Physics chapter 10 Flashcards
Define thermal expansion?
It is the expansion of matter caused by heating
How is Thermal expansion used in Joining two metals?
A red hot rivet is passed through holes in 2 metal plates and then hammered down until its edges are rounded, when the rivet cools it contracts and pulls the 2 plates tightly together.
How does Gas expand when heated compared to solid?
Solid expands slowly and very little as there is not much room between the particles, however gas expands rapidly as there is more space between the particles.
Define Thermal capacity?
The number of heat units needed to raise the temperature of a body by one degree.
Define specific heat capacity?
The energy required per kilogram and per degree Celsius to raise the temperature of a substance.
Formula for Specific heat capacity?
Thermal capacity(joules) / Mass(kg)
Formula for energy required to heat an object?
Mass * Specific Heat capacity * Temperature change
What is the specific heat capacity of water?
4200 J/kg degrees C
Explain melting?
When a solid is heated, its particles gain more kinetic energy and vibrate faster and faster, until it reaches a certain temperature known as the melting point, at witch point the particles will have enough energy to break away from the forces of attraction and from one another, becoming liquid.
Define freezing?
When a liquid is cooled, the particles release thermal energy. The particles start moving and vibrating slower until at a certain temperature known as the freezing point, the particles won’t have enough energy to overcome the forces of attraction, coming together and forming a solid.
Factors affecting rate of evaporation?
- Temperature
- Are of the exposed surface (The higher the exposed area the more opportunities for the particles to escape).
- Humidity of the surrounding air (The higher the humidity is the slower the evaporation).
- Motion of air (Replaces the humid air with dry air)
- Pressure (The lower the external pressure, the higher the evaporation rate as it is pushed on less).
- Nature of liquids
How does evaporation help in cooling?
When the hotter, faster particles escape, the slower and colder molecules are left behind, lowering temperature.
Boiling compared to Evaporation?
- Boiling only happens at 100 degrees
- Boiling happens throughout the liquid but evaporation only at the surface.
- A boiling liquid always bubbles but evaporation can happen without bubbling
- In boiling the kinetic energy of the particles must be increased but in evaporation, only the most energetic particles escape
Define specific heat of fusion
The energy required per kg to change the substance from solid to liquid at its melting point
Define specific heat of vaporisation
The energy required per kg to change the substance from liquid to gas at its boiling point
