JAMB UTME - Physics - 2024

Detalhes da Resposta

In order to find out how much energy the accumulator takes in, given that it is 90% efficient and gives out 2700J of energy, we can use the formula for efficiency:

Efficiency = (Useful Energy Output / Total Energy Input) × 100%

Given:

Efficiency = 90%

Useful Energy Output = 2700J

We need to calculate the Total Energy Input (how much energy the accumulator takes in). Rearranging the formula to solve for Total Energy Input, we get:

Total Energy Input = Useful Energy Output / Efficiency

Substitute the known values:

Total Energy Input = 2700J / 0.9

Calculate the input:

Total Energy Input = 3000J

Therefore, the accumulator takes in 3000J of energy.

Detalhes da Resposta

A non-rechargeable cell, commonly known as a primary cell, is a type of chemical battery that is designed to be used once until the chemical reactions that produce electricity are exhausted. After this point, the cell cannot be reversed or recharged.

In the given examples, the dry leclanche cell is a well-known example of a non-rechargeable cell. It is commonly used in everyday devices like remote controls, wall clocks, and torches. This cell type utilizes zinc and manganese dioxide as electrodes and relies on a moist paste of ammonium chloride for the electrolyte.

The other examples, such as nickel iron, mercury cadmium, and lead-acid, involve rechargeable cells (secondary cells) that are specifically designed to endure multiple charges and discharges throughout their useful life. Thus, unlike the dry leclanche cell, these can be recharged after use.

Therefore, the dry leclanche cell is an ideal example of a non-rechargeable cell because it can only be used once. After depletion, it cannot be recharged or reused.

Detalhes da Resposta

The diagram is that of the virus. Viruses are obligate parasites, meaning they can't produce their own energy or proteins. They enter the host cell and use the cell's machinery to make their own nucleic acids and proteins. Viruses also use the host cell's lipids and sugar chains to create their membranes and glycoproteins. This parasitic replication can severely damage the host cell, which can lead to disease or cell death. They usually enter your body through your mucous membranes. These include your eyes, nose, mouth, penis, vagina and anus.

Viruses are a unique type of organism that are not plants, animals, or bacteria. They are often classified in their own kingdom. However, for the sake of the question, since most of their attributes and metabolic activities are more of the bacteria, we'll go with option A - Monera

Detalhes da Resposta

In voltage measurement, a **potentiometer is preferred to a voltmeter** primarily because it **consumes negligible current**. Let me explain this in simpler terms:

A **voltmeter** is an instrument used to measure the potential difference (voltage) across two points in an electrical circuit. However, when a voltmeter is connected, it draws a small amount of current from the circuit to make the measurement, which can slightly alter the voltage being measured. This is particularly an issue in high-resistance circuits where even a small current draw can significantly affect the measurement.

On the other hand, a **potentiometer** is a device designed to measure voltage by comparing it with a known reference voltage without drawing current from the circuit under test. It comes into balance at a point where no current flows through it, ensuring that the measurement is not influenced by the potentiometer itself. This makes it a non-invasive method of measuring voltage, which is particularly useful for precise measurements in sensitive circuits.

Here’s a brief explanation about why the other options listed are less relevant:

• A **wider range** is not a definitive advantage of potentiometers over voltmeters, as it depends on the settings and design of the specific instrument.
• **Bulkiness** is not a factor that inherently makes a potentiometer preferable; in fact, it can sometimes be a disadvantage due to space constraints.
• **Faster response** is not typically associated with potentiometers compared to voltmeters, as both can be designed to have quick response times depending on the technology used.

Therefore, the key advantage of the potentiometer is its **ability to measure voltage without altering the circuit**, which stems from its negligible current consumption. This **ensures more accurate and reliable measurements** in many applications.

Detalhes da Resposta

To determine the amount of current required, we need to use Faraday's laws of electrolysis. The first law states that the mass of the substance deposited at an electrode is directly proportional to the quantity of electricity (or charge) that passes through the electrolyte.

Here, we have:

• The mass of the metal deposited, \( m \), is 0.02 kg.
• The electrochemical equivalent, \( z \), is 1.3 x 10^-7 kg/C.
• The time during which the current is applied, \( t \), is 120 seconds.

According to Faraday's first law of electrolysis, the mass (\( m \)) can be calculated by the formula:

m = z \times I \times t

Where:

• m is the mass of the substance deposited (in kilograms).
• z is the electrochemical equivalent (in kg/Coulomb).
• I is the current (in amperes).
• t is the time (in seconds).

Rearranging the formula to solve for current \( I \):

I = \(\frac{m}{z \times t}\)

Substituting the given values into the formula:

I = \(\frac{0.02 \, \text{kg}}{1.3 \times 10^{-7} \, \text{kg/C} \times 120 \, \text{s}}\)

Calculating the denominator:

I = \(\frac{0.02}{1.56 \times 10^{-5}}\)

Solving for \( I \):

I = 1282.05 \, \text{A}

Thus, the appropriate amount of current required to deposit 0.02 kg of metal in 120 seconds is approximately 1.3 x 10³ A.

Detalhes da Resposta

A pinhole camera is a simple camera device that uses a tiny hole to project an inverted image of the scene in front of it onto a surface at the back of the camera. When you diminish the hole of a pinhole camera, meaning you make the hole smaller, a few effects occur on the resulting image. Here’s what happens:

• Firstly, when the pinhole is smaller, less light enters the camera. This results in the image becoming darker.
• Additionally, with a smaller hole, the path of light rays becomes narrower which helps to reduce blurring and overlaps from being out of focus. Consequently, the image becomes sharper.

Therefore, reducing the size of the pinhole in a pinhole camera results in the image becoming both darker and sharper.

Answer: II only (The image becomes sharper.)

Detalhes da Resposta

To find the value of the capacitance, we need to use the formula for capacitance:

Capacitance (C) = Charge (Q) / Voltage (V)

In this problem, the charge (Q) is given as 30 Coulombs (C) and the voltage (V) is 5 Volts (V). We can plug these values into the formula:

C = 30 C / 5 V

Calculating the above expression gives:

C = 6 Farads (F)

Therefore, the value of the capacitor is 6 Farads.

Detalhes da Resposta

In insects, the structure responsible for the exchange of gases is the tracheae. Insects have a unique respiratory system where air is taken in through tiny openings called spiracles located on the surface of their body.

The air then travels directly into a network of tubes known as the tracheae. The tracheae branch out extensively throughout the insect's body, allowing oxygen to diffuse directly to the insect's tissues and cells. The carbon dioxide produced in the cells travels back through the tracheae and exits the body through the spiracles.

Other structures like the skin, Malpighian tubules, and flame cells have different functions:

• Skin: Insects do not use their skin for gas exchange like some other animals do; their skin is generally designed to protect them from environmental elements.
• Malpighian tubules: These are involved in the excretory system of insects, helping to remove waste products from their bodies.
• Flame cells: These are structures found in certain flatworms and are part of their excretory system; they are not present in insects.

Thus, the correct answer is the tracheae as they specifically enable the exchange of gases in insects.

Detalhes da Resposta

 Measuring ionization current in air:
This is typically not a function of an electroscope. While it can detect charge, it does not measure ionization currents, which require specialized equipment like an ionization chamber.

Detalhes da Resposta

When the thermal energy in a solid is increased, the solid particles gain energy and begin to vibrate more vigorously. As the temperature rises, these particles eventually have enough energy to overcome the forces holding them in their fixed positions. This leads to a change of state from a solid to a liquid. This process is known as melting.



To further understand this, imagine an ice cube. As it absorbs heat, it gains energy, and the ice (which is a solid) starts to turn into water (which is a liquid). This transition is what we refer to as melting.



Thus, the term that describes this change of state, when a solid is heated and turns into a liquid, is melting.

Detalhes da Resposta

density of methanol =  800kgm−3 ${}^{-3}$ → 0.8gcm−3 ${}^{-3}$ 

At equilibrium, the density of methanol = the density of liquid x

ρ $\rho$ x h x g = ρ $\rho$x ${}_x$ x hx ${}_x$ x g

0.8 x 7.1 =  ρ $\rho$x ${}_x$ x  14.2

 ρ $\rho$x ${}_x$ = 0.8×7.114.2 $\frac{0.8\times 7.1}{14.2}$ = 0.4gcm−3 ${}^{-3}$ 

∴ $\therefore$, the relative density of liquid x = 0.4

Relative density of X = density of liquid xdensity of methanol $\frac{\text{density of liquid x}}{\text{density of methanol}}$ = 0.40.8 $\frac{0.4}{0.8}$ = 0.5

Detalhes da Resposta

The magnetic force on an electron in a magnetic field (F) = q v Bsinθ $\theta$

B = 10T, q =  3 x 107 ${}^7$m/, θ $\theta$ = 60º and q =  1.6 x 10−19 ${}^{-19}$C

F =  1.6 x 10−19 ${}^{-19}$ x 3 x 107 ${}^7$ x 10 x sin 60º ≊ $\approxeq$ 4.162 × 10−11 ${}^{-11}$N

Detalhes da Resposta

When we say that the displacement of a car is proportional to the square of time (d ∝ t²), it indicates a relationship between displacement (d) and time (t). This relationship is characteristic of motion where there is constant acceleration. Essentially, it means that the car is not moving at a constant speed (velocity) but is accelerating at a constant rate.

The mathematical representation of this scenario can be expressed using the formula for displacement under uniform acceleration:

d = ut + (1/2)at².

In this equation:

• d = displacement
• u = initial velocity (which could be zero)
• a = acceleration
• t = time

When the displacement is directly proportional to the square of time (d ∝ t²), it implies that the second term of the equation, which contains the (1/2)at² part, dominates the relationship. Thus, the initial velocity (u) is typically zero or negligible, making the entire displacement dependent on how time squared interacts with acceleration.

Therefore, the car is moving with uniform acceleration.

Detalhes da Resposta

When a charged ebonite rod is brought near a charged glass rod, there will be attraction. This is because charged objects obey the fundamental principle of electrostatics, which states that opposite charges attract each other while like charges repel each other.

An ebonite rod typically acquires a negative charge when rubbed with fur, as it gains electrons. In contrast, a glass rod usually acquires a positive charge when rubbed with silk, as it loses electrons. Therefore, when these two objects, one negatively charged and the other positively charged, are brought near each other, the opposite charges will attract.

Detalhes da Resposta

To understand the color of a red rose under a blue light, we need to consider how we perceive color. Objects appear colored because they reflect certain wavelengths of light. A red rose appears red in white light because it reflects red wavelengths and absorbs others.

When you shine blue light on a red rose, the situation changes. A blue light primarily contains blue wavelengths. Since the red rose does not have red wavelengths to reflect anymore, and it cannot reflect blue light (as it absorbs it), the rose will appear to be the absence of any reflected wavelength visible to our eyes.

This means the rose will appear black under blue light, as black is perceived when no visible light is reflected into our eyes. Thus, the color of the red rose under a blue light is black.

Detalhes da Resposta

The property by which a material returns to its original shape after the removal of force is called Elasticity.

Let's break it down:

Elasticity: This is a property of a material that allows it to return to its original shape or size after the force that caused deformation is removed. Think of a rubber band—you can stretch it, but once you let it go, it snaps back to its initial shape.

Ductility: This property refers to a material's ability to be stretched into a wire. For example, materials like copper are ductile because they can be drawn into thin wires without breaking.

Malleability: This is a material's ability to withstand deformation under compressive stress. It is the property that allows metals to be hammered or rolled into thin sheets. Gold is a good example of a malleable metal.

Plasticity: This property describes the material's ability to undergo permanent deformation without breaking. When a plastic region is reached, the material will not return to its original shape after the removal of force.

Therefore, when we speak of a material returning to its original shape after the removal of force, we are specifically referring to Elasticity.

Detalhes da Resposta

When you push a wheelbarrow inclined at an angle to the horizontal, the applied force can be divided into two components: a **horizontal component** and a **vertical component**. To find the horizontal component of the force, you need to use the concept of resolving vectors.

The force of 150N is acting at an angle of 60º to the horizontal. The horizontal component of this force can be calculated using the cosine of the angle. The formula to determine the horizontal component \( F_{\text{horizontal}} \) is given by:

F_horizontal = F_applied \times \cos(\theta)

Where:

• F_applied is the magnitude of the applied force, which is 150N.
• \(\theta\) is the angle of inclination to the horizontal, which in this case is 60º.

Substitute the values into the formula:

F_horizontal = 150N \times \cos(60º)

We know that \(\cos(60º)\) equals 0.5.

Therefore:

F_horizontal = 150N \times 0.5 = 75N

Thus, the **horizontal component** of the applied force is 75N.

Detalhes da Resposta

To calculate the speed of sound, we need to understand that an echo involves a sound wave traveling to a surface and back. In this case, the sound travels from the boy to the wall and then returns.

The total distance that the sound wave travels is twice the distance from the boy to the wall because it goes to the wall and back. Therefore, the total distance is:

Total Distance = 2 x 408m = 816m

The echo was heard 2.4 seconds after the sound was made. The speed of sound can be calculated using the formula:

Speed of Sound = Total Distance / Time

Plugging in the values, we have:

Speed of Sound = 816m / 2.4s

When you perform the division, you find:

Speed of Sound = 340 m/s

Thus, the speed of the sound is 340 m/s, which is the correct answer.

Detalhes da Resposta

To determine the inductive reactance of a coil, we use the formula:

Inductive Reactance (X_L) = 2πfL

Where:

• X_L is the inductive reactance, measured in ohms (Ω)
• π is a constant approximately equal to 3.14159
• f is the frequency of the AC source, measured in hertz (Hz)
• L is the inductance of the coil, measured in henrys (H)

Given:

• Inductance (L) = 7 H
• Frequency (f) = 50 Hz

Substituting the given values into the formula:

X_L = 2 × π × 50 × 7

Calculating this:

X_L = 2 × 3.14159 × 50 × 7

X_L ≈ 2 × 3.14159 × 350

X_L ≈ 2 × 1099.557

X_L ≈ 2199.114

Therefore, the inductive reactance of the coil is approximately 2200Ω.

Detalhes da Resposta

To calculate the real depth of a swimming pool given the apparent depth, we can use the concept of refraction of light. When light passes from one medium to a denser medium, it bends towards the normal. This bending effect causes objects submerged in water to appear closer to the surface than they actually are. The formula to relate these depths is given by:

Real Depth = Apparent Depth × Refractive Index

Given the problem:

• Apparent Depth = 10 cm
• Refractive Index of water = 1.33

Using the formula:

Real Depth = 10 cm × 1.33

Calculating the above:

• Real Depth = 13.3 cm

Therefore, the depth of the swimming pool is 13.3cm.

Detalhes da Resposta

To solve this problem, we need to calculate the specific latent heat of vaporization of the liquid. The specific latent heat of vaporization, denoted as \(L\), is defined as the amount of heat required to convert 1 kilogram of a liquid into a gas at constant temperature and pressure. The formula for specific latent heat of vaporization is given by:

L = \(\frac{Q}{m}\)

Where:

• Q is the heat supplied to the liquid (in joules)
• m is the mass of the liquid that is evaporated (in kilograms)

First, we need to calculate the total heat energy \(Q\) generated by the resistor. The heat produced by an electrical resistor can be calculated using the formula:

Q = I^2Rt

Where:

• I is the current (in amperes)
• R is the resistance (in ohms)
• t is the time for which current is flowing (in seconds)

Given:

• I = 10 A
• R = 2 Ω
• t = 20 s

Substituting these values into the formula for Q:

Q = (10^2) * 2 * 20 = 100 * 2 * 20 = 4000 J

Now that we have the total heat energy supplied, let's calculate the specific latent heat of vaporization:

Given that the mass \(m\) of the liquid evaporated is \(5 \times 10^{-3}\) kg, we can substitute the values into the formula for \(L\):

L = \(\frac{4000}{5 \times 10^{-3}} = \frac{4000}{0.005} = 800,000 J/kg\)

Therefore, the specific latent heat of vaporization of the liquid is 8.0 x 10⁵ J/kg.

Detalhes da Resposta

To solve this problem, we need to understand the relationship between tension and frequency in a sonometer wire. The frequency of a vibrating string, such as one in a sonometer, is directly proportional to the square root of the tension in the string. Mathematically, this relationship is expressed as:

f ∝ √T

Where f is the frequency and T is the tension. In the given problem, the original frequency is 50 Hz, and the tension is increased to four times its original value. Let's analyze how this change in tension affects the frequency:

- Original tension = T

- New tension = 4T

Substitute the new tension into the formula:

f_new = 50 Hz × √(4T/T)

Simplify the equation:

f_new = 50 Hz × √4

f_new = 50 Hz × 2

f_new = 100 Hz

Thus, when the tension is four times the original tension, the new frequency of the sonometer's fundamental note becomes 100 Hz.

Detalhes da Resposta

When a body moves in a straight line from one point, such as point P, to another point, such as point Q, the motion is called Translational Motion. This kind of motion refers to an object moving along a path in which every part of the object takes the same path as a reference point. This means that if you follow any point on the body, it covers the same amount of distance in the same time frame as any other point.

Let's break down the other options:

• Rotational Motion: This occurs when an object spins around an internal axis. For example, the rotation of the Earth on its axis is a rotational motion.


• Simple Harmonic Motion: This is a type of periodic motion where the restoring force is directly proportional to the displacement. An example of this is a pendulum swinging back and forth.


• Circular Motion: This occurs when an object moves along a circular path. For instance, the motion of the planets around the sun is circular motion.

In conclusion, since the body is moving from point P to point Q along a straight line, it exhibits Translational Motion.

Detalhes da Resposta

To calculate the monthly electrical bill, we first need to determine the total energy consumption of the household in kilowatt-hours (kWh). Here are the steps:

1. Calculate the total power consumption of the appliances daily:

• The appliances' power ratings are 80W, 100W, and 120W.
• Total power consumption: 80W + 100W + 120W = 300W.

2. Convert the daily power consumption from Watts to kilowatts (kW):

• Since 1kW = 1000W, the daily power consumption in kW is 300W / 1000 = 0.3 kW.

3. Calculate the energy used daily in kWh:

• The appliances are used for 6 hours daily.
• Energy used daily: 0.3 kW * 6 hours = 1.8 kWh.

4. Calculate the monthly energy consumption:

• An average month is 31 days.
• Monthly energy consumption: 1.8 kWh/day * 31 days = 55.8 kWh.

5. Calculate the cost based on the rate:

• The cost of electricity is ₦24.08 per kWh.
• Monthly electricity cost: 55.8 kWh * ₦24.08 = ₦1343.664.

Therefore, the monthly electrical bill is approximately ₦1343.66k.

Detalhes da Resposta

To determine the efficiency of a cell with an internal resistance of 2 Ω while supplying current to a 6 Ω resistor, we can use the concept of power dissipation. Efficiency in this context is the ratio of the power delivered to the external resistor to the total power supplied by the cell. It can be calculated using the formula:

Efficiency (%) = (Power across load resistor / Total power output by cell) × 100

Let's break it down step by step:

• Step 1: Total Resistance - The total resistance in the circuit is the sum of the internal resistance and the resistance of the external resistor:
• Total Resistance (R_total) = Internal Resistance (R_internal) + External Resistance (R_load)
• R_total = 2 Ω + 6 Ω = 8 Ω
• Step 2: Current Calculation - The current flowing through the circuit can be calculated using Ohm's Law, which states V = IR. Assume the electromotive force (EMF) of the cell is E volts:
• Current (I) = E / R_total
• I = E / 8 (Note: We keep E as a variable as it cancels out in the efficiency equation)
• Step 3: Power Delivered to Load - The power delivered to the external resistor can be calculated as:
• Power_load = I² × R_load
• Power_load = (E/8)² × 6
• Step 4: Total Power Supplied by the Cell - The total power supplied by the cell is given by:
• Power_total = EMF × Current = E × (E/8)
• Power_total = E² / 8
• Step 5: Calculate Efficiency: Finally, plug in the power values into the efficiency formula:
• Efficiency (%) = [(E/8)² × 6 / (E² / 8)] × 100
• Simplify to Efficiency (%) = [(6/8)] × 100 = 0.75 × 100 = 75%

The efficiency of the cell when supplying current to a 6 Ω resistor with an internal resistance of 2 Ω is 75%.

Detalhes da Resposta

The force of attraction between molecules of the same substance is called cohesion.

To understand this simply:

Cohesion refers to the attractive forces acting between similar molecules. For example, water molecules attract each other due to hydrogen bonding, which is a strong intermolecular force.

Let's break down some important concepts:

• Cohesion: This force is responsible for phenomena like water forming droplets and the surface tension that allows some insects to walk on water.
• Capillarity: This is not related to cohesion directly, but rather to the movement of liquid within narrow spaces without the assistance of external forces, usually due to a combination of cohesion and adhesion.
• Adhesion: This is the force of attraction between unlike molecules, such as water sticking to the surface of a glass.
• Surface Tension: While related to cohesion, this specifically refers to the effect caused by cohesive forces at the surface of a liquid, which makes the surface act like a stretched elastic membrane.

In summary, **cohesion** is the force that keeps the molecules of the same substance, like water, attracting each other.

Detalhes da Resposta

During the process of glycolysis, a single glucose molecule is broken down into two molecules of pyruvate. During this metabolic pathway, there is a net gain of adenosine triphosphate (ATP) molecules. To understand how many ATP molecules are produced, let's break it down step by step.

1. **Initial ATP Investment:** Glycolysis initially requires an investment of 2 ATP molecules to phosphorylate glucose and convert it into a more reactive form during the early stages of the glycolytic pathway.

2. **ATP Production:** As glycolysis progresses, a total of 4 ATP molecules are produced. This occurs in the later steps of the pathway where adenosine diphosphate (ADP) is phosphorylated to form ATP. This is known as substrate-level phosphorylation.

3. **Net ATP Gain:** To find out the net gain of ATP through glycolysis, simply subtract the initial ATP investment from the total ATP produced:

Net ATP = Total ATP produced - Initial ATP investment

Net ATP = 4 ATP - 2 ATP

Net ATP = 2 ATP

Thus, the net total number of ATP produced during glycolysis is 2 molecules.

Detalhes da Resposta

To calculate the quantity of heat absorbed or released by a substance, we can use the formula:

Q = C × ΔT

where:

• Q is the quantity of heat.
• C is the thermal capacity of the substance.
• ΔT is the change in temperature.

Given:

• C = 400 J/°C
• Initial temperature = 60°C
• Final temperature = 80°C

First, calculate the change in temperature:

ΔT = Final temperature - Initial temperature = 80°C - 60°C = 20°C

Now, substitute the values into the formula to find the quantity of heat:

Q = 400 J/°C × 20°C

Calculate the answer:

Q = 8000 J

Since the options provided are in kilojoules (KJ), we need to convert joules (J) to kilojoules (1 KJ = 1000 J):

Q = 8000 J ÷ 1000 = 8 KJ

Therefore, the quantity of heat for the copper rod, given the specified conditions, is 8 KJ.

Detalhes da Resposta

The degree of precision of a vernier caliper is actually the **smallest value** that the vernier scale can measure, which can be considered as the resolution or least count of the instrument. The degree of precision for most standard vernier calipers is 0.01 cm (or 0.1 mm). This means that the caliper can measure dimensions down to a hundredth of a centimeter.

To understand why this is the case, consider the construction of a vernier caliper:

• The main scale is similar to a ruler, usually graduated in centimeters and millimeters.
• The vernier scale, which moves with the sliding jaws, is marked such that some small fraction of its divisions aligns with one division on the main scale.

This alignment allows more precise measurements than the main scale alone. If the vernier scale has 10 divisions which coincide over a length equal to 9 divisions on the main scale, then each division of the vernier scale represents an extra 0.01 cm. Therefore, it allows measuring smaller intervals between the main scale markings very precisely.

Thus, you won't find vernier calipers with a degree of precision of 0.005 cm, 0.1 cm, or 1.0 cm as options in standard practice for precise measurement tools.

Detalhes da Resposta

An insulator is a material that has a very large energy gap between its valence band and conduction band. To understand this, let's first consider the concept of energy bands: In materials, electrons exist in different energy levels. These levels form bands called the valence band and the conduction band. A material is classified based on the size of the energy gap between these bands.

• Insulator: The energy gap is very large, which means electrons in the valence band require a lot of energy to jump to the conduction band where they can freely move. Because of this large gap, insulators do not conduct electricity well.
• Conductor: The valence band and conduction band overlap or have a very small gap, so electrons can move freely without requiring significant additional energy. Conductors actively conduct electricity.
• Semiconductor: The energy gap is moderate, which means some energy is required for electrons to move from the valence band to the conduction band. Semiconductors can conduct electricity under certain conditions, like when energy (in the form of heat or light) is provided.
• Intrinsic semiconductor: This is a pure type of semiconductor with no added impurities. It behaves like a semiconductor, having a moderate energy gap.

Thus, insulators have a very large energy gap band, making them poor conductors of electricity.

Detalhes da Resposta

A rectifier is a device that changes alternating current (A.C) to direct current (D.C). Alternating current is the type of electrical current that changes direction periodically, while direct current flows in a single, constant direction.

Rectifiers are essential in numerous electrical devices, particularly those that require a stable and consistent power supply. For example, most electronic devices like mobile phone chargers, laptop adapters, and televisions operate on D.C. power, and rectifiers convert the household A.C. power supply to D.C. so that these devices can function properly.

In summary, a rectifier converts A.C., which is alternating power supply, into D.C., which is a steady flow of electricity in one direction, making it usable for electronic devices and various applications that require direct current.

Detalhes da Resposta

The average translational kinetic energy of gas molecules is directly related to the temperature of the gas. This relationship is based on the principles of kinetic molecular theory, which explains the behavior of gas molecules in terms of their motion.

Let's break this down simply:

1. Temperature and Kinetic Energy:

The average translational kinetic energy of gas molecules is given by the equation:

\( KE_{avg} = \frac{3}{2} k_B T \)

where \( KE_{avg} \) is the average translational kinetic energy, \( k_B \) is the Boltzmann constant, and \( T \) is the absolute temperature in Kelvin. This formula shows that the kinetic energy is directly proportional to the temperature.

2. What This Means:

As the temperature of a gas increases, the molecules move faster, which increases their translational kinetic energy. Conversely, as the temperature decreases, the molecules slow down, resulting in lower kinetic energy.

It is important to note that this relation is independent of the pressure and the number of moles of the gas. While pressure and the number of moles do affect the overall behavior of a gas, they do not directly influence the average translational kinetic energy of individual molecules.

Therefore, the correct explanation is that the average translational kinetic energy of gas molecules depends on temperature only.

Detalhes da Resposta

Fat is the food nutrient with the highest energy value, providing 9 calories per gram, while carbohydrates and proteins provide 4 calories per gram. 

Fat is the body's most concentrated source of energy, providing more than twice as much potential energy as carbohydrates or proteins.However, carbohydrates burn fastest in metabolism. Fats are a type of lipid. Lipids are a group of organic compounds that are insoluble in water but soluble in organic solvents. Fats are solid at room temperature, while oils are liquid at room temperature. 

Therefore, the correct answer is option C.

Detalhes da Resposta

At absolute zero temperature, which is defined as 0 Kelvin or -273.15 degrees Celsius, the energy of molecular motion ceases. This means that the molecules theoretically have minimal energy, and hence, their motion stops entirely. Therefore, the average velocity of the molecules is zero. In reality, absolute zero is a theoretical limit, and it is practically unreachable, but it serves as a concept to help in understanding the behavior of molecules at extremely low temperatures. Thus, under this theoretical condition, the average motion of molecules would be nonexistent. In summary, the average velocity of the molecules at absolute zero is zero.

Detalhes da Resposta

The gravitational force between two objects is determined by Newton's Law of Universal Gravitation, which can be expressed by the formula:

F = G * (m1 * m2) / r²

where F is the gravitational force, G is the gravitational constant, m1 and m2 are the masses of the objects, and r is the distance between the centers of the two objects.

In this problem, it is given that the initial gravitational force is 10N. According to the formula, the gravitational force is inversely proportional to the square of the distance between the two objects.

So, if the distance between the objects is halved (i.e., r becomes r/2), then the new gravitational force F' can be calculated based on the relationship:

F' = G * (m1 * m2) / (r/2)² = G * (m1 * m2) / (r²/4) = 4 * (G * m1 * m2 / r²) = 4 * F

Since the initial force F was 10N, the new force F' when the distance is halved is:

F' = 4 * 10 = 40N

Thus, the new value of the gravitational force is 40N.

Detalhes da Resposta

For Hare's apparatus

Relative density = hwhl $\frac{h_w}{h_l}$

Given: height of liquid = 0.5cm, height of water = 0.3cm

Relative density = 0.30.5 $\frac{0.3}{0.5}$ = 0.6

Detalhes da Resposta

Hot wire ammeters measure current by detecting the heat produced in a wire due to the electric current flowing through it.

Detalhes da Resposta

To find the area expansivity of a metal when given its cubic expansivity, you should understand the relationship between linear, area, and cubic expansivity.

Cubic expansivity (\( \beta \)) is defined as the fractional change in volume per change in temperature, and is given by the formula:

\[ \Delta V = \beta V \Delta T \]

Area expansivity (\( \alpha_{A} \)) corresponds to the fractional change in area per change in temperature and can be derived from the linear expansivity (\( \alpha \)). The relationship between these expansivities is as follows:

\[ \text{Area Expansivity (\( \alpha_{A} \))} = 2 \times \text{Linear Expansivity (\( \alpha \))} \]

The cubic expansivity (\( \beta \)) is related to the linear expansivity by:

\[ \text{Cubic Expansivity (\( \beta \))} = 3 \times \text{Linear Expansivity (\( \alpha \))} \]

Thus, based on these relationships, we can express the area expansivity in terms of the cubic expansivity:

\(\text{Area Expansivity (\( \alpha_{A} \))} = \frac{2}{3} \times \text{Cubic Expansivity (\( \beta \))}

Given that the cubic expansivity \( \beta \) is \( 3.9 \times 10^{-6} \, \text{K}^{-1} \):

The area expansivity can be calculated as follows:

\[ \text{Area Expansivity (\( \alpha_{A} \))} = \frac{2}{3} \times 3.9 \times 10^{-6} \, \text{K}^{-1} = 2.6 \times 10^{-6} \, \text{K}^{-1} \]

Therefore, the **correct answer** is **2.6 x 10^{-6} K^{-1}**.

Detalhes da Resposta

To determine the effort needed to lift a load using a machine, we first need to understand some key concepts: **Load**, **Effort**, **Velocity Ratio** (VR), and **Efficiency**.

1. **Load** is the force or weight that needs to be lifted by the machine. In this case, the load is 300N.

2. **Velocity Ratio (VR)** is the ratio of the distance moved by the effort to the distance moved by the load. Given here as 2.

3. **Efficiency** of a machine is expressed as a percentage and is the ratio of the useful work output to the input work done by the effort. Here, the efficiency is 60% or 0.60 as a decimal.

The formula to calculate the **Effort** is derived from the relationship between these factors:

\[ \text{Efficiency} = \frac{\text{Mechanical Advantage (MA)}}{\text{Velocity Ratio (VR)}} \]

Where:

\[ \text{Mechanical Advantage (MA)} = \frac{\text{Load}}{\text{Effort}} \]

From the above, we have:

\[ \text{MA} = \text{VR} \times \text{Efficiency} \]

Replacing with the given values:

\[ MA = 2 \times 0.60 = 1.2 \]

Now, calculate the **Effort** using the relation:

\[ \text{Effort} = \frac{\text{Load}}{\text{MA}} \]

\[ \text{Effort} = \frac{300N}{1.2} = 250N \]

Therefore, the **Effort** needed to lift the load is 250N.

Detalhes da Resposta

A thermometer that relies on the **thermometric property** of **change in volume with temperature** is the **Liquid-in-glass thermometer**.

Here is why:

1. **Construction**: A liquid-in-glass thermometer consists of a **glass tube** that encloses a small reservoir filled with a **thermometric liquid**, typically mercury or colored alcohol.

2. **Principle of Operation**: As the **temperature** changes, the **volume of the liquid** inside the tube changes. When the temperature rises, the liquid **expands** and moves up the tube. Conversely, when the temperature decreases, the liquid **contracts** and moves down the tube.

3. **Scale Calibration**: The thermometer has graduations marked along the tube, allowing the user to read the temperature by observing the level of the liquid against these scale markings.

Therefore, the liquid-in-glass thermometer operates on the principle that the **volume of a liquid changes with temperature**, making it the correct answer.