JAMB UTME - Physics - 2015

If an object which mass is 3kg moves in a circular path of a radius 0.7m, record a speed at 2m/s what is the result of the angular velocity?

Détails de la réponse

M= 3kg, r = 0.7m, v = 2m/s

v = wr

w = angular velocity

r = radius in an tangential circular

v = speed of an object

W = V/δ = 2/ 0.7 = 2.85

W = 2.853rads–1 (total interest whole number)

W = &approx.; 3rads–1Angular velocity (w) = 3rads–1

Lodestone is a natural magnet, it points at

Détails de la réponse

A lodestone is a natural magnet that points towards the Earth's magnetic North Pole when suspended freely. The Earth has a magnetic field that causes a lodestone to align in a North-seeking direction. When a lodestone is suspended freely, it will align itself in a way that points towards the Earth's magnetic North Pole, which is why a lodestone points towards the North-South direction. So, the correct answer is N – S when suspended freely.

If the mechanical advantage of a machine is 4. What is its ratio for LOAD to EFFORT?

Détails de la réponse

Mechanical advantage (M.A) of a machine is the ratio of its load to effort

Mathematically

Mechanical advantage (M.A) = Load (L) ÷ Effort (E)

In symbol M.A = L/E

Note:Mechanical (advantages has no S.I unit)

If M.A = 4 then,

L/E = 4/1

The ratio of load to effort = 4 : 1 respectively

A structural engineer stood on a top of a building releasing a light and heavy object to the ground which of the following statement is true?(Neglect Air Resistance)

Détails de la réponse

Assuming that air resistance is neglected, both the light and heavy objects will fall at the same rate and reach the ground at the same time. This is known as the principle of equivalence and is a fundamental principle of physics. According to this principle, the acceleration due to gravity is the same for all objects, regardless of their mass. This means that both the light and heavy objects will experience the same acceleration as they fall towards the ground. The acceleration due to gravity near the surface of the Earth is approximately 9.8 m/s^2. This means that an object in free fall near the surface of the Earth will accelerate at a rate of 9.8 m/s^2. As a result, both the light and heavy objects will fall at the same rate and reach the ground at the same time. Therefore, the answer to the question is Both light and heavy subject reach the ground at the same time.

Calculate the gravitation force of attraction between two planets of 1024kg and 1027kg separated by a distance of 1020meters.

Détails de la réponse

The gravitational force of attraction between two objects is given by the formula: F = G * (m1 * m2) / r^2 where F is the force of attraction, m1 and m2 are the masses of the two objects, r is the distance between their centers of mass, and G is the gravitational constant, which has a value of 6.67 x 10^-11 Nm^2/kg^2. In this case, we are given the masses of the two planets (10^24 kg and 10^27 kg) and the distance between them (10^20 meters). We can plug these values into the formula to calculate the gravitational force of attraction: F = (6.67 x 10^-11 Nm^2/kg^2) * ((10^24 kg) * (10^27 kg)) / (10^20 meters)^2 F = 6.67 x 10^-11 * 10^51 / 10^40 F = 6.67 x 10^11 N Therefore, the gravitational force of attraction between the two planets is approximately 6.67 x 10^11 N. ("6.67N") is the correct answer. Note: The answer may seem very large, but this is because the masses and distances involved are very large (in astronomical scales).

The resultant force of a couple is ………?

Détails de la réponse

The correct answer is "Zero". A couple is a pair of equal and opposite forces that are separated by a certain distance. The forces produce a rotational effect on an object, but do not produce any linear motion. The resultant force of a couple is always zero because the two forces are equal and opposite. This means that they cancel each other out, and there is no net force acting on the object. The rotational effect of a couple is known as torque, which is a measure of the twisting force that causes an object to rotate.

What type of electromagnetic radiation can be used to take photographs in the haze?

Détails de la réponse

Infrared rays can be used to take photographs in the haze. Infrared radiation is a type of electromagnetic radiation with longer wavelengths than visible light. This allows it to penetrate through the haze and produce images that are clearer than those taken with visible light. Infrared photography is commonly used in various fields, such as in military and law enforcement to see through the haze, smoke, and other obstructions, as well as in scientific research to study the thermal properties of objects. Radio waves, visible light, and gamma rays are not typically used to take photographs in the haze, as they are not able to penetrate through the haze as effectively as infrared radiation.

Radio waves belong to the class of wave whose velocity is about

Détails de la réponse

Radio waves belong to the class of wave whose velocity is about 3 × 10^8 m/s. Radio waves are a type of electromagnetic wave, which means they are composed of both electric and magnetic fields that oscillate at right angles to each other and to the direction of wave propagation. Like all electromagnetic waves, radio waves travel at the speed of light in a vacuum, which is approximately 3 × 10^8 m/s. This means that radio waves also travel at this speed in air and other materials, although their speed may be slightly slower in denser materials like water or metal. It's important to note that the velocity of a wave refers to the speed at which the wave propagates through a medium, which is different from the frequency and wavelength of the wave. The frequency of a wave refers to the number of oscillations per unit time, while the wavelength refers to the distance between two successive peaks or troughs of the wave. Radio waves can have a wide range of frequencies and wavelengths, which determine their properties and applications in various fields such as communication, broadcasting, and remote sensing.

If a ball released from a height of 20m, How long would it take the ball to reach the ground? (assures g = 10m/s)

Détails de la réponse

The correct answer is "2 seconds". When an object is dropped from a height, it falls under the influence of gravity, which accelerates it downwards. This acceleration due to gravity is denoted by 'g' and has a value of approximately 10 m/s^2 on the surface of the Earth. To determine how long it takes for the ball to reach the ground, we can use the following kinematic equation: d = (1/2) * g * t^2 where 'd' is the distance traveled, 'g' is the acceleration due to gravity, and 't' is the time taken. In this case, the initial height of the ball is 20 m, so we can set 'd' equal to 20 m. We know that 'g' is 10 m/s^2, so we can substitute these values into the equation to get: 20 = (1/2) * 10 * t^2 Simplifying this equation, we get: t^2 = 4 Taking the square root of both sides, we get: t = 2 Therefore, it takes 2 seconds for the ball to reach the ground. So, the correct option is "2 sec".

Neutron were discovered by

Détails de la réponse

Neutrons were discovered by James Chadwick in 1932. Before Chadwick's discovery, scientists knew that atoms were made up of positively charged protons in the nucleus and negatively charged electrons orbiting around the nucleus. However, they couldn't explain why some elements had different isotopes with varying atomic masses. Chadwick performed experiments in which he bombarded beryllium atoms with alpha particles and observed that they emitted a new type of radiation that was not deflected by electric or magnetic fields. He concluded that this radiation consisted of uncharged particles with roughly the same mass as protons, which he called neutrons. Chadwick's discovery of the neutron helped explain why some elements had different isotopes with varying atomic masses, and it paved the way for further discoveries in nuclear physics.

A stroboscope can be used to make the ware appear …………..

Détails de la réponse

A stroboscope is a device that produces flashes of light at regular intervals. By adjusting the frequency of the flashes, it is possible to make a moving object appear stationary or appear to move in slow motion or fast motion. Therefore, the correct option for the question is: - Stationary

For a best result using temperature to achieve an accurate measurement, it is best to use

Détails de la réponse

The answer is "Gas thermometer." A gas thermometer is the best option for achieving the most accurate temperature measurements. This is because gas thermometers have a very high degree of sensitivity and precision, and they can measure temperatures to a very fine degree of accuracy. Gas thermometers work by using a gas (usually hydrogen or helium) as the temperature-sensitive material. As the gas is heated or cooled, its volume changes, and this change in volume is used to calculate the temperature. Gas thermometers are often used as the standard for calibrating other temperature measurement devices. Mercury and alcohol thermometers are less accurate than gas thermometers, although they are still widely used in many applications. Clinical thermometers are specialized thermometers used for measuring human body temperature, and they are typically less precise than other types of thermometers. In summary, while all of the thermometers listed can be used for temperature measurements, a gas thermometer is the best option for achieving the most accurate and precise results.

The device in which one circuit controls another, especially if the current in the second circuit is large or dangerous is known as

Détails de la réponse

The correct answer is "Magnetic relay device". A magnetic relay is an electrical switch that is activated by a magnetic field. It's used to control a high-power or dangerous circuit using a low-power circuit. For example, you can use a low-power circuit to turn on a high-power circuit, such as turning on a large electrical motor. The low-power circuit creates a magnetic field that activates the magnetic relay, which then switches on the high-power circuit. This allows you to control the high-power circuit from a safe distance and protect yourself from potential electrical hazards.

A platinum resistance thermometer wire has a resistance of 70hms at 0°Cand 7.5 Ohms at 100°C. Calculate the temperature of the wire when the resistance is 7.2 Ohms

Détails de la réponse

R0 = 7Ω , R1 = 7.2 Ω, R2 = 7.5 Ω, Tx = ?

[(X – T100°C) ÷ (R1 - R0)] = [(T100°C – T0°C) ÷ (R2 - R0)]

[(Tx – 0) ÷ (72 – 7)] = [(100 – 0) ÷ (7.5 – 7)]

Tx/0.2 = (100 ÷ 0.5)

Tx = [(0.2 × 100)] ÷ 0.5

= 20/0.5 = 40°C

The optical instrument which is suitable for viewing a nearby objects is ………..?

Détails de la réponse

The optical instrument that is suitable for viewing nearby objects is a microscope. A microscope uses lenses to magnify small objects that are too small to see with the naked eye. It works by gathering and focusing light onto a small object, making it appear much larger. Microscopes are commonly used in scientific research, medicine, and education to examine cells, microorganisms, and other small structures. They come in various types and designs, including compound microscopes, stereo microscopes, and electron microscopes.

The compressed regions and the space-out regions in longitude wave are refers to as

Détails de la réponse

The correct answer is Compression and Rarefaction. When a longitudinal wave travels through a medium, it causes particles in the medium to oscillate back and forth parallel to the direction of wave propagation. The compressed regions are the areas where the particles are pushed closer together than their normal positions, while the rarefaction regions are the areas where the particles are spread apart more than their normal positions. These compressed and rarefied regions are collectively known as compression and rarefaction, respectively. For example, when sound waves travel through air, the compressed regions correspond to the high-pressure regions (peaks) of the sound wave, while the rarefaction regions correspond to the low-pressure regions (troughs) of the sound wave.

If an object is placed at a height of tem above the ground at a stationary point. It posses what types of energy?

Détails de la réponse

If an object is placed at a height of h above the ground at a stationary point, it possesses potential energy. Potential energy is a type of energy that is stored in an object due to its position or configuration. In this case, the object has the potential to do work by virtue of its position above the ground. The potential energy of an object at a height h above the ground is given by the formula: Potential energy = mgh where m is the mass of the object, g is the acceleration due to gravity, and h is the height of the object above the ground. As the object is at a stationary point and not in motion, it does not possess any kinetic energy. However, it possesses potential energy due to its position above the ground. When the object is allowed to fall to the ground, its potential energy is converted to kinetic energy, and it will be in motion with a velocity that depends on its mass and the height from which it was dropped. In summary, the correct answer to the given question is potential energy.

Primary colours of light are

Détails de la réponse

The answer is "Red, blue and green." The primary colors of light are the colors that can be combined to create all other colors. In contrast to the primary colors of paint or pigment (which are red, yellow, and blue), the primary colors of light are red, blue, and green. When these three primary colors of light are combined in different ways, they can produce a wide range of colors. For example, when red and green light are combined, they produce yellow. When all three primary colors are combined at equal intensity, they produce white light. The primary colors of light are important in a variety of fields, including photography, television, and computer screens, where they are used to create and display color images.

Which of the following will increases the boiling point of water?I. Taking it to a high altitude

II. Dissolving a salt into it

III. Heating it in a sealed flask

IV. Increasing the rate of heat supply.

Détails de la réponse

The boiling point of water can increase, if

1. Heating it in a sealed flask

2. The rate of the heat supply is increased

Boyle?s law may be Witten as

Détails de la réponse

The correct expression of Boyle's law is "P1V1 = P2V2". This law states that the product of the pressure and volume of a gas at a constant temperature is always constant. In other words, if you change the pressure of a gas, its volume will change in an opposite direction so that the product of the pressure and volume remains constant. For example, if you increase the pressure of a gas, its volume will decrease, and vice versa. This relationship between pressure and volume is useful in many real-world applications, such as in the design of gas storage tanks and gas transport pipelines.

The two liquids which are often used in thermometer on experiment basic is known as

Détails de la réponse

The two liquids that are often used in thermometers for experiments are mercury and alcohol. Thermometers are used to measure temperature and work by using the principle that liquids expand when they are heated and contract when they are cooled. Mercury and alcohol are both good choices for use in thermometers because they have high thermal expansion coefficients, which means that they expand and contract significantly in response to temperature changes. Mercury has been traditionally used in thermometers because it has a large thermal expansion coefficient and is a good conductor of heat. However, mercury is also toxic and can be dangerous if it is accidentally spilled or ingested. Alcohol is an alternative to mercury that is less toxic and safer to handle. Water can also be used in thermometers, but it has a lower thermal expansion coefficient than alcohol and mercury, which limits its accuracy and usefulness in some applications. In summary, both mercury and alcohol are commonly used in thermometers for experiments due to their high thermal expansion coefficients, with mercury being a traditional choice and alcohol being a safer alternative.

Convert 45°C to kelvin

Détails de la réponse

To convert Celsius to Kelvin, we add 273.15 to the Celsius temperature. Therefore, to convert 45°C to Kelvin, we simply need to add 273.15 to 45, which gives: 45 + 273.15 = 318.15 Kelvin (rounded to two decimal places) Therefore, the correct answer is: 318K.

What is the magnitude of the couple which acts on a rotating circular disc of radius 2m, if a constant tangential force of 2N is responsible for the rotation.

Détails de la réponse

The magnitude of the couple (torque) that acts on a rotating circular disc can be calculated using the equation: τ = Fr where τ is the torque, F is the force, and r is the radius. In this case, the force is 2 N and the radius is 2 m, so the torque is: τ = F * r = 2 N * 2 m = 4 Nm. So, the magnitude of the couple that acts on the rotating circular disc is 4 Nm.

A zinc has a heat capacity of 40 J/K, what is the mass of the zinc, given that the specific heat of zinc is 380 J/kg k

Détails de la réponse

We can use the formula: heat capacity = mass x specific heat capacity to find the mass of the zinc. Rearranging the formula, we get: mass = heat capacity / specific heat capacity Substituting the given values, we get: mass = 40 J/K / 380 J/kg K mass = 0.1053 kg So, the mass of the zinc is approximately 0.11 kg. Therefore, the correct option is: - 0.11kg , 3, and 4 are not correct because they are different values and do not match the result of the calculation.

What is the relationship mechanical advantage (MA) velocity Ratio (V.R) and efficiency with percentage?

Détails de la réponse

The relationship between mechanical advantage (MA), velocity ratio (V.R), and efficiency can be expressed using the equation: e = M.A/V.R × 100 %. Mechanical advantage is a measure of how much a machine can multiply force. Velocity ratio is a measure of how much a machine can multiply distance. Efficiency is a measure of how much work put into a machine is converted to useful work output. The equation e = M.A/V.R × 100 % shows that the efficiency of a machine is equal to the mechanical advantage divided by the velocity ratio, multiplied by 100%. This means that as the mechanical advantage of a machine increases, its efficiency also increases. Similarly, as the velocity ratio of a machine increases, its efficiency also increases. It's important to note that no machine can be 100% efficient, as some energy is always lost due to factors such as friction and heat. However, by understanding the relationship between mechanical advantage, velocity ratio, and efficiency, we can design and use machines in a way that maximizes their performance and minimizes waste.

The symbol −10X  used to represent which of the particles?

Détails de la réponse

The symbol -10 X is used to represent electrons. Electrons are negatively charged particles that orbit the nucleus of an atom. The negative charge of an electron is denoted by the symbol -1, and the atomic number of an element represents the number of protons in the nucleus. Therefore, the symbol -10 X represents 10 electrons. It is worth noting that this notation is often used in physics and chemistry to represent the charge and number of electrons in a system. In comparison, protons are positively charged particles found in the nucleus of an atom, and neutrons are neutral particles also found in the nucleus. Atoms are the smallest unit of matter that retains the chemical properties of an element.

At 35°C and 5 atmospheres pressure the density of a gas is 0. 600g per liter. What is the density at 7 atmospheric pressure and 350°C.

Détails de la réponse

$\theta 1=35°CT1=273+\theta =73+35=308kP1=5$atm

d1 = 0.600g/ litre

θ2 = 350°C, T2 = 2 + 3 + θ

= 273 + 350 = 623k, d2 = ?

P2 = 7atm

T a P a 1/d = TPK/d (where k is a constant)

Tp1 ÷ d1 = T1P2 ÷ d2, [(308 × 5) ÷ 0.600]

= (623 × 7) ÷ d2

d2 = (623 × 7 ×0.600) ÷ (308 × 5)

= 2616.6 ÷ 1540

= 1.69g / litresd2 = 1.69g / litres

∴ d2 = 1.70g / litres (Approx.)

The external parts of an object can be measure accurately through the use of which scientific instrument?

Détails de la réponse

Micrometer screw gauge measure an objects accurately (mainly on the external parts of the object). It measures the external parts of objects only

If the velocity ratio of a machine is 5. What is its ratio of x and y?

Détails de la réponse

Velocity Ratio (V.R) = distance moved by the effort (x)÷ distance moved by the load (y)

i.e. V.R = x/y

v. R = 5, x/y = ?

i.e x/y = 5/1; , where x = 5, y = 1

x : y = 5 : 1

Détails de la réponse

The term used to describe the direction of the path taken by light is "ray." A light ray is a thin beam of light that travels in a straight line from its source. The direction of the ray is determined by the angle at which it is emitted from the source. When the ray encounters a surface, it may be reflected, refracted or absorbed, depending on the properties of the surface. The other options, "locus," "lines," and "beam," do not accurately describe the direction of light. "Locus" refers to the set of all points that satisfy a particular condition, and "lines" can refer to a variety of things but does not specifically describe the direction of light. "Beam" refers to a group of rays, rather than the direction of a single ray. Therefore, the correct answer is: Ray.

At what respective value of a, b, and c would the unit of work, the joule, be dimensionally similar to Ma Lb Tc?

Détails de la réponse

Work (w) = Force (f) × Distance (d)

Note: f = ma = mass × acceleration

= mass ×acceleration ×distance

= kg ×ms–2 × m

= kg m2 5–2

(Note: the dimension of kg = M, M = L & S = T)

Work = ML2 T–2 = Ma Lb Tc

i.e. Ma Lb Tc = as 1, b = 2, c = –2

The value of a, band c = 1, 2, –2

A vector quantity can only be completely described when ……… and …………are mentioned.

Détails de la réponse

The answer is "Magnitude and direction." A vector quantity is a type of physical quantity that has both magnitude (size) and direction. Magnitude refers to the numerical value of the quantity, while direction refers to the path along which the quantity is moving. For example, if we want to describe the velocity of an object, we need to specify both its speed (magnitude) and the direction in which it is moving. Without knowing the direction, we cannot fully understand the velocity of the object. Similarly, for other vector quantities such as force, acceleration, and displacement, both magnitude and direction must be specified to fully describe the quantity.

The strength of an electromagnet increase with

Détails de la réponse

The strength of an electromagnet increases with an increase in the number of turns of the coil. An electromagnet is a type of magnet that is created by passing an electric current through a coil of wire. The magnetic field produced by the current in the coil causes the coil to act as a magnet, which can attract or repel other magnetic materials. The strength of an electromagnet depends on several factors, including the number of turns of wire in the coil, the amount of current passing through the wire, and the shape and material of the core used in the coil. In particular, increasing the number of turns of wire in the coil increases the strength of the magnetic field produced by the current. This is because each turn of wire adds to the magnetic field produced by the other turns, resulting in a stronger overall magnetic field. Decreasing the current in the coil or increasing the distance between the poles of the magnet will decrease its strength. Increasing the current without the coil will not result in the creation of an electromagnet because a magnetic field is produced by the flow of current through a coil of wire, not by the current itself.

Body floats in fluid when its …………………

Détails de la réponse

A body floats in fluid when it displaces its own weight of the fluid. This is known as Archimedes' principle. When an object is placed in a fluid, it experiences an upward force called buoyancy. This buoyant force is equal to the weight of the fluid displaced by the object. If the buoyant force is greater than the weight of the object, the object will float. If the buoyant force is less than the weight of the object, the object will sink. According to Archimedes' principle, an object floats in a fluid when it displaces its own weight of the fluid. This means that the weight of the fluid displaced by the object is equal to the weight of the object. So, the buoyant force acting on the object is equal to its weight, and the object floats in equilibrium. Therefore, the correct option is: - Displaces its own mass of the fluid is not correct because an object displaces its own volume of the fluid, but the weight of the fluid displaced is equal to the weight of the object, not its volume. is not correct because the object does not displace its own density of the fluid. is not correct because the object is still subjected to gravity, but the buoyant force acting on it counteracts the gravitational force and allows it to float.

Quantities of heat Q can be measured using a container called

Détails de la réponse

The correct answer is "Calorimeter". A calorimeter is a container used to measure the amount of heat involved in a chemical reaction or physical process. It's used to determine the amount of heat energy absorbed or released during a reaction. The calorimeter is designed to prevent heat loss to the surrounding environment, allowing for an accurate measurement of the heat being produced or absorbed. The measurement of heat energy is usually done in units of joules (J) or calories (cal). Calorimeters can come in various forms, including bomb calorimeters for high-pressure reactions and coffee cup calorimeters for low-pressure reactions.

The general gas law can be written as

Détails de la réponse

The general gas law can be written as PV ÷ T = a constant. The general gas law, also known as the combined gas law, relates the pressure (P), volume (V), and temperature (T) of a gas. It states that the product of the pressure and volume of a gas divided by its temperature is a constant value. Mathematically, this is expressed as PV ÷ T = a constant. This means that if you increase the pressure of a gas while keeping the temperature and volume constant, the volume will decrease. Similarly, if you increase the temperature of a gas while keeping the pressure and volume constant, the volume will increase. The general gas law is a very useful tool for understanding the behavior of gases and predicting how they will behave under different conditions.

If a projectile has maximum range of 36m, find the speed of projection (Take g = 9.8m/s2)

Détails de la réponse

For maximum range (Rmax)

Rmax = U2 ÷ α g where Rmax = 36m, U2 = ?, g = 9.8m/s2

36 = U2 ÷ 2 × 8.8

U2 = 36 × 2 × 9.8m = 705.8

√U = √ 705.6 = 26.5 (squaring both side)

u= 26.5m/s, U = 27m/s (Approx.)

The speed of projection = 27m/s2

If the volume of a gas is recoded as 76cm3 at a temperature of 27°C with a pressure of 800mmHg. What will be the volume of the gas at S.T.P?

Détails de la réponse

General formular of Gas laws

(P1V1) ÷ T1= (P2V2) ÷ T2

P1 = 800mmHg, V, = 76cm3, Tr = 273 + 27 = 300k

P2 = 760mmHg, V2 = ? T2= 273 + 0 = 273 + 6 = 277k

(800 × 76) ÷ 300 = (760 × V2) ÷ 273

V2 = (300 × 76 × 273) ÷ (300 × 760) = 72.8 cm3

The volume of gas as S.T.P = 72.8 cm3

A member of the crew of a SPACESHIP experiences weightlessness in a space when they

Détails de la réponse

The correct answer is: Fall freely from the earth’s gravitational field Weightlessness is experienced by the crew member of a spaceship when they are falling freely under the influence of the earth's gravity. In space, the force of gravity is still present, but objects in orbit are constantly falling towards the Earth, which creates the sensation of weightlessness. The spaceship and crew inside are all falling towards the Earth together, but because they are also moving horizontally at a high enough speed, they never actually hit the Earth. This constant state of freefall creates the feeling of weightlessness that astronauts experience in space.

Mr. F. Abioye observed his image though a plane mirror, kept a distance way from him at 4.7m in his room at what distance is the image found from Abioye eye?

Détails de la réponse

As object and image are usually at equal distance apart from the mirror

Distance between Abioye (a) and hip image (I) = AI

i.e. AI = 4.7 + 47 = 9.4m

In an elastic collisionI. Energy is conserved

II. Energy is decreased

III. Energy is increased

IV. Linear momentum conversed

Détails de la réponse

In an inelastic collision, linear momentum is conserved and energy is decreased

Momentum and kinetic energy are conserved in elastic collision

A radioactive source emits X–rays of very short wavelength (10 -13m ) what is the frequently of these rays?

Détails de la réponse

The frequency of the X-rays emitted by the radioactive source can be calculated using the formula: frequency = speed of light / wavelength The speed of light is approximately 3 x 10^8 m/s. Substituting the given wavelength of 10^-13 m into the formula, we get: frequency = 3 x 10^8 / (10^-13) = 3 x 10^21 Hz Therefore, the frequency of the X-rays emitted by the radioactive source is 3 x 10^21 Hz. Option C, which states 3 x 10^21 Hz, is the correct answer. Option A, B, and D are incorrect because they do not match the calculated frequency.

Heat losses to the surrounding is possible through the following except

Détails de la réponse

Heat can be transferred from one object to another through three different mechanisms: conduction, convection, and radiation. Expansion, on the other hand, is not a mechanism of heat transfer. Conduction is the transfer of heat through a material or between materials in contact. For example, when you touch a hot object, heat is transferred from the object to your hand by conduction. Convection is the transfer of heat by the movement of fluids, such as air or water. This is why a fan blowing air across your skin can make you feel cooler. Radiation is the transfer of heat through electromagnetic waves, such as those emitted by the sun or a fire. This is why you can feel the warmth of a fire even if you are not in direct contact with it. Expansion, on the other hand, refers to the increase in volume of a material due to an increase in temperature. While expansion can be a result of heat transfer, it is not a mechanism of heat transfer itself. Therefore, the answer to the question is Expansion. Heat can be lost to the surrounding through conduction, convection, and radiation, but not through expansion.

Which of the following is not luminous object?

Détails de la réponse

Sun are self luminous source
Moon is a non – luminous

In which of the following device in the expansion of solid is a disadvantages?

I. Simple pendulum

II. Fire alarms

III. Thermostat

IV. Bimetallic thermometer

Détails de la réponse

Simple pendulum does not depend on thermal expansion

Five alarms, Thermostat and Bimetallic thermometer are application of thermal expansion of solid

If a mango fruit dropped at a height of 50 meters. How long does it reach the ground? (take g = 10m/s2)

Détails de la réponse

The time it takes for an object to fall from a certain height can be calculated using the equation t = sqrt(2h/g), where h is the height and g is the acceleration due to gravity. In this case, the mango was dropped from a height of 50 meters and g is given as 10m/s^2. Plugging these values into the equation, we get: t = sqrt(2 x 50/10) = sqrt(10) = 3.2 sec Therefore, the mango takes 3.2 seconds to reach the ground. So the correct option is: 3.2sec.

What is the inductance (L) of an inductor whose reactance is 1? at 50/ ? hertz (H)?

Détails de la réponse

To calculate the inductance (L) of an inductor, we need to use the formula: XL = 2πfL Where XL is the reactance of the inductor, f is the frequency in hertz, and L is the inductance in henrys. In this question, we are given that the reactance of the inductor is 1 at 50 Hz. We can substitute these values into the formula and solve for L: 1 = 2π x 50 x L L = 1 / (2π x 50) L ≈ 0.00318 henrys (rounded to five decimal places) Therefore, the correct answer is: 0.01H, which is the same as 0.00318 henrys when rounded to two decimal places.

What is the S.I unit of relative density?

Détails de la réponse

The S.I unit of relative density is "has no S.I unit." Relative density, also known as specific gravity, is the ratio of the density of a substance to the density of a reference substance, usually water. Since it is a ratio of two quantities with the same unit, it does not have a unit itself. Therefore, relative density has no S.I unit. For example, if the density of a substance is 5 g/cm^3 and the density of water is 1 g/cm^3, then the relative density of the substance is 5/1 = 5. Note that the units of both densities cancel out, leaving a dimensionless quantity. In summary, relative density is a dimensionless quantity, which means it has no S.I unit.

Electrons were discovered by

Détails de la réponse

The correct option is "J.J Thompson." J.J. Thompson, a British physicist, discovered electrons in 1897. He conducted experiments with cathode ray tubes and observed that they produced a beam of negatively charged particles, which he called electrons. Thompson's discovery of electrons paved the way for further research into atomic structure and the development of modern electronics. The other options are not correct because they did not discover electrons. James Chadwick is known for discovering the neutron, Sir Isaac Newton is famous for his contributions to the fields of physics and mathematics, but he did not discover electrons, and there is no historical figure named Charles Newton who is associated with the discovery of electrons.

A motor boy of a driver saw what seem to appear to be a pool of water a head of him, while his driver’s drives a new truck on a funny day. Which of the following explains his observation?

Détails de la réponse

The correct answer is "The sun ray from the sky were passing from a hot air (layer) to cold layer". This is because the motor boy may have seen a mirage, which is a phenomenon where light is bent by the difference in temperature between a hot air layer near the ground and a colder layer of air above it. This bending of light can cause distant objects to appear to shimmer or appear as a pool of water on a hot day. This is a common occurrence in hot, desert regions where the air temperature is much higher near the ground than at higher altitudes.