Physics Chapter: Heat Capacity and Specific Heat

Questions and Answers

What is the SI unit of heat capacity?

The SI unit of heat capacity is joule per kelvin (J K-1).

Define specific heat capacity.

Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a substance by 1 K.

Write the equation for calculating heat in terms of mass, specific heat capacity, and change in temperature.

The equation is heat = mass × specific heat capacity × change in temperature.

How does a storage heater maximize energy during off-peak times?

A storage heater uses bricks with high specific heat capacity to store significant heat at lower electricity costs. Signup and view all the answers

Given that the specific heat capacity of copper is 390 J kg-1 K-1, calculate heat lost by 50 g of copper that drops from 94.6 °C to 21.6 °C.

The heat lost is 1423.5 J. Signup and view all the answers

What is the specific heat capacity of water as provided in the context?

The specific heat capacity of water is 4180 J kg–1 K–1. Signup and view all the answers

Explain the purpose of insulation in a storage heater.

Insulation ensures that heat is released slowly and protects users from high temperatures. Signup and view all the answers

How does using a digital thermometer improve the accuracy of temperature measurement in the experiment?

A digital thermometer provides an accuracy of 0.1 °C, reducing potential errors in temperature readings. Signup and view all the answers

What is the significance of ensuring the initial temperature of the metal is below room temperature?

It helps to negate heat gains from the environment before the heating begins, ensuring more accurate measurements. Signup and view all the answers

Why is glycerol used in the experiment rather than another liquid?

Glycerol has a high boiling point, allowing it to efficiently transfer heat to the metal without evaporating. Signup and view all the answers

What role do the voltmeter, ammeter, and stopwatch play in measuring energy supplied?

They are essential for calculating the electrical energy supplied by measuring voltage, current, and time. Signup and view all the answers

Explain how a larger mass of copper would improve the accuracy of heat loss measurements.

A larger mass of copper allows for a more significant amount of heat transfer, leading to clearer temperature changes. Signup and view all the answers

What is the specific heat capacity of water, and why is it significant in thermal calculations?

The specific heat capacity of water is 4200 J kg–1 K–1, and it is significant because it determines how much energy is required to change the temperature of water, affecting processes like heating and cooling. Signup and view all the answers

Describe how convection works in a fluid.

Convection occurs when a fluid is heated, causing it to expand and become less dense, leading it to rise while cooler, denser fluid sinks, creating a circulation pattern. Signup and view all the answers

What factors determine the U-value of a structure?

The U-value is influenced by the thermal conductivity of the materials and the thickness of the structure, measuring heat transfer rate for a temperature difference of 1 K. Signup and view all the answers

Explain the significance of dark surfaces in thermal radiation.

Dark surfaces are more effective at absorbing and radiating heat compared to bright or shiny surfaces due to their higher emissivity. Signup and view all the answers

What is the solar constant, and why is it important for solar energy applications?

The solar constant is approximately 1.36 kW m-2, representing the average amount of solar energy received per square meter at Earth's atmosphere, crucial for designing solar energy systems. Signup and view all the answers

How does the conductivity star experiment demonstrate differences in heat conduction among metals?

The experiment shows that wax on the ends of metal arms melts at different times, indicating that each metal conducts heat at varying rates based on their thermal conductivity. Signup and view all the answers

Describe how the energy supplied to crushed ice could be maintained at a constant rate.

Energy can be supplied at a constant rate using a controlled heat source like a water bath or heat lamp set at a specific temperature, ensuring equal energy delivery. Signup and view all the answers

What happens during the latent heat of fusion, and how is it represented on a temperature vs. energy graph?

During the latent heat of fusion, a substance, like ice, absorbs energy without a temperature change, which is represented as a horizontal line on the graph where temperature remains constant. Signup and view all the answers

Explain the role of convective currents in a hot water system.

Convective currents facilitate the movement of heated water rising to the top of the tank, allowing cooler water to fill in from the bottom, thus enabling effective heating throughout the system. Signup and view all the answers

How does radiation transfer heat differently from conduction and convection?

Radiation transfers heat through electromagnetic waves and does not require a medium, unlike conduction and convection, which require particles to transmit energy. Signup and view all the answers

What is the definition of specific heat capacity?

Specific heat capacity is the amount of heat energy required to raise the temperature of 1 kg of a substance by 1 K. Signup and view all the answers

Calculate the energy absorbed by 5000 kg of water when its temperature increases by 70 K, given the specific heat capacity of water is 4180 J kg–1 K–1.

The energy absorbed is $Q = mc heta = 5000 imes 4180 imes 70 = 1463000000$ J. Signup and view all the answers

What do the terms heat capacity and specific heat capacity refer to?

Heat capacity is the amount of heat needed to change the temperature of an object, while specific heat capacity is that amount per unit mass. Signup and view all the answers

Explain how a heat pump operates using a refrigerant.

A heat pump circulates a refrigerant that absorbs heat from a cooler area and releases it in a warmer area by changing from liquid to gas and back. Signup and view all the answers

What is the latent heat of fusion of ice, and how does it relate to the melting process?

The latent heat of fusion of ice is $3.3 imes 10^5 ext{ J kg}^{-1}$, which is the heat required to convert ice at 0 °C to water at the same temperature. Signup and view all the answers

How can the design of a fulacht fiadh be improved for better efficiency?

Using insulated walls to reduce heat loss and incorporating a better design to maximize heat transfer from the stones to water. Signup and view all the answers

Calculate the highest temperature reached by 750 liters of water heated by stones at 280 °C, using specified heat capacities.

The maximum temperature reached can be calculated using the formula with heat exchanged between stones and water, leading to a calculated final temperature. Signup and view all the answers

Describe the importance of specific latent heat in phase changes.

Specific latent heat dictates how much energy is needed to change the state of a substance, which is crucial during freeze or melt processes. Signup and view all the answers

What are two desirable properties of the refrigerant fluid used in heat pumps?

The refrigerant should have a high specific latent heat of vaporization and a low boiling point. Signup and view all the answers

What method of heat transfer is responsible for the temperature rise in a thermometer when placed near a lamp?

Heat travels by radiation from the lamp to the thermometer. Signup and view all the answers

Explain why perspiration helps to regulate an athlete's body temperature.

When an athlete perspires, the evaporation of sweat from the skin surface cools the body, reducing temperature. Signup and view all the answers

Calculate the average energy falling on an area of 5 m² of ground in Ireland in 1 minute given the solar constant is $1.2 imes 10^2$ W m–2.

The average energy is $36000$ J. Signup and view all the answers

What is the energy loss through a double-glazed window in one hour if the U-value is 2.8 W m–2 K–1, with an area of 3.0 m², inside temperature 20 °C and outside temperature 11 °C?

The energy lost is $76.2$ kJ. Signup and view all the answers

Distinguish between conduction, convection, and radiation as methods of heat transfer.

Conduction is the transfer of heat through direct contact; convection involves heat transfer through fluid movement, while radiation is transfer through electromagnetic waves. Signup and view all the answers

Define the term solar constant.

The solar constant is the amount of solar energy received per unit area at the top of the Earth's atmosphere, typically measured as $1361$ W m². Signup and view all the answers

What observations might a student make in an experiment investigating how heat travels through water?

The student may observe that the temperature of the water increases as heat is applied, indicating heat transfer. Signup and view all the answers

What conclusion could be drawn about the heat transfer in the water experiment?

The conclusion would be that heat energy flows from areas of higher temperature to areas of lower temperature until thermal equilibrium is reached. Signup and view all the answers

How can you calculate the specific heat capacity of water based on the energy supplied during the experiment?

The specific heat capacity can be calculated using the formula $Q = m_w c_w (θ_F - θ_I)$, solving for $c_w$. Signup and view all the answers

What is a precaution to take when conducting an experiment to measure the specific heat capacity of water?

Ensure the water's initial temperature is below room temperature to minimize heat loss to the environment. Signup and view all the answers

How does the high specific heat capacity of storage heater bricks influence their heat retention capabilities?

The high specific heat capacity allows the bricks to absorb a large amount of heat with only a small increase in temperature, enabling them to store significant heat for later release. Signup and view all the answers

Why is it important to consider both heat lost by copper and heat gained by water in thermal equilibrium?

It's essential to consider both factors because, in thermal equilibrium, the heat lost by the hotter substance equals the heat gained by the cooler one, ensuring energy conservation. Signup and view all the answers

Explain the significance of using the specific heat capacity of water in heat calculations.

The specific heat capacity of water is significant because it is a common reference for thermal properties and crucial for calculating energy changes in processes involving water. Signup and view all the answers

How do calorimeters contribute to the measurement of specific heat capacities in experiments?

Calorimeters provide a controlled environment to accurately measure heat transfer between substances, which is critical for determining specific heat capacities. Signup and view all the answers

Describe how the principles of thermal energy transfer are demonstrated in the operation of a storage heater.

Storage heaters operate by absorbing electrical energy as heat during off-peak hours, which is then slowly released throughout the day to maintain room temperature. Signup and view all the answers

What is the relationship between specific heat capacity and the energy required to change the temperature of a substance?

Specific heat capacity is the amount of energy required to raise the temperature of 1 kg of a substance by 1 K, meaning higher specific heat capacity requires more energy for the same temperature change. Signup and view all the answers

How does the latent heat of vaporization affect the conversion of water into steam in a kettle?

The latent heat of vaporization indicates the amount of energy needed to convert water into steam without changing temperature, which allows for efficient boiling in a kettle. Signup and view all the answers

Explain how the design of a fulacht fiadh can be improved for more heat efficiency.

Improving insulation around the water pit and using stones that retain heat longer can enhance the thermal efficiency of a fulacht fiadh. Signup and view all the answers

What role does the expansion valve play in the operation of a heat pump?

The expansion valve lowers the pressure of the refrigerant, allowing it to vaporize at a lower temperature and absorb heat from its surroundings. Signup and view all the answers

In the context of a refrigerator, how does the release of latent heat help in cooling the interior?

When the vaporized refrigerant condenses back into a liquid, it releases latent heat, which transfers heat away from the refrigerator’s interior, leading to cooling. Signup and view all the answers

Study Notes

Heat Capacity and Specific Heat Capacity

Heat Capacity (C): Amount of heat needed to raise a body’s temperature by 1 K.
- Scalar quantity with units J K⁻¹.
Specific Heat Capacity (c): Amount of heat required to raise 1 kg of a substance by 1 K.
- Scalar quantity with units J kg⁻¹ K⁻¹.
- Formula: heat = mass × specific heat capacity × change in temperature.
- Notable values for specific heat capacity:
  - Water: 4180 J kg⁻¹ K⁻¹
  - Copper: 390 J kg⁻¹ K⁻¹
  - Aluminium: 910 J kg⁻¹ K⁻¹

Energy Transfer

Sample calculations illustrate feasibility for energy transfer.
- Using ( Q = mc\Delta \theta ) establishes energy change.

Storage Heaters

Composed of electric heating elements surrounded by bricks with high specific heat capacity.
Heated during off-peak hours, provides efficient heat retention and releases energy slowly throughout the day.

Latent Heat

Latent Heat (L): Heat required to change a body’s state without temperature change.
- Specific latent heat (l) for 1 kg of substance.
Specific Latent Heat of Fusion (l_f): Heat needed to change 1 kg from solid to liquid (e.g., ice: 3.3 × 10⁵ J kg⁻¹).
Specific Latent Heat of Vaporisation (l_v): Heat needed to convert 1 kg from liquid to gas (e.g., water: 2.3 × 10⁶ J kg⁻¹).

Heat Pumps

Devices that transfer energy from cold to warm areas, requiring external work.
Utilize refrigerants with high specific latent heat of vaporisation to evaporate and absorb heat.
Process involves compressing and expanding refrigerant to facilitate heat exchange.

Heat Transfer Methods

Conduction: Heat transfer via molecular vibration; metals are good conductors, insulation materials are poor conductors.
- Demonstrated using conductivity stars and observing wax melting.
Convection: Heat transfer in fluids via circulation; hot fluid rises as cooler fluid replaces it.
- Observed using dye in a liquid to visualize current movement.
Radiation: Heat transfer by electromagnetic waves; dark surfaces are better radiators than shiny ones.

U-value

Quantifies heat conduction through a structure per unit area, decreasing values indicate better insulation.
Measured in W m⁻² K⁻¹.

Solar Radiation and Heating

Solar Constant: Energy from the sun hitting Earth’s atmosphere, approximately 1.36 kW m⁻².
Solar heating systems convert sunlight for domestic water heating and electricity generation using photovoltaic cells.

Practical Applications and Sample Problems

Various calculations provided for specific heat capacities, latent heats, and energy required for heating and state changes.
Offers methodologies for experimental determination of specific heat capacity, highlighting importance of insulation and accurate measurement techniques.

Historical Context

Mention of archaeological practices like fulacht fiadh in ancient Ireland, illustrating early methods of water heating using heated stones.

Importance of Specific Properties

Underlines requirements for materials in heat systems such as high specific heat capacities and proper insulation to enhance efficiency.### Energy Relationships in Calorimetry
Energy supplied equals the sum of heat gained by water and heat gained by calorimeter: ( Q = (mc\Delta \theta)w + (mc\Delta \theta){cal} )
Specific heat capacity of water: 4180 J kg⁻¹ K⁻¹; specific heat capacity of copper: 390 J kg⁻¹ K⁻¹.

Experimental Setup for Specific Heat Capacity

Requires mass measurements of calorimeter, water, and metal, using an electronic balance.
Initial and final temperature readings taken for both water and metal using a digital thermometer.
Insulation is essential to minimize heat transfer with surroundings.

Precautions for Experiments

Maintain initial water temperature below room temperature to negate environmental heat loss/gain.
Use well-insulated calorimeters with lids to minimize heat exchange.
Digital thermometers increase accuracy (0.1 °C precision).
Stirring and thermometer must have low specific heat capacity to minimize experimental errors.

Measurement of Electrical Energy Supplied

Alternatives to joulemeter include voltmeter, ammeter, and stopwatch to measure electric energy.
Energy calculation based on: ( Q = VIt ), where ( V ) is voltage, ( I ) is current, and ( t ) is time.

Determining Specific Heat Capacity of Metal

Calculations based on the equation: ( Q = mc\Delta \theta ).
Significant energy supplied leads to measurable temperature changes, allowing specific heat capacity determination.

Experiment: Specific Latent Heat of Fusion of Ice

Mix warm water and crushed ice in a calorimeter.
Measure mass changes and initial/final temperatures before and after ice melting.
Heat lost by warm water equates to heat gained by melted ice, following conservation of energy principles.

Calculation of Specific Latent Heat

Formula: ( (mc\Delta\theta)w + (mc\Delta\theta){cal} = m_{ice} l_f + m_{ice} c_w (\theta_F - \theta_{ice}) ).
Masses determined through measurements before and after processes, aiding in accurate calculations.

Experiment: Specific Latent Heat of Vaporisation of Water

Steam is introduced to cold water, leading to condensation and energy transfer.
Mass and temperature data recorded to calculate latent heat using conservation principles.
Similar approach to ice experiments, focusing on energy balance and accurate measurements.

General Experimental Notes

Use of sensitive instruments to minimize calculation errors.
Consistency in physical conditions (temperature, steam quality) affirm accuracy.
Importance of methodical data recording for reliable result analysis.

Past Examination Context

Historical significance as topics appear repeatedly in various exam settings highlighting the importance of understanding heat transfer principles.
Questions focus on experimental design, data interpretation, and ensuring quality control via precautions.

Conclusion

Mastery in calorimetry relies on precise measurements, careful energy calculations, and thorough understanding of thermal principles.
Consistent practice with experimental techniques enhances competence in thermodynamics and its applications.