Thermal physics Flashcards
What are 2 distinguishing properties of solids?
- Have a definite shape
2. Have a definite volume
What are 2 distinguishing properties of liquids?
- Have no definite shape
2. Have a definite volume
What are 2 distinguishing properties of gases?
- Have no definite shape
2. Have no definite volume
Describe the molecular structure of solids
- Strong forces of attraction between particles
- Regular pattern
- Very close together
- Vibrate about fixed positions
Describe the molecular structure of liquids
- Weaker forces of attraction between particles
- No regular pattern
- Close together
- Slide past each other
Describe the molecular structure of gases
- Very weak forces of attraction between particles
- No pattern
- Widely separated
- Move randomly at high speeds
What is the effect of an increase in temperature of a gas?
The hotter the gas, the faster the molecules move
What causes pressure on the walls of a container?
- Collision of molecules with the walls of a container
2. Collision applies a force across the surface area of the walls
Explain pressure
Change of momentum of the particles striking the walls creating a force
What is Brownian motion?
Random molecular bombardment of small particles
What causes Brownian motion?
Molecules in a gas/liquid colliding at high speeds with small particles
Describe evaporation
The escape of more-energetic molecules from the surface of a liquid
What is the effect of evaporation?
Cooling of the liquid
What are 3 factors that influence evaporation?
- Surface area
- Temperature
- Draught
How does surface area affect evaporation?
A greater surface area results in more area for particles to escape the liquid
How does temperature affect evaporation?
High temperatures give particles more energy to escape from the surface of the liquid
How does draught affect evaporation?
If the air is less humid, fewer particles are condensing
Why does evaporation result in the cooling of a liquid?
- Average energy of remaining molecules decreases
2. Temperature of the liquid also decreases
What happens to a body in contact with an evaporating liquid?
It cools
State Boyle’s Law
For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume
Describe thermal expansion of solids at constant pressure
Expand slightly
Why do solids expand slightly?
Due to strong bonds holding molecules together
Describe thermal expansion of liquids at constant pressure
Expand more than solids
Why do liquids expand more than solids?
Due to weaker bonds between molecules
Describe thermal expansion of gases at constant pressure
Expand significantly
Why gases expand significantly?
Very weak bonds between molecules
Give 2 examples of properties that change when a substance is heated
- Volume (and density)
2. Electrical resistance
What is a fixed point?
A temperature at which some easily identifiable change occurs
What are the 2 fixed points used in a thermometer?
Lower point and upper point
What is usually used as the lower point?
0 °C
What is usually used as the upper point?
100 °C
What is the need for fixed points?
To know the temperature without having to measure it directly?
What does a liquid-in-glass thermometer consist of?
- Thin glass capillary tube
- A liquid that expands with temperature
- A glass bulb
- A scale
What is sensitivity?
The ability to detect small changes in temperature?
What 3 factors increase sensitivity?
- Use a smaller glass bulb
- Use a narrower tube
- Use a thinner wall
How does using a smaller glass bulb increase sensitivity?
It contains less liquid so absorbs more heat in a less time
How does using a narrower tube increase sensitivity?
A small change in volume results in the liquid moving a larger distance along the tube