Physics Chapter 7: Heat and Thermodynamics
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Questions and Answers

What is the primary reason for gaps in concrete roadways and sidewalks?

  • To enhance the aesthetic appeal
  • To prevent water accumulation
  • To allow for concrete expansion and contraction (correct)
  • To provide space for vegetation

    • Which mechanism of heat flow involves the transfer of energy through gas molecules colliding with each other?

  • Diffusion
  • Convection (correct)
  • Radiation
  • Conduction

    • What happens when one side of a metal is heated?

  • The metal becomes less dense
  • Heat dissipates into the air
  • The metal melts instantly
  • Heat spreads rapidly through the metal (correct)

    • How does heat from the sun reach the Earth?

    <p>Via electromagnetic waves</p> Signup and view all the answers

    What is the main mechanism by which the Earth loses energy to outer space?

    <p>Radiation</p> Signup and view all the answers

    What is the direction of natural heat flow?

    <p>From higher temperature systems to lower temperature systems</p> Signup and view all the answers

    Which statement best defines entropy?

    <p>The randomness or disorder of a system</p> Signup and view all the answers

    According to the 2nd Law of Thermodynamics, what is the trend related to order and disorder?

    <p>Nature always moves from order to disorder</p> Signup and view all the answers

    Which of the following situations illustrates increased entropy?

    <p>Water evaporating into vapor</p> Signup and view all the answers

    What can be done to lower entropy in a system?

    <p>Doing work by organizing the system</p> Signup and view all the answers

    Which of the following states has the highest entropy?

    <p>Gas</p> Signup and view all the answers

    In terms of particle arrangement, which state has fewer particles and lower entropy?

    <p>Solid</p> Signup and view all the answers

    What does a high degree of disorder in a system indicate?

    <p>Molecules have different speeds and directions</p> Signup and view all the answers

    What is the relationship between the Kelvin and Centigrade temperature scales?

    <p>They are related by the equation $T_K = T_C + 273.15$.</p> Signup and view all the answers

    How do you convert Fahrenheit to Centigrade?

    <p>Subtract 32 and multiply by 5/9.</p> Signup and view all the answers

    What occurs when a red-hot spoon is immersed in warm water?

    <p>Heat flows from the spoon to the water.</p> Signup and view all the answers

    What occurs to most substances when they are heated?

    <p>They expand and their molecules move farther apart.</p> Signup and view all the answers

    What is thermal expansion primarily caused by?

    <p>Rise in temperature causing molecular motion to increase.</p> Signup and view all the answers

    What is the result of heating a metal lid on a glass jar?

    <p>The jar lid expands more than the jar, loosening it.</p> Signup and view all the answers

    What must occur for thermal equilibrium to be reached?

    <p>Heat flows continuously until all substances reach the same temperature.</p> Signup and view all the answers

    In construction, thermal expansion joints are used why?

    <p>To allow for thermal expansion and prevent damage.</p> Signup and view all the answers

    What are the three primary types of molecular motion?

    <p>Vibration, Rotation, and Translation</p> Signup and view all the answers

    What does the kinetic energy of a moving molecule depend on?

    <p>Speed and mass</p> Signup and view all the answers

    Which type of energy is associated specifically with the rotational motion of molecules?

    <p>Rotational energy</p> Signup and view all the answers

    What occurs during the collision of gas molecules?

    <p>Energy is exchanged among kinetic, rotational, and vibrational types</p> Signup and view all the answers

    In solids, what is the only feasible motion present?

    <p>Vibration</p> Signup and view all the answers

    What happens to the thermal energy of a solid when heat is added?

    <p>The atomic vibrations increase</p> Signup and view all the answers

    How is the average thermal energy of a gas typically measured?

    <p>By summing the energies of individual molecules</p> Signup and view all the answers

    What does the equation for average energy in a solid represent?

    <p>The average energy per molecule</p> Signup and view all the answers

    What type of energy is referred to as the thermal energy in a gas?

    <p>Total energy of its moving particles</p> Signup and view all the answers

    Which of the following is NOT a component of the total energy of a gas molecule?

    <p>Gravitational energy</p> Signup and view all the answers

    What is the correct formula for calculating pressure?

    <p>Pressure = Force / Area</p> Signup and view all the answers

    If a gas molecule bounces off the wall of a container, what does it exert on the wall?

    <p>Force</p> Signup and view all the answers

    What unit is used to measure pressure?

    <p>Pascal (Pa)</p> Signup and view all the answers

    A hydraulic system exerts a pressure of 200,000 Pa over an area of 0.2 m². What is the force exerted by the hydraulic system?

    <p>200,000 N</p> Signup and view all the answers

    How much pressure is exerted by a 1000 kg mass over an area of 1 m²?

    <p>100,000 Pa</p> Signup and view all the answers

    Why doesn't a tabletop crack under atmospheric pressure despite the high force it faces?

    <p>The pressure is distributed evenly across the surface.</p> Signup and view all the answers

    If pressure is defined as the force applied over an area, how does increasing the area while keeping the force constant affect the pressure?

    <p>Pressure decreases</p> Signup and view all the answers

    What is the pressure exerted by the atmosphere on a surface area of 2 m², given that atmospheric pressure is 101250 Pa?

    <p>202500 N</p> Signup and view all the answers

    What is the primary focus of thermodynamics?

    <p>Mechanical action and interactions between heat and work</p> Signup and view all the answers

    According to the first law of thermodynamics, what happens to energy in an isolated system?

    <p>It will never increase or decrease</p> Signup and view all the answers

    How is the change in internal energy of a system related to heat and work?

    <p>Change in internal energy equals heat added minus work done</p> Signup and view all the answers

    What happens to temperature between two objects that are not the same temperature?

    <p>Heat flows from the high temperature object to the low temperature object</p> Signup and view all the answers

    What is a consequence of the second law of thermodynamics regarding energy transfer?

    <p>Natural processes involving energy transfer must have one direction</p> Signup and view all the answers

    How does the first law of thermodynamics relate to food energy and movement?

    <p>Food energy allows both work and heat to be released</p> Signup and view all the answers

    What does the first law of thermodynamics imply about mechanical systems?

    <p>The energy input must equal the energy output</p> Signup and view all the answers

    Why are machines unable to achieve 100% efficiency according to the second law of thermodynamics?

    <p>Some energy is always converted to unusable forms</p> Signup and view all the answers

    Study Notes

    Chapter 7: Heat, Temperature and Thermodynamics

    • This chapter covers fundamental concepts in heat, temperature, and thermodynamics.
    • Topics include the definition of heat (thermal energy), temperature, pressure, thermal expansion, the first and second laws of thermodynamics, heat pumps, heat engines, and entropy.
    • This is a broad overview of the topics mentioned in the provided lecture notes, not an exhaustive treatment of each topic.

    Heat, Temperature and Thermodynamics: Outline

    • What is heat (or thermal energy)?
    • What is temperature?
    • What is pressure?
    • Thermal expansion of gases and solids
    • First and second laws of thermodynamics
    • Heat pumps, heat engines, and entropy

    Air, Wind and Molecular Motion

    • Air is mostly composed of nitrogen and oxygen molecules.
    • Average speed of air molecules is approximately 500 m/s (or 1800 km/hr).
    • In a normal day (25°C, normal pressure) there are approximately 2.69 x 1025 molecules in 1m3 or 2.69 x 1016 molecules in 1mm3.
    • The average time between molecular collisions in the atmosphere is approximately 2 x 10-9 seconds.
    • Molecules collide with other molecules 5 x 108 times per second.

    Motion of Molecules in the Air

    • Molecular types and percentages in the air:
      • N2: 78% - Average speed: 450 m/s (1620 km/h)
      • O2: 21% - Average speed: 420 m/s (1500 km/h)
      • Ar: 0.39% - Average speed: 380 m/s (1370 km/h)
      • CO2: 0.03% - Average speed: 357 m/s (1290 km/h)

    Molecular Motion

    • Molecules exhibit three types of motion:
      • Translational motion
      • Rotational motion
      • Vibrational motion
    • Molecules simultaneously move, rotate, and vibrate.

    Energy and Molecular Motion

    • A moving molecule possesses kinetic energy based on its mass and speed (KE = ½mv2).
    • Rotation motion creates rotational energy and vibrational motion creates vibrational energy.
    • During collisions, gas molecules exchange energy among their kinetic, rotational, and vibrational forms.

    Thermal Energy of a Gas

    • Any amount of air contains numerous frequently colliding molecules.
    • Every gas molecule possesses internal energy in the form of kinetic, rotational, and vibrational energies.
    • The total internal energy of a gas molecule is the sum of its various forms of energy.

    Motion and Energy in Solids

    • The only possible mode of motion in solids is vibration.
    • Atoms in solids vibrate around equilibrium positions.
    • Thermal energy in solids is manifested as these vibrations.
    • Increasing heat (thermal energy) increases molecular vibrations.
    • Sufficient heat causes enough vibrations to overcome forces holding components together, causing changes in state (e.g.,melting).

    Thermal Energy of a Gas

    • The total energy of a gas is equal to the total energies of its individual molecules.

    Average Thermal Energy and Temperature

    • Temperature is defined as the average energy of atoms in a system.
    • Temperature is directly proportional to average kinetic energy.
    • Boltzmann constant (kB) is a fundamental constant that relates temperature to energy. (kB=1.38×10-23 J/K)

    Temperature

    • Temperature is a measure of the warmth or coldness of an object.
    • Temperature is measured by a thermometer.
    • Temperature is a per-particle property.

    Thermometer

    • Measures temperature by expansion or contraction of a liquid (mercury or colored alcohol).

    Temperature Scales

    • Celsius scale (0°C for freezing point of water, 100°C for boiling point).
    • Fahrenheit scale (32°F for freezing point of water, 212°F for boiling point).
    • Kelvin scale (0 K for absolute zero, same size degrees as Celsius).

    Temperature Scales and Conversions

    • The Kelvin (K), Celsius (°C), and Fahrenheit (°F) scales are related by equations for conversion between them.

    Heat

    • Heat is defined as the transfer of thermal energy due to a temperature difference.

    Flow of Internal Energy

    • Heat always flows from higher temperature substances to lower temperature substances until thermal equilibrium is reached.

    Thermal Expansion

    • Temperature increases the speeds of molecules, causing expansion.

    Heat Transfer Mechanisms

    • Conduction: Heat transfer by direct contact (e.g., a metal rod).
    • Convection: Heat transfer by the bulk movement of fluids (e.g., air currents).
    • Radiation: Heat transfer by electromagnetic waves (e.g., heat from the sun).

    Pressure

    • Pressure is defined as force per unit area.
    • Pressure is exerted by gas molecules confined in a container due to their collisions with the container walls.

    Examples of Pressure

    • High pressure is related to large areas and low pressure to small areas. A pencil point creates high pressure on a surface.

    Ideal Gas Law

    • The ideal gas law relates pressure, volume, number of moles, and temperature of a gas (PV=nRT).

    Examples

    • Pressure cooking: Uses high temperatures and pressure to cook food faster.

    How Heat Affects State

    • Adding heat to a substance can change its state (e.g., melting a solid, boiling a liquid).
    • Removing heat can also change its state (e.g., freezing a liquid, condensing a gas).

    Thermodynamic Laws

    • 1st Law of Thermodynamics: The total energy of an isolated system remains constant.
    • 2nd Law of Thermodynamics: Heat flows from high to low temperatures. Processes tend towards disorder (entropy increase).

    Entropy

    • Entropy is a measure of disorder. The entropy of a substance increases with the state change from a solid to liquid to gas.

    Order vs Disorder and Entropy

    • Order is associated with fewer particles. Disorder is associated with increased amount of particles.

    More Examples of Entropy

    • Examples using diagrams of different states or situations highlight the concept of entropy.

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    Related Documents

    Chapter 7: Heat, Temperature and Thermodynamics PDF Lecture Notes

    Description

    This quiz explores fundamental concepts of heat, temperature, and thermodynamics as outlined in Chapter 7. It covers key topics such as the laws of thermodynamics, heat engines, and the behavior of air molecules. Perfect for students seeking to deepen their understanding of thermodynamic principles.

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