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Pregunta 1 Informe
Which of the following materials is a good insulator?
Detalles de la respuesta
A good insulator is a material that does not easily allow heat or electricity to pass through it. It acts as a barrier, preventing the flow of heat or electricity. Out of the given options, rubber is a good insulator.
Rubber is made up of long chains of molecules that are closely packed together. These chains do not allow the easy movement of heat or electricity. This means that when heat or electricity tries to pass through rubber, it encounters resistance, making it difficult for it to flow.
In contrast, materials like silver, water, and copper are good conductors rather than insulators.
Silver is an excellent conductor of electricity and heat because its atoms have loosely bound electrons that are free to move. This allows for the easy transfer of heat or electricity throughout the material.
Water is also a good conductor of both heat and electricity. It contains charged particles called ions that can carry electric current. Additionally, water molecules are able to transfer heat through convection.
Copper is widely used in electrical wiring because it is an excellent conductor of electricity. Like silver, its atoms have free electrons that can move easily and transfer electrical energy.
Therefore, rubber is the material that serves as a good insulator, while silver, water, and copper are good conductors of heat and electricity.
Pregunta 2 Informe
The near point of a patient's eye is 50.0 cm. What power (in diopters) must a corrective lens have to enable the eye to see clearly an object 25.0 cm away?
Pregunta 3 Informe
The pinhole camera works on
Detalles de la respuesta
The pinhole camera works on the principle of the rectilinear propagation of light. This principle states that light travels in straight lines. When light passes through the tiny hole in a pinhole camera, it forms an inverted image on the opposite side of the camera. The size of the image depends on the distance between the object and the pinhole.
Pregunta 4 Informe
A wire of radius 0.2 mm is extended by 0.5% of its length when supported by a load of 1.5 kg. Determine the Young's modulus for the material of the wire.
[Take g = 10 ms-2]
Pregunta 5 Informe
The terminals of a battery of emf 24.0 V and internal resistance of 1.0 Ω is connected to an external resistor 5.0 Ω. Find the terminal p.d.
Detalles de la respuesta
To find the terminal p.d. (potential difference), we need to consider the concept of voltage in a circuit. Voltage is the amount of electrical energy per unit charge provided by a power source, in this case, the battery.
In this problem, we are given:
EMF (electromotive force) of the battery = 24.0 V
Internal resistance of the battery = 1.0 Ω
External resistor = 5.0 Ω
When the battery is connected to the external resistor, a current will flow in the circuit. This current is determined by Ohm's law, which states that the current flowing in a circuit is directly proportional to the voltage applied and inversely proportional to the resistance:
I = V / R
where:
I is the current flowing in the circuit
V is the voltage applied
R is the resistance of the circuit
In this case, the voltage applied is the emf of the battery, and the resistance is the sum of the internal resistance and the external resistor.
We can calculate the current flowing in the circuit:
I = 24.0V / (1.0Ω + 5.0Ω) = 24.0V / 6.0Ω = 4.0A
Now, the terminal p.d. is the voltage drop across the external resistor. We can calculate it using Ohm's law:
V = I * R
Substituting the values:
V = 4.0A * 5.0Ω = 20.0V
Therefore, the terminal p.d. is 20.0V.
Pregunta 6 Informe
The sensitivity of a thermometer is
Detalles de la respuesta
The sensitivity of a thermometer refers to the smallest temperature change that it can detect or measure. In other words, it measures how fine or precise the thermometer is in detecting changes in temperature. A thermometer with high sensitivity is able to detect even small changes in temperature, while a thermometer with low sensitivity may only detect larger temperature fluctuations.
Therefore, in the given options, the statement "the smallest temperature change that can be detected or measured" accurately describes the sensitivity of a thermometer.
Pregunta 7 Informe
Which of the following is a type of wave that is both mechanical and longitudinal?
Detalles de la respuesta
A wave that is both mechanical and longitudinal is sound waves.
Sound waves are created by the vibration of an object, such as a speaker, which causes the air particles around it to vibrate. These vibrations then travel through the air in the form of a wave.
Sound waves are classified as mechanical waves because they require a medium, such as air, water, or solid objects, to travel through. Without a medium, sound waves cannot propagate.
Furthermore, sound waves are classified as longitudinal waves because the particles in the medium vibrate parallel to the direction of the wave. This means that as the sound wave travels, the particles in the medium move back and forth in the same direction as the wave itself.
In contrast, water waves and seismic waves are mechanical waves, but they are not longitudinal. Water waves are categorized as transverse waves because the particles in the water move up and down at right angles to the direction of the wave. Seismic waves, which include earthquake waves, can be both transverse and longitudinal, but typically the primary seismic waves are classified as transverse waves.
Lastly, light waves are not mechanical waves but rather electromagnetic waves. They do not require a medium to travel through and can propagate in a vacuum, unlike sound waves.
Pregunta 8 Informe
A 400 N box is being pushed across a level floor at a constant speed by a force P of 100 N at an angle of 30.0° to the horizontal, as shown in the the diagram below. What is the coefficient of kinetic friction between the box and the floor?
Detalles de la respuesta
W = 400 N; P = 100 N; θ = 30o; μ = ?
Frictional force (Fr) = μR (where R is the normal reaction)
The forces acting along the horizontal direction are Fr and Px
∴ Pcos 30° - Fr = ma (Pcos 30° is acting in the +ve x-axis while Fr in the -ve x-axis)
⇒ 100cos 30° - μR = ma
Since the box is moving at constant speed, its acceleration is zero
⇒ 100cos 30° - μR = 0
⇒ 100cos 30o = μR ----- (i)
The forces acting in the vertical direction are W, Py and R
∴ R - Psin 30° - W = 0 (R is acting upward (+ve) while Py and W are acting downward (-ve) and they are at equilibrium)
⇒ R - 100sin 30° - 400 = 0
⇒ R = 100sin 30° + 400
⇒ R = 50 + 400 = 450 N
From equation (i)
⇒ 100cos 30° = 450μ
⇒μ=100cos30°
N = 100cos30°450
= μ = 0.19
Pregunta 9 Informe
A lorry accelerates uniformly in a straight line with acceleration of 4ms-1 and covers a distance of 250 m in a time interval of 10 s. How far will it travel in the next 10 s?
Detalles de la respuesta
Pregunta 10 Informe
A charge of 4.6×10−5
C is placed in an electric field of intensity 3.2×104
Vm−1
. What is the force acting on the electron?
Detalles de la respuesta
To calculate the force acting on the charge in an electric field, we can use the formula: F = q * E Where: F is the force acting on the charge, q is the charge of the particle, and E is the electric field intensity. In this case, the charge is given as 4.6 × 10^(-5) C and the electric field intensity is given as 3.2 × 10^4 V/m. Substituting these values into the formula: F = (4.6 × 10^(-5) C) * (3.2 × 10^4 V/m) To multiply numbers in scientific notation, we multiply the coefficients and add the exponents: F = (4.6 * 3.2) * (10^(-5 + 4)) C * V/m F = 14.72 * 10^(-1) C * V/m To simplify, we can convert the result to standard form: F = 1.472 C * V/m Therefore, the force acting on the charge is **1.472 N**.
Pregunta 11 Informe
Which of the following is NOT a limitation of experimental measurements?
Detalles de la respuesta
Instrument resolution is not a limitation of experimental measurements. It is the smallest change in a measured quantity that can be detected by an instrument. While instrument resolution limits the accuracy of a measurement, it is not a limitation of experimental measurements itself.
Pregunta 12 Informe
Find the tension in the two cords shown in the figure above. Neglect the mass of the cords, and assume that the angle is 38° and the mass m is 220 kg
[Take g = 9.8 ms-2]
Detalles de la respuesta
W = mg = 220 x 9.8 = 2156 N
⇒Sin 38º = 2156T1
⇒ T1 = 2156Sin38
⇒ T1 = 3502 N
Cos 38º = T2T1
⇒ T2 = 3502 x Cos 38º
⇒ T2 = 2760 N
; T1
= 3502 N, T2
= 2760 N.
Pregunta 13 Informe
The pitch of a musical note is determined by the frequency of the sound wave that it produces. If two instruments have the same frequency, which of the following factors will most affect the difference in their pitches?
Detalles de la respuesta
The frequency of a sound wave is proportional to the tension of the string. If two instruments have the same frequency, but one has a tighter string, then the instrument with the tighter string will have a higher pitch.
The other factors listed, such as the size of the instrument, the material of the instrument, and the shape of the instrument, will also affect the pitch of the instrument, but they will have a smaller effect than the tension of the string.
Pregunta 14 Informe
A piano wire 50 cm long has a total mass of 10 g and its stretched with a tension of 800 N. Find the frequency of the wire when it sounds its third overtone note.
Detalles de la respuesta
T=800N; I=50cm=0.5m,
m=10g=0.01kg
fundamental freq: fo
=?
fo
= 121√Tμ
μ =m1
=0.010.5
⇒ fo
=12×0.5
√8000.02
fo
⇒√ 40,000
⇒1st overtone = 2fo
=2×200 = 400Hz
⇒2nd overtone =3fo
=3×200=600Hz
∴3rd over tone= 4fo
=4×200=800Hz
Pregunta 15 Informe
How much net work is required to accelerate a 1200 kg car from 10 ms-1 to 15 ms-1
Detalles de la respuesta
Pregunta 16 Informe
Which of the following is an example of a couple?
Detalles de la respuesta
A couple is a pair of forces that are equal in magnitude but opposite in direction, and that are applied to a body at different points. The forces of a couple do not produce any translation, but they do produce a rotation.
Pregunta 17 Informe
The property of wave shown in the diagram above is?
Detalles de la respuesta
The property of the wave shown in the diagram is diffraction.
Diffraction is the bending or spreading out of waves as they encounter an obstacle or pass through an opening. It occurs when waves encounter an obstacle that is comparable in size to their wavelength.
In the diagram, you can see that the wave is encountering an opening or a slit, and as a result, it is spreading out or bending around the edges of the opening. This bending or spreading out is characteristic of diffraction.
Diffraction is an important phenomenon in wave behavior and is observed in various situations, such as when sound waves pass through a doorway or when light waves pass through a narrow slit. It helps us understand how waves interact with obstacles and openings in their path.
In summary, the property of the wave shown in the diagram is diffraction, which is the bending or spreading out of waves as they encounter an obstacle or pass through an opening.
Pregunta 18 Informe
The diagram above illustrates the penetrating power of some types of radiation. X, Y and Z are likely
Detalles de la respuesta
The penetrating power of alpha rays, beta rays, and gamma rays varies greatly. Alpha particles can be blocked by a few pieces of paper. Beta particles pass through paper but are stopped by aluminum foil. Gamma rays are the most difficult to stop and require concrete, lead, or other heavy shielding to block them.
Therefore, X = γ-ray; Y = α-particle; Z = β-particle
Pregunta 19 Informe
Which of the following is a type of incandescent light source?
Detalles de la respuesta
The Tungsten filament lamp is a type of incandescent light source.
An incandescent light source works by using electricity to heat a filament inside the bulb until it becomes so hot that it emits light. In a tungsten filament lamp, the filament is made of tungsten, which is a metal that has a very high melting point. This allows the filament to get extremely hot without melting.
When an electric current passes through the filament, it heats up and starts to glow, producing visible light. The light emitted by a tungsten filament lamp is actually a result of the high temperature, which causes the atoms in the filament to vibrate and release energy in the form of light.
Incandescent light sources like tungsten filament lamps have been widely used for many years because they produce a warm, yellowish light that is similar to natural sunlight. However, they are not very energy-efficient, as a significant amount of the electrical energy is converted into heat rather than light.
In recent years, there has been a shift towards more energy-efficient alternatives like LED lamps and fluorescent lamps. LED lamps use a different mechanism to produce light, using a semiconductor that emits light when electric current passes through it. Fluorescent lamps use a gas-filled tube that emits ultraviolet light when electric current flows through it, and this ultraviolet light is then converted into visible light by a phosphor coating inside the tube.
So, in summary, the tungsten filament lamp is the type of incandescent light source among the options given. It works by heating a tungsten filament to a very high temperature, causing it to emit light. However, it is less energy-efficient compared to LED and fluorescent lamps.
Pregunta 20 Informe
On a particular hot day, the temperature is 40°C and the partial pressure of water vapor in the air is 38.8 mmHg. What is the relative humidity?
Detalles de la respuesta
To calculate the relative humidity, we need to understand the concept of saturation and how much water vapor the air can hold at a given temperature.
Saturation is the point at which the air is holding the maximum amount of water vapor it can hold at a particular temperature. Once the air reaches saturation, any additional moisture will start to condense into liquid water.
The amount of water vapor that the air can hold increases with temperature. Warmer air can hold more water vapor, while cooler air can hold less.
Now, let's calculate the relative humidity using the given information:
1. Find the saturation vapor pressure at 40°C: - The saturation vapor pressure is the maximum amount of water vapor the air can hold at a specific temperature. - At 40°C, the saturation vapor pressure is approximately 55.3 mmHg.
2. Calculate the relative humidity: - Relative humidity is the ratio of the current partial pressure of water vapor to the saturation vapor pressure, expressed as a percentage. - Relative Humidity = (Partial pressure of water vapor / Saturation vapor pressure) * 100 - In this case, the partial pressure of water vapor is 38.8 mmHg and the saturation vapor pressure at 40°C is 55.3 mmHg. - Plugging in these values into the formula, we get: Relative Humidity = (38.8 mmHg / 55.3 mmHg) * 100 = 70.2%
Therefore, the relative humidity on this particular hot day is approximately 70%.
Answer: The correct option is 70.
Pregunta 21 Informe
What is the amount of heat required to raise the temperature of a 0.02 kg of ice cube from −10oC to 10oC ?
[specific latent heat of fusion of ice = 3.34 x 105 Jkg−1, Specific heat capacity of water = 4200 Jkg−1 k−1
Specific heat capacity of ice = 2100 Jkg−1k−1
Pregunta 22 Informe
In the diagram above, if the south poles of two magnets stroke a steel bar, the polarities at X and Y will respectively be
Detalles de la respuesta
The polarities at X and Y would be north and north.
Pregunta 23 Informe
Which of the following statements regarding the application of electrical conduction via gases is/are correct?
Electrical conduction in gas is applied in:
(i) The identification of gases
(ii) Lighting/fluorescent tubes
(iii) Photocells
(iv) Cathode ray oscilloscope/T.V. tubes
Detalles de la respuesta
Electrical conduction of gas is applied in:
(i) The identification of gases
(ii) Lighting/fluorescent tubes
(iii) Advertising industry/Neon signs
(iv) Cathode ray oscilloscope/T.V. tubes
Pregunta 24 Informe
Name the type of equilibrium for each position of the ball
Detalles de la respuesta
To determine the type of equilibrium for each position of the ball, we need to understand what each type of equilibrium means. 1. **Unstable equilibrium**: This occurs when a small disturbance or change in the system causes the object to move away from its equilibrium position. In other words, the system is "unstable" and will not return to its original position on its own. 2. **Neutral equilibrium**: This occurs when a small disturbance or change in the system does not cause the object to move away from its equilibrium position. The system remains in its new position without any tendency to return to its original position. 3. **Stable equilibrium**: This occurs when a small disturbance or change in the system causes the object to move away from its equilibrium position, but the system has a tendency to return to its original position on its own. Now, let's analyze each position of the ball: A - **Unstable equilibrium**: Suppose the ball is placed at position A. If the ball is slightly disturbed or moved from this position, it will roll away further from its original position and won't come back on its own. Hence, position A is an unstable equilibrium. B - **Stable equilibrium**: Suppose the ball is placed at position B. If the ball is slightly disturbed or moved from this position, it will oscillate back and forth but eventually come back to its original position. This indicates that position B is a stable equilibrium. C - **Neutral equilibrium**: Suppose the ball is placed at position C. If the ball is slightly disturbed or moved from this position, it will stay at the new position without any tendency to return to its original position. This identifies position C as a neutral equilibrium. Based on the explanations above, the correct answer is: A - unstable, B - stable, C - neutral.
Pregunta 25 Informe
How much work is done against the gravitational force on a 3.0 kg object when it is carried from the ground floor to the roof of a building, a vertical climb of 240 m?
Detalles de la respuesta
To calculate the work done against gravitational force, we can use the formula:
Work = Force x Distance
In this case, the force we are working against is the gravitational force. The gravitational force is the force with which the Earth pulls objects towards its center. The formula for gravitational force is:
Force = Mass x Acceleration due to gravity
The mass of the object is given as 3.0 kg. The acceleration due to gravity on Earth is approximately 9.8 m/s^2.
Now, we need to find the distance the object is being carried, which is 240 m.
Plugging these values into the formulas, we have:
Force = 3.0 kg x 9.8 m/s^2 = 29.4 N
Work = 29.4 N x 240 m
Therefore, the work done against the gravitational force is equal to 29.4 N x 240 m = 7056 J = 7.1 kJ (rounded to one decimal place).
So, the correct answer is 7.2 kJ.
Pregunta 26 Informe
A relative density bottle has a mass of 19 g when empty. When it is completely filled with water, its mass is 66 g. What will be its mass if completely filled with alcohol of relative density 0.8?
Detalles de la respuesta
Let mb=mass of empty bottle,
mw
=mass of water only and
ma
= mass of alcohol only
given; mb
=19g
mb
+ mw
= 66g
mb
+ ma
= ?
R.d=0.8
R.d=mass of alcohol
massofalcoholmassofequalvolumeofwater
mass of equal volume of water = mw
=66-19=47g
0.8 = ma47
ma
=0.8×47 =37.6g
mb
+ ma
= 19+37.6=56.6g
Pregunta 27 Informe
A missile is launched with a speed of 75 ms-1 at an angle of 22° above the surface of a warship. Find the horizontal range achieved by the missile. Ignore the effects of air resistance.
[Take g = 10 ms-1]
Pregunta 28 Informe
A 35 kΩ is connected in series with a resistance of 40 kΩ. What resistance R must be connected in parallel with the combination so that the equivalent resistance is equal to 25 kΩ?
Detalles de la respuesta
For the combination in series;
⇒R1 = 35kΩ + 40kΩ = 75kΩ
R is combined with 75kΩ in parallel to give 25kΩ
= 1Req
= 1R
+ 1R
= 125
= 1R
+ 175
= 125
- 175
+ 1R
= 3−175
= 1R
= 275
= 1R
= 752
= R
; R = 37.5k Ω
Pregunta 29 Informe
What is the name of the model of the atom that describes electrons as orbiting the nucleus in specific energy levels?
Detalles de la respuesta
The name of the model of the atom that describes electrons as orbiting the nucleus in specific energy levels is the Bohr model.
The Bohr model was proposed by Danish physicist Niels Bohr in 1913. According to this model, electrons revolve around the nucleus in specific energy levels or shells. Each energy level corresponds to a certain amount of energy that an electron possesses. The energy levels are represented by whole numbers, with the closest energy level to the nucleus having the lowest energy and subsequent energy levels having higher energies.
Bohr's model also stated that electrons can only exist in certain fixed orbits around the nucleus. These orbits have a specific distance from the nucleus and are called stationary states. Electrons can move between these energy levels by absorbing or emitting energy in the form of photons.
The Bohr model successfully explained the observed emission and absorption spectra of atoms, as well as the stability of atoms. However, it has limitations in fully describing the behavior of electrons. It does not accurately represent the path or trajectory of electrons and does not account for other quantum effects.
Overall, the Bohr model provides a simplified and understandable framework for visualizing the arrangement of electrons in an atom, with electrons occupying specific energy levels or shells around the nucleus.
Pregunta 30 Informe
Which of the following liquids has the highest surface tension?
Detalles de la respuesta
Surface tension is a property of liquids that arises due to the cohesive forces between the molecules at the surface. It can be thought of as the "skin" or "film" that forms on the surface of a liquid.
Considering the options given:
- Water: Water molecules have strong cohesive forces, allowing them to form hydrogen bonds with each other. As a result, water has relatively high surface tension.
- Mercury: Mercury is a metal with metallic bonding, which is much stronger than the cohesive forces in liquids. As a result, mercury has very high surface tension.
- Oil: Oils typically consist of nonpolar molecules, which have weaker cohesive forces compared to polar molecules like water. Therefore, oil generally has lower surface tension than water.
Based on this information, we can conclude that mercury has the highest surface tension among these liquids.
Pregunta 31 Informe
When light of a certain frequency is incident on a metal surface, no photoelectrons are emitted. If the frequency of the light is increased, what happens to the stopping potential?
Detalles de la respuesta
When light of a certain frequency is incident on a metal surface, no photoelectrons are emitted. This is because the energy of the photons in the light is not enough to overcome the work function of the metal, which is the minimum amount of energy required to remove an electron from the metal surface.
If the frequency of the light is increased, it means that the energy of the photons increases. This increase in energy means that there is now enough energy to overcome the work function of the metal. As a result, photoelectrons are now emitted from the metal surface.
Now, let's consider the stopping potential. The stopping potential is the minimum potential difference that needs to be applied across a pair of electrodes in order to stop the flow of photoelectrons from reaching the other electrode.
When the frequency of the light is increased, the energy of the photons also increases. This means that the photoelectrons have more kinetic energy when they are emitted from the metal surface. As a result, a higher stopping potential is required to stop the more energetic photoelectrons from reaching the other electrode.
Therefore, the stopping potential increases when the frequency of the light is increased.
Pregunta 32 Informe
A man swung an object of mass 2 kg in a circular path with a rope 1.2 m long. If the object was swung at 120 rev/min, find the tension in the rope.
Detalles de la respuesta
To find the tension in the rope, we can first use the formula for centripetal force, which is given by:
F_centripetal = (m * v^2) / r
where: - F_centripetal is the centripetal force - m is the mass of the object - v is the velocity of the object - r is the radius of the circular path
In this case, the mass of the object (m) is given as 2 kg and the radius (r) is given as 1.2 m.
Now, to find the velocity (v), we need to convert the given value of 120 rev/min to m/s.
Here's how we can do that:
1. First, convert the revolutions per minute (rev/min) to revolutions per second (rev/s) by dividing by 60 (since there are 60 seconds in a minute):
120 rev/min = 120/60 rev/s = 2 rev/s
2. Next, we need to convert the revolutions per second to the linear velocity in meters per second (m/s). To do this, we need to find the circumference of the circular path.
The circumference of a circle is given by the formula:
C = 2πr where r is the radius of the circular path.
Substituting the value of the radius (r = 1.2 m) into the formula, we have:
C = 2π * 1.2 = 2.4π Now, to find the linear velocity (v), we can multiply the circumference (C) by the number of revolutions per second (2 rev/s):
v = C * rev/s = 2.4π * 2 = 4.8π m/s
Now that we have the values of m (2 kg) and v (4.8π m/s), we can substitute them into the centripetal force formula to find the tension in the rope:
F_centripetal = (m * v^2) / r = (2 * (4.8π)^2) / 1.2
Simplifying further:
F_centripetal = (2 * 23.04π^2) / 1.2
F_centripetal = 38.4π^2
Finally, to get a numerical value for the tension in the rope, we can approximate the value of π to 3.14 and calculate the centripetal force:
F_centripetal ≈ 38.4 * 3.14^2 ≈ 379 N
Therefore, the tension in the rope is approximately 379 N.
Therefore, the correct answer is 379.
Pregunta 33 Informe
Which of the following thermometers measures temperature from the thermal radiation emitted by objects?
Detalles de la respuesta
A pyrometer thermometer measures temperature from the thermal radiation emitted by objects.
When objects are heated, they emit thermal radiation, which is a form of electromagnetic radiation. This radiation is primarily in the infrared wavelength range. A pyrometer thermometer is specifically designed to measure the intensity of this thermal radiation and convert it into a temperature reading.
The pyrometer thermometer works based on the principle of measuring the amount of thermal radiation reaching the sensor. This is done using a detector that is sensitive to the infrared wavelength range. The detector absorbs the thermal radiation emitted by the object and generates an electrical signal proportional to the intensity of the radiation.
The electrical signal from the detector is then processed by the thermometer's electronics to calculate and display the corresponding temperature. The calibration of the thermometer ensures accurate temperature readings based on the known relationship between the intensity of thermal radiation and temperature.
Pyrometer thermometers are commonly used in industrial applications where contact-based temperature measurement methods are not feasible or accurate enough. They can measure temperatures of objects from a distance without physically touching them, which makes them suitable for measuring high temperatures, moving objects, or objects in hazardous or inaccessible environments.
Therefore, the pyrometer thermometer is the correct option for measuring temperature from thermal radiation emitted by objects.
Pregunta 34 Informe
Pregunta 35 Informe
When a water droplet is placed on a freshly cut piece of wood, it spreads out to form a thin layer because the wood is
Detalles de la respuesta
When a water droplet is placed on a freshly cut piece of wood, it spreads out to form a thin layer because the wood is adhesive to water.
Adhesion is the attraction between different substances, in this case, water and wood. Wood is a porous material, meaning it has tiny holes or gaps in its surface. These tiny holes create a large surface area for the water droplet to interact with.
When the water droplet comes into contact with the wood, the adhesive forces between the water molecules and the wood molecules are stronger than the cohesive forces between the water molecules. This causes the water droplet to spread out, trying to maximize its contact with the wood surface.
The spreading out of the water droplet forms a thin layer because the wood surface is not completely smooth. Instead, it has irregularities and imperfections, which allow the water to seep into those gaps and spread out further.
Therefore, when a water droplet is placed on a freshly cut piece of wood, it spreads out to form a thin layer due to the adhesive forces between the water and the wood surface.
Pregunta 36 Informe
Which of the following is/are not true about the heat capacity of a substance?
(i) It is an intensive property
(ii) Its S.I unit is jK−1
(iii) It is an extensive property
(iv) Its S.I unit is jkg−1
Detalles de la respuesta
The correct answer is (ii) and (iii) only. The heat capacity of a substance is a measure of how much heat energy is required to raise the temperature of the substance by a certain amount. It is an important property in thermodynamics. (i) It is not true that heat capacity is an intensive property. Intensive properties do not depend on the size or amount of the substance. For example, density and temperature are intensive properties. However, heat capacity does depend on the size or amount of the substance. The heat capacity of a substance increases with its mass or amount. Therefore, statement (i) is false. (ii) It is true that the SI unit of heat capacity is joules per kelvin (J/K). Heat capacity is defined as the amount of heat energy (in joules) required to raise the temperature of a substance by 1 degree kelvin. Therefore, statement (ii) is true. (iii) It is not true that heat capacity is an extensive property. Extensive properties depend on the size or amount of the substance. Examples of extensive properties include mass and volume. However, heat capacity is an intensive property as explained earlier. Therefore, statement (iii) is false. (iv) It is true that the SI unit of heat capacity is joules per kilogram per kelvin (J/(kg·K)). This unit is commonly used for specific heat capacity, which is the heat capacity per unit mass. Therefore, statement (iv) is true. In summary, the correct statement is that (ii) and (iii) are not true about the heat capacity of a substance.
Pregunta 37 Informe
An explosion occurs at an altitude of 312 m above the ground. If the air temperature is -10.00°C, how long does it take the sound to reach the ground?
[velocity of sound at 0 deg = 331 ms-1]
Pregunta 38 Informe
A travelling wave of amplitude 0.80 m has a frequency of 16 Hz and a wave speed of 20 ms-1
Calculate the wave number of the wave.
Detalles de la respuesta
The wave number of a wave is defined as the number of wavelengths per unit distance. It represents the spatial frequency of the wave.
In this case, the wave has a frequency of 16 Hz, which means it completes 16 cycles or oscillations per second. Each cycle corresponds to one wavelength.
The wave speed is given as 20 m/s, which is the speed at which the wave propagates through the medium.
To calculate the wave number, we can use the formula:
Wave number (k) = 2? / wavelength (?)
First, we need to find the wavelength of the wave. We can use the formula:
Wave speed (v) = frequency (f) x wavelength (?)
Rewriting the formula, we have:
Wavelength (?) = wave speed (v) / frequency (f)
Substituting the given values, we have:
Wavelength (?) = 20 m/s / 16 Hz
Simplifying the expression, we get:
Wavelength (?) = 1.25 m
Now, we can calculate the wave number using the formula:
Wave number (k) = 2? / wavelength (?)
Substituting the value of the wavelength, we get:
Wave number (k) = 2? / 1.25 m
Simplifying the expression, we get:
Wave number (k) ? 5.03
Therefore, the wave number of the wave is approximately 5.
Pregunta 39 Informe
An open-tube mercury manometer is used to measure the pressure in a gas tank. When the atmospheric pressure is 101,325 Pa
, what is the absolute pressure in Pa
in the tank if the height of the mercury in the open tube is 25 cm higher
Pregunta 40 Informe
From the diagram above, if the potential difference across the resistor, capacitor and inductor are 60V, 120V and 30V respectively, the effective potential difference is
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