20 Physics -- Rate of Heat Flow

What is the physical meaning of emissivity? Write its unit.

1 Answers

Emissivity is the ratio of a surface’s ability to emit radiant energy compared with the ability of a perfect black body of the same area at the same temperature.

Emissivity (ϵ ) = e/E

Q. With the rise in boiling point of water, the latent heat of steam A. IncreasesB. DecreasesC. Doesn't changeD. Sometimes increases and sometimes decreases

The latent heat of steam also increases. It is because increasing the pressure compresses the expanding molecules of water hence more amount of heat energy is required to overcome the compression and make it boil, same happens in case of change of state, with the increase in pressure, more amount of energy is required for enough expansion of water molecules to change its state. So latent heat of steam also increases.

Justify that there exist a triple point.

1. A closed metal vessel contains water i) at 30 degree celsius and then ii) at 75 degree celcius. The vessel has a surface area of 0.5m^2 and a uniform thickness of 4mm. If the outside temperature...

Explain the transfer of heat by conduction, convection and radiation with examples. b) State their applications in daily life c)How much heat per day is lost by conduction through a concerete wall,...

Heat transfer is the movement of thermal energy from one object or substance to another. The three types of heat transfer are conduction, convection, and radiation. Each type of heat transfer has its own specific characteristics and applications in our daily lives.

Conduction: Conduction is the transfer of heat from one substance to another through direct contact, such as when a hot pan is placed on a cold surface. The heat is transferred from the hotter object to the cooler one until they...

Air is a bad conductor of heat. Why you feel cool without cloth in your body?

Even though air is a bad conductor of heat, it carries away heat from our body due to convection. Hence, we feel cold without clothes.

a) What is meant by a perfect black body? How can you realize such a body in practice? b) Describe idea to estimate the temperature of sun.c) A spherical black body of radius 12cm radiates 450W pow...

The surface temperature of the sun is approximately 6000K . Assuming that the sun radiates like a black body, how much energy does it radiate per second. What would be the solar constant at the ear...

On what factors the thermal conductivity of a solid depends? Descibe Searle's Experimental method to determine thermal conductivity of a solid.

Why are two thin blankets warmer than a single blanket of double the thickness?

Two thin blankets usually warmer than one thick blanket because air is trapped between them. And the air is bad conductor of heat. It doesn’t pass heat from our body to the surroundings.

Calculate the apparent temperature of the sun from the following information:Sun's radius = 7.04 x10^5 km. Distance from Earth: 14.72 x 10^7 km

Which Normally cools faster, a black pot of hot water or a silver pot of hot water? Explain

Water kept insilver pot will cooler faster.

Explanation:

Becausesilver deflects light.In the process it deflects heat.We all know black absorbs light. Sosilver pot is cooler than black pot for the storage of water.People should use silver pots in summer season.

Two bulbs of equal volume are joined by a narrow tube and are filled with a gas at STP. When one bulb is kept in melting ice and the other in boiling water, calculate the new pressure of the gas.

According to Charles' Law, the pressure of a gas is directly proportional to its temperature, provided the volume and the number of moles of the gas remain constant.

Assuming that the two bulbs have equal volumes and contain the same amount of gas, and that the tube connecting them is narrow enough so that the gas behaves as if it were in a single container, we can useCharles' Lawto calculate the new pressure of the gas.

At STP (standard temperature and pressure), the temperature is 0 degrees...

Hot water pipes used in the room are painted black, why?

Hot water pipes are often painted black because black absorbs heat more effectively than other colors. When hot water flows through a pipe, the pipe loses heat to its surroundings. If the pipe is painted black, it will absorb more heat from the hot water, which can help to keep the water hot as it flows through the pipe.

In addition, black absorbs more light than other colors, which makes it a good choice for hot water pipes because it helps to reduce the amount of light reflection from the...