JAMB UTME - Physics - 2003

Antwortdetails

For the equilateral glass prism A = 600

$\frac{3}{2}\text{Sin}\frac{\left(\frac{Dm+60}{2}\right)}{\left(\frac{60}{2}\right)}=\frac{\left(\text{Sin}\frac{Dm+60}{2}\right)}{0.5}⟹Dm={37.2}^{\circ }$

Antwortdetails

Generally in thermal/heat conduction, if 1.2 x 106 J is the heat flow per seconds; 30KM-1 is the temperature gradient of the materials; and 400Wm-1K-1 the thermal conductivity of the material, then we have that:
heat flow per seconds per unit area = thermal conductivity x temp. gradient
i.e = 1.2 x 106Area
= 400 x 30
=> 400 x 30 x Area = 1.2 x 106
∴ Area = 1.2 x 106400 x 30
Area = 100m2 or 1.0 x 102m2

Antwortdetails

When an object is placed between two parallel plane mirrors with their reflecting surfaces facing each other, an infinite number of images of the object will be formed. Each image formed by one mirror acts as an object for the other mirror, and the process continues indefinitely, with each mirror producing a new image of the previous image. The images will be arranged in a regular pattern, with each image being smaller and dimmer than the previous one, as some light is lost with each reflection. Therefore, the correct answer is "Infinite."

Antwortdetails

When a wire is stretched, its resistance increases as its cross-sectional area decreases. Similarly, if the wire is compressed, its resistance decreases as the cross-sectional area increases. Also, the resistance of a wire is directly proportional to its length, which means that as the length of a wire increases, its resistance also increases. Here, the wire is drawn out so that its new length is two times the original length. Since the resistivity of the wire remains the same, the resistance of the wire is proportional to its new length. Therefore, the new resistance is 2 times the original resistance. Next, the cross-sectional area of the wire is halved. Since resistance is inversely proportional to the cross-sectional area of a wire, the new resistance is twice the original resistance. Combining the two effects, the new resistance is (2 x 2) times the original resistance, which is 4 times the original resistance. Therefore, the new resistance is 5Ω x 4 = 20Ω. Hence, the answer is 20Ω.

Antwortdetails

When the distance from a point source of sound is doubled, the intensity of the sound wave decreases by a factor of four. The intensity of a sound wave is inversely proportional to the square of the distance from the source. This means that as the distance from the source increases, the intensity of the sound wave decreases. Doubling the distance means the distance is squared in the denominator, resulting in the intensity decreasing by a factor of four (2^2 = 4). Therefore, the correct option is: 4.00.

Antwortdetails

In the calibration of an ammeter using Faraday's laws of electrolysis, the amount of metal deposited at the electrode is directly proportional to the amount of electric charge passed through the cell. Faraday's first law states that the amount of substance produced by the passage of current through an electrolyte is directly proportional to the quantity of electricity passed through it. We can use this law to calculate the correction to be applied to the ammeter. First, we need to calculate the quantity of electricity that passed through the cell. We can use the formula: Q = It where Q is the quantity of electricity, I is the current, and t is the time. In this case, I = 1.2 A and t = 40 minutes = 2400 seconds. Q = (1.2 A) x (2400 s) = 2880 C Next, we need to calculate the amount of copper deposited at the electrode. We can use Faraday's first law, which states that the amount of substance produced is directly proportional to the quantity of electricity passed through it. The constant of proportionality is called the electrochemical equivalent, which is the amount of substance produced by the passage of one coulomb of electricity. For copper, the electrochemical equivalent is 0.000329 g/C. The amount of copper deposited can be calculated using the formula: m = ZQ where m is the mass of copper deposited, Z is the electrochemical equivalent of copper, and Q is the quantity of electricity passed through the cell. In this case, Z = 0.000329 g/C and Q = 2880 C. m = (0.000329 g/C) x (2880 C) = 0.948 g The expected amount of copper deposited is 0.990 g, but we obtained 0.948 g. This means that there was an error in the measurement of the current. To calculate the correction to be applied to the ammeter, we can use the formula: % error = [(expected value - measured value) / expected value] x 100% % error = [(0.990 g - 0.948 g) / 0.990 g] x 100% = 4.24% The % error is positive, which means that the measured value is less than the expected value. To correct for this error, we need to increase the current by the same percentage. The ammeter reading was kept constant at 1.2 A, so we need to calculate 4.24% of 1.2 A. 0.0424 x 1.2 A = 0.051 A Therefore, the correction to be applied to the ammeter is 0.05 A (option C).

Antwortdetails

This question is related to the magnification produced by a convex lens. Magnification is the ratio of the size of the image produced by a lens to the size of the object placed in front of the lens. In this question, we are given that the object is placed 10 cm from the lens and the image is formed at a distance of 25 cm from the lens. To find the magnification produced by the lens, we can use the formula: magnification = image size / object size = image distance / object distance We are not given the size of the object, but we can still find the magnification by using the given distances. image distance = 25 cm object distance = 10 cm So, the magnification produced by the lens is: magnification = image distance / object distance = 25 cm / 10 cm = 2.5 This means that the image formed by the lens is 2.5 times larger than the object placed in front of it. Therefore, the answer is option B: 2.5.

Antwortdetails

The length of a steel railroad track changes with temperature due to thermal expansion or contraction. When the temperature increases, the length of the track will also increase. The amount of expansion depends on the coefficient of linear expansion of steel, which is given in the question as 11 x 10^-6 K^-1. To find the new length of the track on a hot and dry day, we can use the formula: ΔL = αLΔT where ΔL is the change in length, α is the coefficient of linear expansion, L is the original length, and ΔT is the change in temperature. In this case, the original length L is 20 meters, the change in temperature ΔT is (40-20) = 20 degrees Celsius, and the coefficient of linear expansion α is 11 x 10^-6 K^-1. Substituting these values into the formula, we get: ΔL = (11 x 10^-6 K^-1) x (20m) x (20°C) = 0.0044m Therefore, the new length of the track on the hot and dry day is: L' = L + ΔL = 20m + 0.0044m = 20.004m So the answer is 20.004m.

Antwortdetails

To find the relative humidity, we need to first calculate the actual vapour pressure (e) at 20°C using the table. We know that the saturation vapour pressure (e_s) at 20°C is 10 mmHg, but we need to determine the actual vapour pressure to calculate the relative humidity. From the table, we can see that the saturation vapour pressure at 20°C is 17.50 mmHg. Since the actual vapour pressure is given as 10 mmHg, we can calculate the relative humidity using the following formula: Relative humidity = (actual vapour pressure/saturation vapour pressure) × 100% Relative humidity = (10/17.50) × 100% Relative humidity = 57.1% Therefore, the relative humidity in this town at 20°C is approximately 57.1%. So, option B (57.0%) is the correct answer.

Antwortdetails

The problem involves calculating the height to which a mass will be projected after being released from a compressed spring. The solution requires the use of conservation of energy principles. When the spring is compressed, it has potential energy stored in it, given by the formula: U = (1/2)kx^2 where U is the potential energy stored in the spring, k is the force constant of the spring, and x is the compression of the spring. In this case, the spring has a force constant of 500 N/m and is compressed by a length of 0.02 m. Therefore, the potential energy stored in the spring is: U = (1/2) * 500 N/m * (0.02 m)^2 = 0.1 J When the spring is released, this potential energy is converted into kinetic energy as the mass moves upwards. The kinetic energy of the mass can be calculated using the formula: K = (1/2)mv^2 where K is the kinetic energy of the mass, m is the mass of the object, and v is its velocity. At the highest point of its trajectory, the mass will have zero velocity and maximum potential energy (due to its height). Therefore, the kinetic energy at this point will be zero. Since energy is conserved, we can equate the initial potential energy of the spring to the potential energy of the mass at the highest point of its trajectory: U = mgh where g is the acceleration due to gravity, and h is the maximum height attained by the mass. Solving for h, we get: h = U / (mg) = 0.1 J / (0.005 kg * 9.81 m/s^2) = 2.04 m Therefore, the height to which the mass is projected is approximately 2 meters.

Antwortdetails

A satellite is said to be in a parking orbit if its period is exactly equal to the period of the earth as it turns its own orbit;. which is about 24hrs

Antwortdetails

Thermal equilibrium between two objects exists when their temperatures are equal. This means that the rate of transfer of thermal energy (heat) between the two objects is equal in both directions and there is no net transfer of heat from one object to the other. When two objects are in thermal contact, heat energy will always flow from the object with higher temperature to the object with lower temperature. This will continue until the temperatures of both objects become equal. At this point, thermal equilibrium is established, and there is no net flow of heat energy between the objects. Therefore, the correct option is "the temperature of both objects are equal".

Antwortdetails

Since the lever is a uniform one, its center of gravity will be acting half way (i.e 45cm)
∴from the principle of moments,
F x 45 = 30 x 30
∴ F = (30 x 30) / 45 = 20N

Antwortdetails

The stopping potential is the potential required to stop the most energetic photo-emitted electron. From the relation e Vs = K.E,(max) where e is the electron charge, and Vs is the stopping potential => e x Vs = 0.34eV
∴ Vs = (0.34eV) / e = 0.34V
∴ stopping potential = 0.34V

Antwortdetails

The uncertainty in the momentum of a particle can be calculated using Heisenberg's uncertainty principle, which states that the product of the uncertainty in the position and the uncertainty in the momentum of a particle is greater than or equal to a constant value (h/4π), where h is Planck's constant. Therefore, the uncertainty in the momentum of the particle is given by: Δp ≥ h/4πΔx Where Δx is the uncertainty in the position of the particle. Substituting the given values, we get: Δp ≥ (6.626 x 10^-34 J s) / (4π x 5.0 x 10^-10 m) Δp ≥ 1.32 x 10^-24 Ns Therefore, the uncertainty in the momentum of the particle is 1.32 x 10^-24 Ns. Hence, the correct option is: - 1.32 x 10^-24 Ns

Antwortdetails

When a charged particle moves in a magnetic field, it experiences a force called the magnetic force. This force is perpendicular to both the velocity of the particle and the magnetic field. The magnitude of the magnetic force is given by the equation F = qvBsinθ, where q is the charge of the particle, v is its velocity, B is the magnetic field, and θ is the angle between v and B. The maximum force is obtained when the angle θ is 90 degrees, because sin(90) = 1, so the force is given by F_max = qvB. According to the question, the force on the charge when θ is some other angle is half of the maximum force. So, we can write: F = (1/2) F_max F = (1/2) qvB We can rearrange this equation to find the angle θ: F = qvBsinθ = (1/2) qvB sinθ = (1/2) The only angle for which sinθ = (1/2) is 30 degrees. Therefore, the correct option is "30o".

Antwortdetails

The question gives us information about a hose of cross-sectional area and the velocity of water discharge into a container. We can use the formula: Volume = Area x Velocity x Time Area = 0.5m² (given) Velocity = 60ms⁻¹ (given) Time = 20s (given) Volume = 0.5 x 60 x 20 Volume = 600m³ Therefore, the volume of the container is 600m³. So, the correct option is: - 600m³

Antwortdetails

When an electron transitions from a higher energy level to a lower energy level, it emits energy in the form of electromagnetic radiation, such as light. The frequency of the emitted radiation is related to the energy difference between the two energy levels by the equation: ΔE = hf where ΔE is the energy difference between the two energy levels, h is Planck's constant, and f is the frequency of the emitted radiation. In this problem, the electron is transitioning from energy level E_k to the ground state E₀. The energy difference between these two levels is given by: ΔE = E_k - E₀ We are given the frequency of the emitted radiation as 8.0 x 10¹⁴ Hz. We can use the above equation to calculate the energy difference ΔE: ΔE = hf = (6.626 x 10^-34 J s) x (8.0 x 10^14 Hz) = 5.301 x 10^-19 J The energy emitted is the same as the energy difference ΔE between the two energy levels. Therefore, the energy emitted is 5.28 x 10^-19 J, which is closest to.

Antwortdetails

The pressure exerted by the stylus on the groove can be computed using the formula: pressure = force / area where force is the force exerted by the stylus on the groove, and area is the contact area between the stylus and the groove. We are given that the force exerted by the stylus is 7.7 x 10^-2 N, and the radius of the groove is 10^-5 m. The contact area between the stylus and the groove is the area of a circle with radius 10^-5 m, which is given by: area = πr^2 = π(10^-5)^2 = 3.14 x 10^-10 m^2 Substituting the values into the formula, we get: pressure = 7.7 x 10^-2 N / 3.14 x 10^-10 m^2 = 2.45 x 10^8 N/m^2 Therefore, the pressure exerted by the stylus on the groove is 2.45 x 10^8 N/m^2. The correct option is "2.45 x 10^8 N/m^2."

Antwortdetails

The velocity with which the football moves can be found using the formula: v = (F*t) / m where F is the force applied, t is the time for which the force is applied, and m is the mass of the football. Substituting the given values, we get: v = (100 * 0.8) / 0.8 = 100 m/s Therefore, the velocity with which the ball moves is 100 m/s. Note that the answer is not one of the given options. The correct answer is 100 m/s, which is a very high velocity for a football and is unlikely to be achieved in practice.

Antwortdetails

Antwortdetails

Antwortdetails

When white light is passed through a prism, it gets dispersed and is split into its constituent colors, creating a spectrum. The colors are arranged in a specific order, with red having the longest wavelength and violet having the shortest wavelength. The amount of separation between any two colors in the spectrum depends on the difference in their wavelengths. So, the pair of light rays that show the widest separation in the spectrum of white light would be those that have the largest difference in their wavelengths. Looking at the options given, we can see that the pair with the largest difference in wavelengths is blue and red, as blue has a shorter wavelength than green, while red has a longer wavelength than orange. Therefore, the answer is blue and red.

Antwortdetails

The major difference between a pure semiconductor and a pure metal is that the resistance of metals increases with temperature, while for semiconductors, it is the reverse. In other words, as the temperature of a metal increases, its resistance also increases, while for semiconductors, the resistance decreases with increasing temperature. This property is what makes semiconductors useful in electronic devices like transistors, diodes, and solar cells, where the electrical conductivity can be controlled by varying the temperature or by doping with impurities.

Antwortdetails

When an object moves in a circle, it is constantly changing its direction. This means it is constantly accelerating, even if its speed is constant. This acceleration is directed towards the center of the circle and is called the centripetal acceleration. The centripetal force, which is the force required to keep an object moving in a circle, is also directed towards the center of the circle. When the string holding the stone is suddenly cut, the centripetal force that was keeping it in circular motion is removed. The stone will now continue in a straight line in accordance with Newton's first law of motion, which states that an object in motion will remain in motion in a straight line at a constant speed, unless acted upon by an external force. Since the stone is no longer being acted upon by the centripetal force, it will fly off in a direction that is tangent to the circular path. Therefore, the correct option is "tangential to the circular path".

Antwortdetails

The phenomenon where water droplets in the atmosphere combine with dust particles in the air to reduce visibility is called "fog." Fog is a type of atmospheric moisture that occurs when the air temperature cools and becomes saturated, causing water droplets to form in the air. The combination of these droplets with dust and other particulate matter can further reduce visibility, leading to hazardous driving and flying conditions.

Antwortdetails

When an object just begins to slide on a surface inclined at an angle of 30 degrees to the horizontal, the coefficient of friction can be determined using trigonometry. The coefficient of friction is defined as the ratio of the force required to start sliding the object to the normal force (the force perpendicular to the surface). In this case, the force required to start sliding the object is equal to the product of the normal force and the coefficient of friction multiplied by the sine of the angle of inclination. The normal force is equal to the weight of the object multiplied by the cosine of the angle of inclination. Solving this equation with the given angle of inclination and assuming that the object is not accelerating, we get the coefficient of friction to be 1/√3. Therefore, the correct answer is 1/√3.

Antwortdetails

From the image provided, we can see that the zero error on the vernier calliper is 0.03 cm. The main scale reading that aligns with the zero mark on the vernier scale is 1.6 cm, and the vernier scale has an additional 0.04 cm of length that aligns with a main scale marking. Adding the main scale reading to the vernier scale reading (1.6 cm + 0.04 cm), we get a total length of 1.64 cm. Therefore, the length of the glass block is 1.64 cm.

Antwortdetails

Radioactive decay is a process in which the unstable nucleus of a radioactive atom breaks down into a more stable nucleus and emits radiation in the form of particles or waves. The rate at which a radioactive substance decays is measured in terms of its half-life, which is the time taken for half of the original sample to decay. In this problem, the count rate of a radioactive material is 800 count/min and its half-life is 4 days. This means that in 4 days, the count rate will be halved to 400 count/min, and in another 4 days, it will be halved again to 200 count/min, and so on. Therefore, if we want to know what the count rate will be in 16 days later, we need to find out how many half-lives have occurred in that time. Since the half-life of the material is 4 days, there are 4 half-lives in 16 days. This means that the count rate will be halved 4 times, which is equivalent to dividing the initial count rate (800 count/min) by 2 four times. So, the count rate in 16 days later would be: 800 count/min ÷ 2 ÷ 2 ÷ 2 ÷ 2 = 50 count/min Therefore, the answer is 50 count / min.

Antwortdetails

The depth to which the test tube sinks in water depends on the buoyant force acting on it, which in turn depends on the weight of water displaced by the test tube. The weight of water displaced is equal to the weight of the test tube, so we can use the density of water and the weight of the test tube to find the volume of water displaced. The formula for the buoyant force is given by: Buoyant force = (density of fluid) x (volume of fluid displaced) x (acceleration due to gravity) The weight of the test tube is given by: Weight of test tube = (mass of test tube) x (acceleration due to gravity) Since the test tube is placed upright, the height to which it sinks is the same as the depth of water displaced. Therefore, the depth to which the test tube sinks in water is given by: Depth = (Weight of test tube) / (Buoyant force) Substituting the values given in the question and simplifying, we get: Depth = (Weight of test tube) / ((density of water) x (volume of water displaced) x (acceleration due to gravity)) Depth = (0.0088 kg x 9.8 m/s^2) / ((1000 kg/m^3) x (pi x (0.01 m)^2 x d) x (9.8 m/s^2)) where 'd' is the depth to which the test tube sinks in meters. Solving for 'd', we get: d = 0.0282 m or 2.82 cm Therefore, the depth to which the test tube sinks in water is approximately 2.8 cm. So, the correct option is: 2.8cm.

Antwortdetails

When a ray of light passes through a glass prism, it bends or refracts. The amount of bending depends on the angle at which the light enters the prism. The angle of deviation is the angle between the incident ray and the emergent ray, measured from the direction of the incident ray. For a given prism and wavelength of light, there is a specific angle of incidence that produces the minimum angle of deviation. This angle of incidence is the angle at which the incident ray passes through the prism symmetrically, meaning it enters and exits the prism at the same angle. Therefore, the statement that is true is "the incident angle is equal to the angle of emergence". This is because when the angle of incidence equals the angle of emergence, the angle of deviation is minimized, resulting in the minimum amount of bending of the light.

Antwortdetails

The phenomenon described in the question is due to surface tension. Surface tension is a property of the surface of a liquid that causes it to behave as if it were a thin, elastic film. The molecules at the surface of a liquid experience a net inward force due to the cohesive forces between them, which causes the surface to contract and form a shape with the least surface area. In the case of an open umbrella made of silk material, the surface tension of water prevents it from passing through the small gaps between the threads of the silk. However, when the inside of the umbrella is touched, the surface tension is broken at that point, allowing the water to flow through. Capillarity is the tendency of a liquid to rise in a narrow tube due to the adhesive forces between the liquid and the tube. Osmotic pressure is the pressure that must be applied to a solution to prevent the inward flow of water across a semipermeable membrane. Viscosity is the resistance of a liquid to flow. None of these properties are relevant to the phenomenon described in the question.

Antwortdetails

An a.c current is usually expressed as I = Io sin wt; and comparing this with the given current I = 10sin (120π)t, => Io = 10.
and power in an a.c circuit is given as:
P = I2R
= (102 x 12)
= 1200W

Antwortdetails

When another resistor, R2, is connected in parallel to R1, the total resistance of the circuit decreases. As a result, the current I in the circuit will increase because the current flowing through each resistor is inversely proportional to the resistance. Therefore, option C is correct: "It will increase because the effective resistance will decrease."

Antwortdetails

The energy that can be obtained from a nuclear fission reaction is given by Einstein's famous equation: E = mc^2, where E is the energy released, m is the decrease in mass, and c is the speed of light. In this question, the decrease in mass is 0.01% of the initial mass. To calculate the decrease in mass, we need to convert the percentage to a decimal: 0.01% = 0.0001. Therefore, the decrease in mass is: 0.0001 x 0.1g = 0.00001g Now we can use Einstein's equation to calculate the energy released: E = (0.00001g) x (299792458 m/s)^2 E = 898755178.736 J This is the total energy that can be obtained from the fission of 0.1g of the material. However, the question asks for the amount of energy that could be obtained from this amount of material, so we need to divide the total energy by the mass: E = 898755178.736 J / 0.1g E = 8.98755178736 x 10^9 J/g Therefore, the answer is 9.0 x 10^9 J.

Antwortdetails

Antwortdetails

Optical fibers are thin, transparent fibers made of high-quality glass or plastic that transmit light signals over long distances by the principle of total internal reflection. When light travels through the fiber, it reflects off the walls of the fiber due to the phenomenon of refraction, which allows the light to propagate over long distances without much attenuation. Hence, the operation of an optical fiber is based on the principle of refraction of light.

Antwortdetails

This phenomenon is called nuclear binding energy. When protons and neutrons come together to form a nucleus, some of the mass is converted into energy, which is released in the process. This released energy is known as the binding energy of the nucleus. The energy equivalent of the mass difference is given by Einstein's famous equation E=mc², where E is energy, m is mass, and c is the speed of light. Therefore, the mass difference is equal to the binding energy divided by the speed of light squared.

Antwortdetails

A magnetic field is said to exist at a point if a force is exerted on a moving charge at the point. A magnetic field is created by a magnet or by the movement of electric charges, such as in a current-carrying wire. When a charged particle moves through a magnetic field, it experiences a force perpendicular to both the direction of motion and the direction of the magnetic field. This force is what causes the particle to change its direction of motion, and is what we refer to as a magnetic force. So, the correct option is "exerted on a moving charge at the point".

Antwortdetails

Iron (spft iron) is usually preferred to steel in the making of electromagnets because it is more easily magnetized and equally more easily demagnetized than [II and III]

Antwortdetails

In general, if a charged particle is accelerated between two metal plates/a region by potential difference V volts, the work done on the charge, given by the product of the charge and the potential difference, is equal to the kinetic energy of the charge
Thus eV = K.E
1.6 x 10-19 x V = 4.8 x 10-17

Antwortdetails

The induced voltage = time rate of change of magnetic flux

Antwortdetails

In vibration in a closed pipe/tube, the first resonance occurs at a position L = V/4f,
when reading from the top of the tube,

Antwortdetails

Electric bells require a cell that can deliver a high current for a short interval of time. The Leclanche cell is most suitable for this purpose. It has a simple and reliable construction, with a low internal resistance that allows it to deliver a high current for a short duration. The Daniel cell and nickel-iron accumulator have a higher internal resistance, making them unsuitable for short interval switches. The lead-acid accumulator is a rechargeable battery, and its large size and high cost make it unsuitable for use in small devices like electric bells. Therefore, the most suitable cell for short interval switches in electric bells is the Leclanche cell.

Antwortdetails

The speed of sound in a solid bar depends on the Young's modulus and density of the material. The formula for the speed of sound in a solid bar is: v = √(Y/ρ) where v is the speed of sound, Y is the Young's modulus, and ρ is the density. Substituting the given values for Young's modulus and density of aluminium, we get: v = √(7.0 x 10^10 Nm^-2 / 2.7 x 10^3 kgm^-3) Simplifying the expression inside the square root, we get: v = √(2.6 x 10^7 m^2s^-2) Taking the square root, we get: v = 5100 ms^-1 Therefore, the speed of sound produced if a solid bar of aluminium is struck at one end with a hammer is 5100 ms^-1. The correct option is (A) 5.1 x 10^3 ms^-1.

Antwortdetails

From the above diagram, if each of the resistors can dissipate a maximum of 18W, the from the relation power, P = I2R, the current in the 2Ω series resistor is given by:
I2 = P/R = 18/2 = 9 => I = √9 = 3A
The effective parallel arrangement of the two 2Ω resistors: 1/R = 1/2 + 1/2 = 1Ω
∴ Total resistance in the circuit = 1 + 2 = 3Ω
current flowing the circuit = 3A
∴ Maxi. power = P = I2R = 32 x 3 = 27W

Antwortdetails

2000W heater → 2000J/S
=> Heat supplied by the heater within 10 min
(600 seconds) = 2000 x 600
= 1200000J
∴ Heat capacity MC = 1200000/30
= 4000J/C
Heat capacity = 4.0 x 104J/C

Antwortdetails

To obtain an image at infinity in front of a concave mirror, the object must be placed at the focal point. Therefore, the correct option is "at the principal focus." When an object is placed at the focal point of a concave mirror, the light rays coming from the object are reflected parallel to the principal axis. As a result, the reflected rays never converge to a point, and the image appears at infinity. Placing the object at any other position will result in a real, inverted image formed at a specific distance from the mirror, and not at infinity. Therefore, to obtain an image at infinity in front of a concave mirror, the object must be placed at the principal focus.

Antwortdetails

When an open pipe is closed at one end, it produces the first fundamental note. The frequency of this note depends on the length of the pipe and the velocity of sound in air. The wavelength of the fundamental note must be four times the length of the pipe. The velocity of sound in air is given as P. Therefore, the frequency of the note is: f = P/4t where t is the length of the pipe. So, the correct option is: v/4t