7 - HEAT

• What is temperature a measure of?

  Degree of hotness or coldness
• What instrument is used to measure temperature?

  Thermometer
• What are thermometric properties?

  Properties that change with temperature
• What are some physical properties that change with temperature?

  • Volume of a liquid
  • Dimensions of a solid
  • Pressure of a gas at constant volume
  • Volume of a gas at constant pressure
  • Electric resistance of a conductor
  • Color of an object
• What is the most common type of thermometer?

  Mercury or alcohol thermometer
• How does a thermometer work?

  Volume of liquid increases with temperature
• What is a thermocouple?

  A thermometer using different metal wires
• What does a thermocouple generate?

  Voltage based on temperature difference
• What is the temperature range a thermocouple can measure?

  -270°C to 2300°C
• Why is platinum used in electrical resistance thermometers?

  It has excellent mechanical and electrical properties
• What does a constant-volume gas thermometer measure?

  Change in gas pressure to measure temperature
• What is absolute zero in Celsius?

  -273.15°C
• What are the main temperature scales?

  • Celsius scale (Centigrade)
  • Fahrenheit scale
  • Kelvin scale
  • Rankine scale
• Who introduced the Kelvin temperature scale?

  William Thompson (Lord Kelvin)
• What is the significance of the triple point of water?

  It is where water coexists in equilibrium
• What is the freezing point of water in Kelvin?

  273.15 K
• What is the boiling point of water in Kelvin?

  373.15 K
• How is temperature reported differently than temperature change?

  • Temperature: e.g., 37 °C
  • Change in temperature: e.g., 2 °C (Celsius degrees)
• What is the relationship between Celsius and Fahrenheit temperature changes?

  5 °C change equals 9 °F change
• How do you convert 98.6 °F to Celsius?

  Use $T_C =$$\frac{5}{9} (T_F - 32)$
• What is the Celsius equivalent of 98.6 °F?

  37.0 °C
• How do you convert -20.0 °C to Fahrenheit?

  Use $T_F =$$\frac{9}{5} T_C +$$32$
• What is the Fahrenheit equivalent of -20.0 °C?

  -4.0 °F
• What is thermal expansion?

  Change in average separation between atoms
• How do most materials behave when heated?

  They expand when heated and contract when cooled
• What is linear thermal expansion of solids?

  • Increase in one dimension due to temperature change
  • Change in length: $\Delta L =$$\alpha L_0 \Delta T$
  • $\alpha$ is the coefficient of linear expansion
• What happens when solids cannot freely expand?

  They experience thermal stress
• What is the formula for stress in materials?

  $Stress =$$\frac{F}{A} =$$\frac{Y \Delta L}{L_0}$
• What happens to a hole in a solid material when heated?

  • The hole expands when heated
  • The hole contracts when cooled
• How do you calculate the change in diameter of a hole in a ring?

  Use $\Delta L =$$\alpha L_0 \Delta T$
• What is the coefficient of linear expansion for gold?

  $14 \times 10^{-6}/°C$
• What is the change in diameter of a gold ring when heated from 27 °C to 49 °C?

  Calculate using $\Delta L =$$\alpha L_0 \Delta T$
• What happens to a hole in solid material when heated?

  It expands when heated.
• How does a hole in a solid material behave when cooled?

  It contracts just like the surrounding material.
• What is the initial temperature of the gold engagement ring?

  27 °C
• How is the change in diameter of the hole in the ring calculated?

  Using the formula $\Delta L =$$\alpha L_0 \Delta T$
• What is the change in the diameter of the hole in the ring?

  $4.6 \times 10^{-6} \text{ m}$
• What is the formula for area thermal expansion?

  • $\Delta A =$$\gamma A_0 \Delta T$
  • $\gamma =$$2\alpha$
• What is the formula for volume thermal expansion?

  • $\Delta V =$$\beta V_0 \Delta T$
  • $\beta =$$3\alpha$
• What is thermal equilibrium?

  Two objects do not exchange energy.