All questions of Heat for Grade 4 Exam

Both (a) and (b)
because It is colour of substances and after coverting into temperature it is answer this question.

Because the normal temperature of human being is 98.6degreeF

The correct answer is option 'B', which states that sea breeze and land breeze are caused by the currents set up in the air due to convection. Let's understand why this is the correct answer in detail.

Sea breeze and land breeze are two different types of local winds that occur near coastal areas. They are both caused by the uneven heating of land and water, which creates a difference in air pressure and sets up convection currents in the air.

Land and water have different heat capacities, which means they absorb and release heat at different rates. During the day, the land heats up faster than the water because it has a lower heat capacity. As a result, the air above the land becomes warmer and rises, creating a region of low pressure.

**Sea Breeze:**

1. During the day, the land heats up faster than the water, causing the air above the land to become warmer and rise. This creates a region of low pressure over the land.

2. The cooler air from the sea, which has a higher pressure, moves towards the land to fill the vacuum created by the rising warm air. This movement of air from the sea to the land is called a sea breeze.

3. As the sea breeze moves inland, it cools the land and provides relief from the heat. It is often accompanied by a gentle breeze and may bring a slight increase in humidity.

**Land Breeze:**

1. At night, the land cools down faster than the water because it has a lower heat capacity. The air above the land becomes cooler and denser, creating a region of high pressure.

2. The warmer air from the sea, which has a lower pressure, moves towards the land to fill the vacuum created by the cooling air. This movement of air from the land to the sea is called a land breeze.

3. The land breeze is generally weaker than the sea breeze and may bring cooler temperatures and drier conditions.

**Convection and Local Winds:**

Convection is the process of heat transfer through the movement of a fluid (in this case, air). The uneven heating of land and water creates temperature differences, which cause the air to rise or sink, setting up convection currents.

In the case of sea breeze and land breeze, the temperature differences between land and water lead to the formation of convection currents in the air. The warmer air over the land rises, creating a region of low pressure, while the cooler air over the water sinks, creating a region of high pressure. This pressure difference causes the air to move from areas of high pressure (sea) to areas of low pressure (land), resulting in the sea breeze and land breeze.

In conclusion, sea breeze and land breeze are caused by the currents set up in the air due to convection. The uneven heating of land and water creates temperature differences, which lead to the formation of convection currents and the movement of air from the sea to the land (sea breeze) during the day, and from the land to the sea (land breeze) during the night.

Wood is a poor conductor of heat (as well as other forms of energy) because it is covalently bound as a compound. As a result, it does not have the free electrons that scatter about to conduct different forms of energy like metals and other strong conductors do.

Explanation:
The odd one out is option C, "We wear dark-coloured clothes in summers."


The other options are related to the concept of heat absorption and radiation, while option C is about personal preference or cultural practice. Let's break down each option to understand why it is the odd one out:
A: Good absorbers are good radiators
- This statement is based on the principle of thermal radiation. Good absorbers of heat also tend to be good radiators of heat. This means that materials that can absorb heat well can also release it efficiently.
B: Shiny surfaces are good reflectors of heat
- Shiny surfaces have a high reflectivity, meaning they reflect a significant portion of the incident heat radiation instead of absorbing it. This property makes shiny surfaces good reflectors of heat.
C: We wear dark-coloured clothes in summers
- This statement is more subjective and based on personal preferences or cultural practices. While it is true that dark-colored clothes can absorb more heat from sunlight compared to light-colored clothes, it is not a universally followed practice in all regions or cultures.
D: Dark colors are good absorbers of heat
- This statement is true and aligns with the concept of heat absorption. Dark colors, such as black, absorb a larger amount of heat compared to lighter colors. This is because dark colors have a higher absorption coefficient for thermal radiation.
Therefore, option C stands out as it is not directly related to the scientific concept of heat absorption and radiation, unlike the other options.

**Explanation:**

Mercury is an ideal liquid used in a thermometer because it possesses several properties that make it suitable for this purpose. Let's discuss each property in detail:

**a) It expands a lot on heating:**
- One of the main properties of a liquid used in a thermometer is that it should expand when heated and contract when cooled. This property allows the liquid to accurately measure changes in temperature.
- Mercury expands significantly when heated, making it an ideal choice for a thermometer. This expansion is linear and predictable, which means that small changes in temperature can be accurately measured.

**b) It does not stick to glass and is visible:**
- Another important property of a liquid used in a thermometer is that it should not stick to the glass and should be easily visible.
- Mercury does not stick to the glass walls of the thermometer, allowing it to freely rise and fall within the capillary tube.
- Additionally, mercury has a silvery appearance, making it highly visible and easy to read.

**c) It has a high boiling temperature:**
- The boiling temperature of a liquid is an important consideration for a thermometer. It should have a high boiling temperature to ensure that it remains in a liquid state within the thermometer's operating range.
- Mercury has a relatively high boiling temperature of 356.7°C (674.1°F), which allows it to remain in a liquid state at high temperatures encountered in everyday applications.
- This property ensures the longevity and accuracy of the thermometer, as the liquid does not evaporate or change state during normal use.

**d) All of the above:**
- Considering all the properties discussed above, mercury possesses all the necessary characteristics to be an ideal liquid used in a thermometer.
- Its expansion on heating, non-stickiness to glass, high visibility, and high boiling temperature make it a reliable and accurate choice for temperature measurement.

In conclusion, mercury is an ideal liquid used in a thermometer because it expands significantly on heating, does not stick to glass, and is highly visible. Additionally, it has a high boiling temperature, ensuring its effectiveness and reliability as a temperature measurement medium.

This is a law of chemistry

D is the answer because degree of hotness or coldness of a body is measured by its temperature.

What is heat

Explanation:


Heat energy is a form of energy that flows from a body at a higher temperature to a body at a lower temperature. This flow of heat energy continues until both bodies reach a state of equilibrium or equal temperature. The direction of the flow of heat energy is always from a body at higher temperature to a body at lower temperature. This is known as the second law of thermodynamics. Heat energy can flow through three different modes: conduction, convection, and radiation.




Conduction:


Conduction is the transfer of heat energy between two objects in direct contact with each other. In this process, heat energy flows from a body at a higher temperature to a body at a lower temperature until both bodies reach the same temperature. For example, when we touch a hot object, heat energy flows from the hot object to our hand until both reach the same temperature.




Convection:


Convection is the transfer of heat energy through a fluid (liquid or gas). In this process, heat energy flows from a body at a higher temperature to the fluid and then to a body at a lower temperature. For example, when we boil water in a pot, heat energy is transferred from the stove to the water through convection.




Radiation:


Radiation is the transfer of heat energy in the form of electromagnetic waves. It does not require any medium and can occur through a vacuum. In this process, heat energy flows from a body at a higher temperature to a body at a lower temperature. For example, the heat energy from the sun reaches the earth through radiation.




Therefore, the correct option is 'A' which states that heat energy flows from a body at a higher temperature to a body at a lower temperature.

Explanation:

Handles of cooking utensils should be made of materials that do not conduct heat. This is because when cooking, the handles can become very hot, and if they are made of a material that conducts heat well, it can become difficult to hold the utensil without getting burned.

Reasons for choosing materials that do not conduct heat:

1. Safety: The primary reason for using materials that do not conduct heat is safety. If the handle becomes hot, it can cause burns or injuries to the person using the utensil.

2. Convenience: When cooking, it is important to have a utensil that is easy to handle. If the handle is too hot, it can become difficult to hold and may cause the cook to drop the utensil, which can lead to spills or other accidents.

3. Durability: Choosing a material that does not conduct heat well can also increase the durability of the handle. If the handle becomes too hot, it can cause the material to weaken or warp, which can reduce the lifespan of the utensil.

Some materials that do not conduct heat well include:

- Plastic
- Wood
- Rubber
- Silicone

Conclusion:

In conclusion, it is important to choose the right material for the handle of cooking utensils. Handles that do not conduct heat well are the safest, most convenient, and durable option. Materials such as plastic, wood, rubber, and silicone are good choices for handles as they do not conduct heat well.

Radiation: The process of the transfer of the heat from one place to another place without heating the intervening medium is called radiation. For example, the heat from the sun reaches the earth through radiation mode. They can reflect and refract like light waves.

Thermoscope is an instrument used to detect radiation of heat. It is typically a thermometer that measures the temperature change in a particular area. It works by using a heat-sensitive material, such as a wax, to detect the presence of heat. This material expands when exposed to heat, and this expansion is used to measure the temperature change.

B is the correct answer