P2 Energy Transfer by Heating Flashcards
What is a conductor?
A conductor is a material that allows
internal (thermal) energy
to be transmitted through it easily.
Why are metals good conductors?
All metals are good conductors. When one end of a metal rod is put into a fire, the energy from the flame makes the
ions in the rod vibrate faster. Since the ions in the solid metal are close together, this increased
vibration means that they collide with neighbouring ions more frequently. Energy is passed on through the metal by these collisions, transmitting the energy. More frequent collisions increase the
rate of transfer.
What is an insulator?
Material that does not allow charge or heat to pass through it easily.
why is it better to have a window made of two layers of glass with a layer of air trapped between them?
Both glass and air are insulators because they have low thermal conductivities. The layer of air has the lowest thermal conductivity and reduces the overall conductivity of the window unit. Since air and glass are both transparent people can still see through the window.
Insulation material Required practical:
https://www.youtube.com/watch?v=MUy1o4ogCvw&list=PLAd0MSIZBSsGNWKdHJdQYIndKl3HZUrSB
Place a small beaker into a larger beaker.
Fill the small beaker with hot water from a kettle.
Put a piece of cardboard over the beakers as a lid. The lid should have a hole suitable for a thermometer.
Place a thermometer into the smaller beaker through the hole.
Record the temperature of the water in the small beaker and start the stopwatch.
Record the temperature of the water every 2 minutes for 20 minutes.
Repeat steps 1-6, each time packing the space between the large beaker and small beaker with the chosen insulating material.
Plot a graph of temperature (y-axis) against time (x-axis).
This graph shows:
The curve which takes the longest time for the water temperature to drop (the shallowest) should be the material which is the best insulator.
The temperature falls quickly at high temperatures and slowly at low temperatures.
When the beaker is at a high temperature, there is a big difference between the temperature of the beaker and the temperature of the surrounding air. This means there is a high
rate
of transfer.
When the beaker is at a lower temperature, there is less difference between the temperature of the beaker and the temperature of the surrounding air. This means there is a lower rate of transfer.
Insulation thickness required practical:
Method
Wrap a sheet of newspaper around a 100 ml beaker.
Fill the beaker with hot water from a kettle.
Put a piece of cardboard over the beaker as a lid. The lid should have a hole suitable for a thermometer.
Place a thermometer into the beaker through the hole.
Record the temperature of the water in the beaker and start the stopwatch.
Record the temperature of the water every 2 minutes for 20 minutes.
Repeat steps 1-6, each time adding another layer of newspaper around the beaker until there are 10 layers of newspaper wrapped around the beaker.
Plot graphs of temperature against time.
All objects emit_____
All bodies (objects) emit and absorb
infrared radiation
. They do this whatever their
temperature
. The hotter the body:
the more infrared radiation it gives out in a given time
the greater the proportion of emitted radiation is visible light
What is a black body ?
A perfect black body is a
theoretical object. It would have these properties:
it would absorb all the radiation that falls on it
it would not
reflect or transmit any radiation
An object that is good at absorbing radiation is also a good emitter, so a perfect black body would be the best possible emitter of radiation.
What are poor emitters?
A perfect black body is a
theoretical object. It would have these properties:
it would absorb all the radiation that falls on it
it would not reflect or transmit any radiation
An object that is good at absorbing radiation is also a good emitter, so a perfect black body would be the best possible emitter of radiation.
Infrared required practical:
https://www.youtube.com/watch?v=LFwio38EK9s&list=PLAd0MSIZBSsGNWKdHJdQYIndKl3HZUrSB&index=2
Aim: To investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
Method:
Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid.
Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water.
Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.
What are the factors for change in temperature?
Different materials require different amounts of energy to change temperature. The amount of energy needed depends on:
the mass of the material
the substance of the material (specific heat capacity)
the desired temperature change
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1 kg of substance by 1°C.
Measured in J/kg/°C
Measuring specific heat capacity Required Practical:
Aim of the experiment
To measure the specific heat capacity of a sample of material.
Method
Place the immersion heater into the central hole at the top of the block.
Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by hot material.
Fully insulate the block by wrapping it loosely with cotton wool.
Record the temperature of the block.
Connect the heater to the power supply and turn it off after ten minutes.
After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.
What is the formula for energy transferred in specific heat capacity?
energy transferred,ΔE(joules,J)=mass,m x specific heat capacity,c x temperature change, Δθ
How to insulate homes?
Trapped air is a natural insulator and because it is trapped, convection currents cannot be set up easily. So, trapped air reduces heat loss by conduction and convection. Many insulating materials incorporate trapped air.
There are several different ways to reduce heat loss:
Simple ways to reduce heat loss include fitting carpets, curtains and draught excluders. It is even possible to fit reflective foil behind radiators.
Heat loss through windows can be reduced by using double glazing. These windows have dry, trapped air between two panes of glass. This reduces heat loss by conduction and convection. Air is a poor
conductor
and by trapping it between the panes, convection currents cannot be set up.
Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall. Insulating materials are bad conductors and so this reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.
Heat loss through the roof can be reduced by laying loft insulation. Air is trapped between the fibres of the insulation, reducing heat loss by conduction.
