Thermal Properties of Matter Quiz

Thermal Properties of Matter

• Heat vs. Temperature:
  • Heat is a form of energy transferred between a system and its surroundings due to temperature difference.
  • Temperature measures the degree of hotness of an object.
  • SI unit of heat is Joule (J).
  • SI unit of temperature is Kelvin (K) or Celsius (°C).
  • Dimensions of heat are [L²M¹T⁻²].
  • Dimensions of temperature are [L⁰M⁰T⁰Θ¹].
  • Heat is measured using a calorimeter.
  • Temperature is measured using a thermometer.

Thermometer Calibration

• Standard temperature intervals are selected for calibration.
• These intervals are easily reproducible.
• The interval is then subdivided into degree intervals.
• Numerical values are assigned to each interval/degree.

Scales of Temperature

• Temperature scales include Celsius, Fahrenheit.
• Relationships exist between these scales.
  • (TF - 32) / 180 = (Tc - 0) / 100

Absolute Zero

• Absolute zero is the temperature at which a gas's pressure would be zero.
• Absolute zero is -273.15 °C.

Thermal Expansion Coefficients

• Relationships exist between coefficients of linear, surface, and volume expansion.
• Linear expansion: 𝐿 = 𝐿₀ (1 + α𝑡) (Where L₀ is the initial length and α is the coefficient of linear expansion)
• Surface expansion: 𝐴 = 𝐴₀ (1 + 2 α𝑡) (Where A₀ is the initial surface area)
• Volume expansion: V = V₀ (1 + 3 α𝑡) (Where V₀ is the initial volume)

Applications of Thermal Expansion

• Thermometers: Expansion of liquids (like mercury) measures temperature.
• Removing tight lids: Heating expands the metal cap, making it easier to open.
• Fitting steel wheels on axles: Expanding the wheel and cooling it locks it securely in place.

Specific Heats of Gases

• Two specific heats are considered for gases: at constant pressure (Cp) and constant volume (Cv).
• Cp is greater than Cv.
• This is because at constant pressure, gas does work on surroundings requiring additional heat.

Freezing and Melting Points

• Freezing point and melting point are the same temperature.
• Freezing point is when liquid becomes solid.
• Melting point is when solid becomes liquid.

Sublimation

• Sublimation is the change from solid to vapor state without passing through the liquid state.

Steady State

• Steady state refers to a condition where the temperature of each part of an object (like a metal rod) does not change with time, even as heat continues to flow.
• A rod's temperature is constant at each point across it but not the same across the length of the rod.

Thermal Conductivity

• Thermal conductivity is the rate of heat conduction through a material.
• It is dependent on the distance between the two areas, the area itself, the time, and the temperature difference.
• Mathematically, Q = (K * A * (T₁-T₂)*t) / x (where Q is the rate of heat transfer, k is thermal conductivity, A is area, T₁ and T₂ are the temperatures, t is time, and x is distance).

Applications of Thermal Conductivity

• Cooking utensils are often made of metals (good conductors) but have handles of poor conductors to protect from burns.
• Ice does not melt easily in sawdust, as sawdust is a poor conductor preventing rapid heat conduction to the ice.
• Electric irons have mica coatings: good conductors of heat, but bad conductors of electricity to protect from shocks.

Thermal Resistance

• Thermal resistance is the opposition of a substance to heat flow.
• RT = x / (K * A).

Heat Transfer via Radiation

• Heat can be transferred through radiation without a medium (e.g., from the sun).

Newton's Law of Cooling

• The rate of heat loss is proportional to the difference in temperature between the object and its surroundings, if the temperature difference is small.

Thermal Stress

• Thermal stress arises when material expansion is restricted.
• Gaps are left in structures (like bridges and roads in hot climates) to prevent thermal stress damage.

Thermal Insulators

• Materials with high thermal resistance are poor conductors and good insulators (e.g., glass, wood, rubber, plastic).