Olympiad Test: Heat And Temperature -1 - Class 7 MCQ

Heat energy flows:
- Heat energy always flows from a body at a higher temperature to a body at a lower temperature. This is known as the second law of thermodynamics.
- The flow of heat energy occurs due to the difference in temperature between two bodies. The energy transfer is always from the hotter body to the colder body.
- The transfer of heat can occur through three main mechanisms: conduction, convection, and radiation.
- Conduction: Heat transfer through direct contact between two objects or substances. The heat energy flows from the higher temperature object to the lower temperature object.
- Convection: Heat transfer through the movement of fluids or gases. The hotter fluid or gas rises and transfers heat to the cooler regions, creating a circulation pattern.
- Radiation: Heat transfer through electromagnetic waves. This type of heat transfer does not require a medium and can occur through vacuum as well. Heat energy is radiated from a hotter object to a cooler object.
- When the temperature of two bodies is equal, there is no net flow of heat energy between them. At this point, they are said to be in thermal equilibrium.
- It is important to note that heat energy flows due to the temperature difference and not the amount of substance present in the bodies.
- Therefore, the correct answer is Option A: Heat energy flows from a body at a higher temperature to a body at a lower temperature.

Given:
- One glass of water at 40°C
- Another glass of water at 60°C
To find:
- The temperature of the mixture
Explanation:
- When two substances at different temperatures are mixed, heat flows from the hotter substance to the colder substance until they reach thermal equilibrium.
- The final temperature of the mixture will be somewhere between the initial temperatures of the two substances.
Calculating the final temperature:
- We can use the principle of conservation of energy to calculate the final temperature of the mixture.
- The amount of heat lost by the water at 60°C is equal to the amount of heat gained by the water at 40°C.
- The heat gained or lost can be calculated using the formula Q = mcΔT, where Q is the heat gained or lost, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature.
- Since both substances are water, they have the same specific heat capacity, which is approximately 4.18 J/g°C.
- Let's assume the masses of the two glasses of water are equal for simplicity.
- The heat lost by the water at 60°C is equal to the heat gained by the water at 40°C.
- Therefore, mcΔT = mcΔT.
- Plugging in the values, we get (60- Tf) = (Tf - 40), where Tf is the final temperature of the mixture.
- Solving the equation, we get 2Tf = 100, which gives Tf = 50°C.
Conclusion:
- The temperature of the mixture will be 50°C, which is between 40°C and 60°C.
- Therefore, the correct answer is option C: between 40°C and 60°C.

The degree of hotness or coldness of a body is measured by its temperature.

• Temperature: Temperature is a measure of the average kinetic energy of the particles in a body. It determines how hot or cold an object feels to touch.


• Energy: Energy is a general term that refers to the ability to do work or cause change. While temperature is related to the energy of the particles in a body, it is not a direct measure of hotness or coldness.


• Radiation: Radiation refers to the emission or transmission of energy in the form of waves or particles. While radiation can be used to transfer heat, it is not a measure of the hotness or coldness of a body.


• Heat: Heat is a form of energy that is transferred between objects or systems due to a temperature difference. It is related to the hotness or coldness of a body, but it is not the direct measure of temperature.

Therefore, the correct answer is temperature (D), as it directly measures the degree of hotness or coldness of a body.

Answer:
Mercury is an ideal liquid used in a thermometer because it possesses several key properties that make it suitable for this purpose.
Expansion:
- One of the main reasons mercury is chosen is because it expands significantly when heated. This property allows for accurate measurement of temperature changes.
- When heated, mercury expands uniformly and exhibits a large expansion coefficient compared to other liquids.
- This expansion is easily measurable and translates to a corresponding change in the height of the mercury column in the thermometer.
Non-Stick and Visible:
- Another crucial characteristic of mercury is its non-adhesive nature. It does not stick to the glass walls of the thermometer, ensuring that the measurement is not affected by the liquid adhering to the container.
- Additionally, mercury is highly visible and has a distinctive silver color, making it easy to observe and read the temperature scale accurately.
High Boiling Temperature:
- Mercury has a relatively high boiling point of 356.7°C (674.1°F). This high boiling temperature allows it to remain in a liquid state within the thermometer over a wide range of temperatures, including room temperature and beyond.
Conclusion:
Mercury is an ideal liquid for use in thermometers because it expands significantly when heated, does not stick to glass walls, and has a high boiling temperature. These properties ensure accurate and reliable temperature measurements.

Alcohol has a freezing point much lower than other given substances here.

1 cal = 4.18 joules. 

 

Heat always flows from a hotter region to a colder region. Since iron is a good conductor of heat, more heat will flow from our body to it and we will feel cold. As paper is a bad conductor, less heat will flow from our body. 

The lower fixed point in the Celsius scale is 0ºC, which is the melting point of ice. 

The upper fixed point in the Celsius scale is 100ºC, which is the boiling point of water. 

The chemicals present in the candle burn with oxygen to give out heat. 

Why cooking utensil handles should not conduct heat:

• Handles of cooking utensils should not conduct heat as it can lead to burns or injuries when touched.


• If the handle conducts heat, it can become hot and difficult to hold, increasing the risk of accidents in the kitchen.


• A handle that does not conduct heat will remain cool to touch, making it safe and comfortable to hold while cooking.

Why cooking utensil handles should not radiate heat:

• Handles of cooking utensils should not radiate heat as it can also increase the risk of burns or injuries.


• If the handle radiates heat, it can transfer the heat to the person holding it, causing discomfort or burns.


• A handle that does not radiate heat will ensure that the heat from the cooking utensil does not affect the person holding it.

Conclusion:

Cooking utensil handles should be made of materials that do not conduct heat or radiate heat to ensure safety and comfort while cooking. Materials such as wood, plastic, or heat-resistant materials are commonly used for handles to prevent heat transfer and reduce the risk of accidents in the kitchen.

Metals are better conductors of heat than non-metals. 

Wood is a non-metal and bad conductor of heat. 

Explanation:
Radiation refers to the emission or transmission of energy in the form of waves or particles. It is influenced by several factors, including the color and temperature of the substance. Let's break down each factor:
The color of the substance:
- The color of a substance determines the wavelengths of light it reflects or absorbs.
- Different colors correspond to different wavelengths of light.
- The color of a substance affects the energy of the radiation it emits or absorbs.
The temperature of the substance:
- The temperature of a substance directly affects the amount and type of radiation it emits.
- As the temperature of a substance increases, the intensity of radiation also increases.
- The type of radiation emitted by a substance depends on its temperature. For example, at lower temperatures, a substance may emit mainly infrared radiation, while at higher temperatures, it may emit visible light or even ultraviolet radiation.
Both (a) and (b):
- Both the color and temperature of a substance play a role in determining the characteristics of the radiation it emits or absorbs.
- The color affects the wavelengths of light involved, while the temperature influences the intensity and type of radiation emitted.
Therefore, the correct answer is (c) both (a) and (b).