, and gamma radiation.
Natural radioactivity is a purely nuclear phenomenon. The nucleus of a radioactive substance is unstable and such an unstable nucleus undergoes spontaneous breakdown (disintegration). The process continues until a stable nucleus is obtained.
Frage 35 Bericht
Which of the following instruments consumes the highest current?
| I. Electric iron | 250v | 1kW |
| II. Television set | 220v | 110W |
| III. Torch light | 6v | 30W |
| IV.Immersion heater | 110v | 500W |
Antwortdetails
Frage 36 Bericht
A machine gun with a mass of 5kg fires a 50g bullet at a speed of 100 ms . The recoil speed of the machine gun is
Antwortdetails
| MaVa = MbVb |
| 5 x Va = 0.05 x 100 |
| Va = 1m−1 |
Frage 38 Bericht
Which of the following statements about radioactivity is true?
(i) Alpha particle is positively charged
(ii) Beta particle is negatively charged
(iii) Gamma ray is neutral
(iv) Beta particle has the same mass as helium atom
(v) Gamma ray is charged.
Antwortdetails
The correct answer is i, ii, iii only. Alpha particles are positively charged, beta particles are negatively charged, and gamma rays are neutral. Alpha particles are made up of two protons and two neutrons, while beta particles are high-energy electrons. Gamma rays are high-energy photons and have no charge. The mass of a beta particle is not the same as that of a helium atom. Gamma rays cannot be charged, as they are photons and photons are neutral.
