Transfer of heat - class-XI

For one minute

The temperature difference across cylindrical insulation is given by ΔT = Q × ln(r2/r1) / (2πkL), where Q = I²R. For the given values (wire radius 0.32mm, insulation thickness 0.06mm, k=0.16×10⁻², L=200cm, Q=5²×4=100W), the temperature difference works out to approximately 3°C. The insulation thickness is small compared to wire radius, which affects the logarithmic term in the heat transfer equation.

When ice at 0 degrees Celsius is mixed with an equal mass of water at 10 degrees Celsius, the water cools down, releasing heat. However, this available heat is insufficient to melt the entire mass of ice, as the latent heat of fusion for ice is quite high. Consequently, the mixture remains in thermal equilibrium at 0 degrees Celsius with both ice and water present.

This is a knowledge based question; also remember that copper is used in electrical wiring only because it is cheaper than silver; copper has lower conductivity than silver.

Air is a bad conductor of heat, hence if layer of air is isolated between two layers of cloth, warmer covering will be provided than if only one layer of cloth, where only body is isolated from surrounding air by cloth. 

Insulator between the two layers prevent the heat exchange.

Most metals are good conductors of heat and they are solids at room temperature. Mercury is the only one in liquid state at room temperature. It's used in thermometers because it has high coefficient of expansion. Hence, the slightest change in temperature is notable when it's used in a thermometer.

Mercury is categorized under metasl and we know that metals conduct heat better than non-metals.

Poor conductor should be used, so that they will not allow heat to pass from water inside the pipe to outside atmosphere to prevent water from freezing. It will help pipes from busting.

On a cold day when a room temperature is $15^oC$, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of $15^oC$ because metals are good conductor of heat, so they could absorb and release heat in a better way than insulators.

Using the heat conduction formula Q = (KA dT t) / d, where Q is proportional to mass (volume * density), we relate the time taken to melt ice to the thermal conductivity. The ratio of conductivities is derived from the given radii, thicknesses, and times.

The rate of heat transfer through the spheres depends on their specific heat capacity. Since they have equal masses and are heated to the same temperature, the one with the lowest specific heat capacity will transfer heat the fastest to the wax, but the question implies they all melt through at the same time if the heat capacity is not the limiting factor or if the setup is idealized.

The melting point of ice decreases with an increase in pressure. The weight of the glacier creates higher pressure at the bottom, causing the ice to melt there first.

Let the thermal conductivity of first rod be $5 K$

In steady state, the heat flow rate through both layers must be equal. Solving the equation (K1/d1)(T1 - T) = (K2/d2)(T - T2) for T gives the interface temperature.

The statement that the rate of heat loss by radiation is increased due to a metallic surface is incorrect because metallic surfaces (especially smooth ones) have low emissivity, which reduces radiative heat loss. Convection and conduction are standard modes of heat transfer, and heat loss rate naturally decreases as the body approaches ambient temperature.

The rate of cooling (dT/dt) is proportional to the surface area divided by the volume (A/V). For a sphere, A/V = (4pir^2) / ((4/3)pir^3) = 3/r. Since the radius of Q is 3 times that of P, the rate of cooling for P is 3 times the rate for Q (x = 3/1 = 3).

Cooling rate is proportional to the surface area to volume ratio (A/V). For a fixed mass and material, the object with the largest surface area will have the highest rate of heat loss. A thin circular plate has the highest surface area, while a sphere has the lowest surface area for a given volume.

Heat current (dQ/dt) is proportional to thermal conductivity (k). Copper has a much higher thermal conductivity than steel, so a copper rod will conduct heat faster than a steel rod of identical dimensions.

Since glass is bad conductor of heat the heat will try to escape but the glass would not allow it and in the process ultimately glass breaks down.

Free electrons are not associated to any atom in particular. They are usually the valence electrons of the metal atoms and are loosely bound. These electrons form a "charge fluid" that travels from one place to other in the conductor and thus convey electric current.

In the Ingen Hauszs experiment, as rate of heat transfer is constant
$\dfrac { { K } _{ 1 } }{ { K } _{ 2 } } =\dfrac { { l } _{ 1 } }{ { { l } _{ 2 } } } $
So, putting the value in above formula's we find
$\dfrac{{K} _{1}}{{K} _{2}}=\dfrac{10}{25}=\dfrac{1}{2.5}$

Thermocole lined box is used as cold storage because these material is a poor conductor of heat . And it has millions of tiny air bubbles that show the progress of heat through material.

Smaller sphere

${35}^{o}C$ is equivalent to $(273.15+35)308.15K$. So iron ball is at higher temperature and heat will flow from iron ball to the water.

In a room with air, heat transfer occurs via conduction (through the air and objects), convection (movement of air currents), and radiation (electromagnetic waves). All three modes contribute to heat transfer in this environment.

Steel being an alloy of metals, it has free electrons in its atoms. They start moving along with the heat flow and help in the conduction of heat. All metals are good conductors. The other three being non-metals, do not have free electrons. Hence they are bad conductors

All metals are good conductors while non-metals are bad conductors of heat.

When we touch a steel rod and a paper simultaneously in winter, we feel the rod is comparatively colder because steel being a good conductor of heat, heat from our hand flows to steel but there is no transfer of heat from our hand to paper as it is an insulator of heat. So we don't feel cold when we touch a paper but we do when we touch a steel rod.

A thermal conductor is a material that allows energy in the form of heat, to be transferred within the material, without any movement of the material itself. Eg. Metals.

Metals are generally good conductors of heat.
Non - metals are poor conductors of heat.

Water is the poor conductor among all. As it is liquid and liquids generally have low heat conductivity than solids. Tighter the molecules are held, more the vibrational energy can transfer between them, heat is no more than vibrating molecules. If we talk about steam, its molecules are less tightly held. But it's important to note that we are talking here of heat conductivity not convection or radiation and contact surface area with heat source.

Woollen clothes effectively separate the body from surrounding air by entrapping a layer of air.
Since both wool and air are bad conductors of heat on varying levels, it creates separation that keeps bodies warm.

Conductors allow heat to pass through them through vibration of the molecules.

Glass is a bad conductor of heat hence the heat from the upper part of the glass tube will not transfer easily to the lower part. Having said that, even wax is a bad conductor of heat and won't melt easily. 

Silver is the best conductor of heat among the given options.

When the hot tea is poured into the glass tumbler one side of the glass expands while the other side doesn't. Since glass is not a good conductor of heat, it breaks.

Metals are good conductors of heat hence a person might get his fingers injured if he holds the hot plate. 

Cork is a bad conductor of heat rest are good conductors

Insulators are  through which heat cannot pass easily.

Asbestos is an insulator rest are good conductors of heat

Silver is a good conductor of heat rest are bad conductors

Ebonite is a very good insulator while mercury, silver and copper are examples of conductors.

Metals have much lower specific heat than water because metals require smaller amount of energy to raise their temperature than water .

Specific heat capacity is the amount of heat required to raise the temperature of a unit mass by one degree. Materials with low specific heat capacity require less energy to increase their temperature, thus they become hot easily.

In conduction, heat is transferred by the vibrations of molecules. The density of conductors is large, it means molecules are close to each other, because of that they can easily transfer the heat quickly through the whole conductor, therefore unit mass of conductors require small heat to raise their temperature through $1^{o}$ i.e. conductors have very low specific heat. 

$Q=ms\Delta T$,

Conductors have very low specific heat capacity (c) , therefore heat required (Q) to raise their temperature to a certain range is also less by the following relation: $Q\propto c$

Sulphur, Phosphorus, Wood are non-conductors of electricity due to no presence of free electrons in outermost shell.

Conductors can easily conduct electricity because they are loosely bound to the nucleus and they are not engaged in chemical bonding. Conductors have free electrons.

In conductors, electrons can flow because their electrons are free and mobile metals have free electrons present in outermost orbit i.e. they are mobile in nature. This is the fact due to which they could produce electricity.

An electrical insulator is a material whose internal electric charges do not flow freely because of extremely high resistance. Very little electric current will flow through it under the influence of an electric field.

Metals have free electrons which can move from atom to atom easily, whereas non-metals do not, their electrons are 'bound' meaning they cannot move easily. That's why metal are usually good conductors than non-metals.

Pure water or distilled water doesnot conduct electricity but tap water, rain water or sea water conduct electricity. For electricity to travel through a liquid movement of charge must take place through the liquid. In tap water, rain water or sea water, there are impurities such as salt of $Na,Mg ; and ; Ca$. They behave as the charge carriers for conduction of electricity. But in distilled water there are no impurities i.e. no ions. There are only neutral water molecules. So, distilled water doesnot conduct electricity.

Copper is usually used for copper wiring because copper conducts electricity. Because electrical conductivity of copper is good enough and it is cheap too. So it is used in wiring.

Insulators are used in circuits, as they don't conduct electricity, they are used for insulation of wire, switches, plugs, etc. So that circuit could be made shock free and safe to touch.

Electrical plugs are made up of plastic because plastic protects people from electricity. As we know that plastic is an electrical insulator readily available and cheap. So as to make the plugs shock free, they are made up of plastic.

Electrical wiring is usually covered with layer of plastic to make it safe. As we know that plastic is an electrical insulator and it is readily available and cheap. So as to insulate the electricity carrying wire, to make it shock free. It is covered with layer of plastic.

Materials that allow electrons to flow through them are known as conductors because they consist of free electrons.

Pots and pans are NOT example of insulator, they are conductors of heat, if it was not so; they could not be used for cooking of food. And they are used for cooking; so they are conductors.

Scissors made of iron could be used to complete an electrical circuit. As iron is a metal and conductor so can conduct electricity easily. And others are non-metals. So they could not conduct electricity and can't complete the circuit.

Pure water consists of no impurities; impurities such as salts of $Mg,Ca,Na$ are behaving here as charge carriers but since they are not present; there are no ions. They are neutral water molecules. So pure water do not conduct electricity.

Mud is a bad conductor of heat. It does not allow the heat to transfer from house to atmosphere in winter and atmosphere to house in summer.