Thermal Physics Flashcards
What is conduction
Vibrating molecules (solids)
What is convection
Vibrating molecules (liquid or gas)
What is radiation
Waves from the electromagnetic spectrum, especially involving IR
What reduces conduction
An insulator
What reduces convection
Trapping the liquid or gas in small pockets
What reduces radiation (2)
- Shiny, light coloured surfaces
- Low surface temperature
What stops conduction (2)
- A vacuum
- A layer of gas
What stops convection
A vacuum
What stops radiation
Nothing
Are gases very good insulators or conductors and why
Poor conductors, very good insulators, because the molecules are far apart
What is the definition of specific heat capacity
The amount of energy required to heat a substance by 1ºC per unit mass
What are the units for specific heat capacity
Joules per kilogram per ºC (J/KG/ºC)
What is the equation for specific heat capacity energy
Energy = mass x specific heat capacity x change in temperature
q = mc∆T
Why do we get different results for the SHC of water when we do an experiment compared to the actual value
The experiment is unreliable - not 100% efficient, some heat lost to surroundings
What is the specific heat capacity of water
4200 J/KG/ºC
What is internal energy
The sum of all the kinetic and potential energies of the particles in a substance
What happens to the energy of an object if the temperature increases/decreases
Increases = more energy
Decreases = less energy
What increases when kinetic energy increases
Velocity
What is the link between the average kinetic energy of particles in a substance and the temperature of the particles
Directly proportional
Define temperature using energy
Temperature is a measure of the average kinetic energy of molecules in a substance.
Describe the solid state (3)
Solids are very compact and vibrate back and forth. Held in place by stronger intermolecular forces than in liquids.
Describe the liquid state (3)
Shape/volume as a hint
Liquids move to fill a container but they slide over each other. Takes the shape of a container but not the volume.
Describe the gas state
Shape and volume as a hint
Gases are very spaced out and are free to move. They take the shape and volume of the container that they are in.
What is a fluid
A liquid or a gas
What is the change of state from gas to solid or solid to gas called
Sublimation
Name a substance that can sublimate
Dry ice (CO2)
Do these have a set volume or changeable
Gas
Liquid
Solid
Gas = changeable
Liquid = fixed
Solid = fixed
Do these have fixed or changeable shape
Gas
Liquid
Solid
Gas = changeable
Liquid = changeable
Solid = fixed
How do particles move as a gas
Freely and quickly
How do particles move as a liquid
Fluid motion
How do particles move in solids
Particles vibrate around fixed positions
What is the change of state from gas to liquid called
Condensation
Are feathers and fur good or bad insulators
Good
Why are cooling units at the top of a freezer, but the heating element in a water tank is at the bottom
Heat rises
Why is it more comfortable to wear white than black in summer
Bright colours reflect energy from the sun, but black absorbs it
Why do people with hypothermia get wrapped in a plastic sheet coated with shiny aluminum
Plastic insulates, foil is shiny so keeps heat in and keeps cold out
Why are several layers of thin clothes better at keeping you warm than one thick layer
Air is a good insulator and there are layers of air between the thin clothes layers
Why is newspaper used to keep fish and chips hot but ice cream cold
It is a bad conductor/a good insualtor
Why is a fire fighting suit bright and shiny
To reflect the heat of the fire away from the person
Why is the inside of a greenhouse warmer than the outside
Glass allows heat in but then traps it inside
Why does food in a chest freezer stay frozen for long when the door is open but in an upright freezer it will being to defrost quickly
Heat rises
Why does your face go vividly red during exercise
The body tries to lose heat by sending the blood closer to the skin to lose some heat to the surroundings
How do you calculate specific heat capacity from a graph of Energy transferred (x) and temperature (y)
C = 1/gradient x mass
How do you calculate specific heat capacity
ΔE = mc Δ ϴ
Change in energy = mass x specific heat capacity x change in temperature
This reaction is also known as Q = mc ΔT
Describe an experiment a student can carry out to measure the specific heat capacity of a metal block. (6 marks)
To determine the specific heat capacity of a metal block, the following equipment would be required: a power supply, wires, a metal block, a thermometer, an ammeter, a heating rod, a voltmeter and an insulating layer of wool to surround the metal block.
1. Set up the circuit, with the heating rod and thermometer in separate holes in the metal block, but with the power off.
2. Record the initial temperature of the block.
3. Turn the power on and read the ammeter and voltmeter to get the readings for voltage and current.
4. Every 30 seconds, measure the current, voltage and temperature of the metal block and record in a table. Repeat for 10 minutes.
5. Use voltage x current to work out the power, then multiply by the time to work out the total output of energy from the system, working this out for every 30 second interval.
6. Plot a graph of energy transferred on the X-axis and temperature on the Y-axis.
7. Find the gradient.
8. Calculate the specific heat capacity using the equation c = 1/(mass x gradient).
9. Repeat the experiment 2 more times.
10. Calculate the average results from these repeats.
