IGCSE Thermal Physics Flashcards
Define Pressure
Pressure is the force per unit area.
Why does a sharp knife cut better than a blunt knife?
A sharp knife has a smaller area than a blunt knife
PRESSURE = FORCE ÷ AREA
The same FORCE over a smaller AREA will result in a greater PRESSURE.
Describe the arrangement and motion of particles in a solid.
Particles vibrate about fixed positions with a close-packed regular structure
Describe the arrangement and motion of particles in a liquid.
Particles move with a random motion and slide over each other, moving around freely.
Liquids have a close-packed irregular structure.
Describe the arrangement and motion of particles in a gas.
Particles are spread out and move around freely with a rapid random motion.
Why is there a pressure on the walls of a container of gas?
Particles collide with the walls of the container exerting a force on the surface area of the container
PRESSURE = FORCE ÷ AREA
There are a large number of particles colliding and therefore a significant force and pressure.
What happens when a gas is heated?
As the temperature increases
• the KINETIC ENERGY (and SPEED) of the particles increases
• the particles collide more frequently with the walls
• hitting the walls harder (with more force)
• so the PRESSURE increases.
What is the difference between Evaporation and Boiling?
EVAPORATION:
• Molecules with sufficient kinetic energy leave the SURFACE of the liquid.
• Kinetic energy of the remaining molecules decreases so the liquid cools.
• Occurs below the boiling point.
BOILING:
• Occurs THROUGHOUT a liquid at a FIXED TEMPERATURE.
• Bubbling occurs.
State 3 factors that will increase the rate of evaporation.
Increased Temperature
Increased Surface Area
Draught across the surface
What happens to the pressure if a volume of a gas is reduced?
If the volume is reduced the particles will collide with the container walls more frequently so the pressure increases.
Which expands more, solids, liquids or gases?
Gases expand the most, Solids the least.
Define Thermal Capacity
The energy that must be supplied to an object to raise its temperature by 1°C
Define Specific Heat Capacity
The energy needed to raise 1kg of a substance by 1°C.
What is Latent Heat Energy?
The energy used or released when a substance changes its temperature with out changing its temperature.
Define Specific Latent Heat?
Specific latent heat of fusion is the energy needed to melt 1kg of the substance without change of temperature.
Specific latent heat of vaporisation is the energy needed to boil 1kg of the substance without change of temperature.
