Heat Energy Class 8 ICSE Physics | Selina Chapter 6 | Thermal Expansion of Solids, Liquids, Gases #2

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Deepika introduces thermal expansion in solids, liquids, and gases, highlighting the increase in size of substances when heated and the different types of expansions involved. Practical applications include rail tracks with gaps to accommodate steel plate expansion and contraction, emphasizing the importance of understanding thermal expansion in daily life.

Insights

  • Heating solids causes them to expand due to weakened intermolecular forces, leading to linear, superficial, and cubical expansion, with different materials expanding at varying rates.
  • Practical applications of thermal expansion include designing structures like bridges and rail tracks to accommodate expansion and contraction, utilizing materials with low expansion limits like Pyrex, and employing thermal expansion in devices like pendulum clocks and mercury thermometers for accurate measurements.

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Recent questions

  • What is thermal expansion?

    Thermal expansion refers to the increase in size of a substance when heated and contraction when cooled.

  • How does linear expansion in solids work?

    Linear expansion in solids involves the increase in length of a material when heated, depending on the original length, temperature, and material composition.

  • What is superficial expansion in solids?

    Superficial expansion in solids refers to the increase in area of a material when heated, dependent on the initial area, temperature, and material properties.

  • What is cubical expansion in solids?

    Cubical expansion in solids involves the increase in volume of a material in all directions when heated, dependent on the initial volume, temperature change, and material characteristics.

  • How are thermal expansion principles applied in daily life?

    Thermal expansion principles are applied in daily life through the construction of structures like bridges with steel girders on rollers, rail tracks with gaps, and riveting techniques using red-hot rivets.

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Summary

00:00

Heat Transfer and Thermal Expansion in Solids

  • Deepika from Learn Hub introduces a session on heat transfer and thermal expansion in solids, liquids, and gases.
  • Thermal expansion refers to the increase in size of a substance when heated and contraction when cooled.
  • Solids, like stones, expand in all directions when heated, leading to linear, superficial, and cubical expansion.
  • At the molecular level, heating solids weakens intermolecular forces, allowing molecules to vibrate more and increase in size.
  • Experimental demonstrations of thermal expansion in solids involve metal balls not passing through rings or bars not fitting into gauges after heating.
  • Linear expansion in solids depends on the original length, temperature, and material of the rod.
  • Longer rods expand more than shorter ones, higher temperatures lead to greater expansion, and different materials expand differently.
  • The formula for linear expansion involves the change in length being proportional to the initial length and temperature.
  • Exceptions to thermal expansion include Nivaralloy and Pyrex glass, which show negligible expansion when heated.
  • Practical experiments to demonstrate linear expansion involve metal rods attached to pointers that move when heated, showcasing thermal expansion.

17:01

Thermal Expansion in Solids: Key Concepts

  • Bending of bimetallism page involves using strips made of two metals, such as brass and iron, which expand differently when heated, causing a curved position.
  • Superficial expansion in solids refers to the increase in area when a metal plate is heated, depending on initial area, temperature, and material.
  • The formula for superficial expansion of solids involves the change in area being directly proportional to initial area and temperature, with a proportionality constant beta.
  • Cubical expansion in solids involves the expansion in all directions, including length, breadth, and thickness, resulting in an increase in volume.
  • The formula for cubical expansion includes the change in volume being directly proportional to initial volume and temperature, with a proportionality constant gamma.
  • Applications of thermal expansion in daily life include the construction of bridges with steel girders on rollers to accommodate expansion and contraction.
  • Rail tracks are laid with a gap between them to allow for expansion and contraction of the steel plates in different temperatures.
  • Riveting involves fixing two iron plates together using a red-hot rivet that contracts upon cooling, securing the plates in place.
  • Electric cables and telephone wires are installed with curves to account for expansion and contraction due to temperature changes.
  • Fitting a steel rim into a wooden wheel involves heating the steel rim to expand it before fitting it around the wooden wheel, allowing it to contract and fit perfectly upon cooling.

33:20

Materials with low expansion for accurate timekeeping

  • Pyrex is recommended for its low thermal expansion limit in applications where expansion is undesirable.
  • Pendulum clocks utilize materials like Ivar with low thermal expansion to maintain accurate timekeeping.
  • The function of a pendulum in a clock is to ensure correct timekeeping by using materials with minimal expansion.
  • To loosen a stuck glass stopper or metal screw cap, heat the neck of the container to expand it for easy removal.
  • Thick glass tumblers can crack when hot liquids cause uneven expansion, leading to breakage.
  • Liquids, like water, exhibit abnormal expansion behavior, expanding only after 4 degrees Celsius.
  • An experiment with a bottle, ink, cork, and straw demonstrates liquid expansion due to heating.
  • The cubical expansion in liquids is influenced by original volume, temperature rise, and the nature of the liquid.
  • Different liquids expand at varying rates when heated, with benzene expanding the most and water the least.
  • Mercury thermometers utilize mercury's expansion to measure temperature changes in the body.

48:50

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