Content Curator
A cooling curve is a line graph that represents the transition of matter from one phase to another, often from a gas to a solid or from a liquid to a solid.
- On the cooling curve, Time is the independent variable represented in the X-axis, while temperature is the dependent variable represented in the Y-axis.
- Newton's law of cooling states that the rate of cooling of a body is directly proportional to the difference in temperature between the body and its surroundings, provided the temperature difference does not exceed 30°C.
The formula of Newton’s law of cooling is given by
T(t) = Ts + (T0 – Ts) e -kT
Where
- T(t) is the temperature of a given body at time t
- Ts is the temperature of the surrounding
- T0 is the initial temperature of the body
- k is a constant
It is important to know that heat and temperature are not similar. Although the two concepts are related, they have distinct meanings.
- Heat is measured in joules and describes the flow of thermal energy between molecules within a system.
- Heat may be gained or lost by an object, but heat cannot be created.
- Temperature is measured in degrees Celsius (°C), Kelvin (K), and Fahrenheit (°F) and defines the average kinetic energy of molecules inside a substance or system.
Ques. Define temperature.
Ans. Temperature is a physical quantity that measures the degree of hotness or coolness in a body. A thermometer is used to measure temperature. It reflects the kinetic energy of the vibrating and colliding atoms of a substance.
Ques. What is Newton’s Law of Cooling?
Ans. Newton's law of cooling states that the rate of cooling (or rate of heat loss) of a body is proportional to the temperature difference between the body and its surroundings, as long as the temperature difference is small.
Ques. What are the real-life applications of Newton’s Law of Cooling?
Ans. One common application for this concept is wrapping a baby in more woolen garments than an adult. Because the make and rate of fall of temperature are inversely related to each other, a baby loses more heat than an adult who weighs more. As a result, a baby's garments must be wrapped more tightly to avoid heat loss. Similarly, a large plate makes it easier to heat food on a large plate than a bowl. Because the rate of cooling is directly related to volume, a large plate cools and warms quicker than a bowl.
Ques. Define specific heat capacity.
Ans. The specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of one mole of a substance by 1° degree Celsius.
Ques. Why hot milk is easier to drink from a bowl than from a glass.
Ans. Because a bowl has a larger surface area than a glass, more heat is lost to its surroundings through heat radiation through the bowl. The cooling of hot water is determined by the difference between its temperature and the surroundings. The cooling rate is quicker initially, then slows as the temperature drops.
Ques. Define heat energy.
Ans. The movement of small particles known as atoms, molecules, or ions in solids, liquids, and gases produces heat energy. Heat energy can travel from one object to another. Heat is the transfer or movement of energy caused by a temperature difference between two objects.
Ques. The rate of cooling of water increases with a fall in temperature. True or False?
Ans. The above statement is false. The graph of temperature difference with time indicates that as temperature decreases, the rate of cooling (or temperature difference per unit time) also decreases.
Ques. What are the limitations of Newton’s Law of Cooling?
Ans. The limitations of Newton’s law of cooling are
- The temperature difference between the body and the surroundings must be small.
- The loss of heat from the body should only be through radiation.
- The main limitation of Newton's cooling law is that the temperature of the surroundings must remain constant while the body is cooling.
Ques. What is the formula of Newton’s law of cooling?
Ans. The formula of Newton’s law of cooling is given by
T(t) = Ts + (T0 – Ts) e -kT
Where
- T(t) is the temperature of a given body at time t
- Ts is the temperature of the surrounding
- T0 is the initial temperature of the body
- k is a constant
Ques. Which is the fastest mode of heat transfer?
Ans. Because radiation travels at the speed of light, it is the fastest form of heat transmission. Conduction is the slowest means of heat transmission since it occurs from particle to particle.
Ques. Thermal energy is converted to which form of energy in thermal radiation?
Ans. Thermal energy is converted to electromagnetic energy due to the thermal motion of the particles in the material. If a substance's temperature is greater than absolute zero, it emits thermal radiation. Because the velocity of the particles causes charge acceleration, electromagnetic energy is produced by the dipole oscillation of these accelerating charges.
Ques. Name the law that governs the phenomenon of thermal radiation.
Ans. Thermal radiation is governed by the Stefan-Boltzmann Law. According to this rule, the fourth power of a surface's absolute temperature is proportional to the total radiant power emitted by that surface.
Ques. We can use Newton’s law of cooling on a body that is kept in a room containing air at 30°C, and the body’s temperature is 300°C. Is it true or false?
Ans. The given statement is false since Newton's law of cooling can only be used when the temperature difference is small.
Ques. Can you prevent radiation using a good insulator?
Ans. Yes, we can reduce heat radiation by utilizing a shiny or reflective material that reflects heat from the inside and outside of the material or object. A thermos bottle, for example, is covered with a shiny material and has a lining that prevents heat conduction.
Ques. According to which law does the transfer of heat take place?
Ans. The thermal energy per unit temperature that is inaccessible for doing useful work (the total entropy of an isolated system) can never decrease, according to the second law of thermodynamics. As a result, the heat transfer process is explained by the second law of thermodynamics.
Ques. What is heat transfer?
Ans. The phenomena of heat transfer were introduced from the area of thermal engineering to examine the transmission of energy from a high-temperature reservoir to a low-temperature reservoir.
Ques. The walls of deep freezers absorb heat from food items and keep them cool. Which phenomenon is involved in this process?
Ans. The phenomenon of radiation involved in the absorption of heat from food materials by the walls of the deep freezers that keep them cool.
Ques. The amount of heat received by the body when heat is radiated from a hot source depends on the nature of the body. Is it true or false?
Ans. Yes, since radiation is the phenomenon in which heat is transmitted by electromagnetic waves. A black body, for example, will absorb more energy from the same source than any other body.
Ques. Why does the bottom of a lake not freeze in severe winter even when the surface is all frozen?
Ans. In a severe winter, the bottom of a lake does not freeze. Because ice is a poor conductor of heat, once the surface is frozen, no further heat is released or absorbed by water below the ice. As a result, water below ice never freezes.
Ques. Can water stay liquid below zero degrees Celsius?
Ans. When the temperature of an object falls below its freezing point, it normally freezes. Under some conditions, water may remain liquid even at temperatures below 0 degrees Celsius. This is referred to as supercooling.
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