Physics- Thermal Insulation Flashcards
(15 cards)
Describe how the design of a vacuum flask keeps the liquid inside hot.
-The Vacuum between the two glass walls prevent conduction and convection through the sides
-The Silvered surfaces minimise heat transfer by Radiation as its reflected back towards the hot liquid and is a poor emitter of radiation so less heat is lost to the surroundings
-The Plastic Cap minimises conduction and convection through the top of the flask as it’s a poor conductor of heat
-The Sealed design prevents the entry of air, which may affect the liquid’s temperature, so heat cannot escape, and the liquid retains it’s warmth
Name three reasons why insulators are useful:
-To prevent heat loss, therefore reducing energy bills
-To prevent injuries
-To keep something hot or cold
How do Insulators prevent heat loss and name two excellent insulators:
Insulators prevent heat loss by reducing (or stopping) the amount of conduction, convection or radiation.
Air is an excellent insulator- trapping air prevents conduction and if the air cannot flow, convection cannot take place so a vacuum prevents these both.
Shiny surfaces can reflect radiant heat back to where it’s required.
Why is insulating your home important?
Give two reasons.
Insulating your home is important to ensure that you stay warm in the winter months. If less heat can escape to your surroundings, you aren’t wasting energy , therefore reducing your impact on the environment and saving money on energy bills.
What is the formula for calculating payback time?
The payback time of an insulation method is the length of time to recover the cost of insulation based on the annual savings on the energy bill.
PAYBACK TIME = INITIAL COST / ANNUAL SAVINGS
What is the formula for calculating profitability?
You can determine how much profit you would make over a given period of time. This is useful for determining which method would be the best long term investment.
PROFIT = (ANNUAL SAVING x TIME) - INITIAL COST
Describe three Home Insulation Methods:
-A significant amount of heat loss happens through the roof.
FIBREGLASS LOFT INSULATION is made of many fibres, trapping air and preventing heat loss by conduction and convection at the top of the house
-CAVITY WALLS are double-layer walls with an air gap in between, preventing conduction. The cavity may be filled with fibreglass, foam, polystyrene, to prevent conduction.
-DOUBLE (OR TRIPLE) GLAZED WINDOWS are panes of glass separated with a narrow air gap- vacuum. This prevents conduction and convection.
List three benefits of replacing your windows with glazed ones?
-Sound proofing which is useful if you live near a busy road
-Stronger windows which is better for security
-Therefore, they can increase the value of your home.
What about some less expensive insulation methods?
-An insulated jacket around the hot water tank
-Placing reflective foil behind radiators
-Using carpets with underlay, rather than wooden floors
What is the U-value?
The U-value is the amount of energy that passes through the wall each second. The lower the U-value, the less energy passes through the material, therefore the more effective the insulator is.
Write the method for the Required Practical- Thermal Insulation.
Safety warning-Ensure that you are aware of the risks of hot water, spillages and broken glass.
-Take three 250cm cubed beakers: wrap one in one layer of insulation, wrap the second beaker with two layers of insulation and leave the third beaker uncovered (as a control experiment).
-Pour 100cm cubed boiling water into each beaker; cover the beaker with a lid and record the initial temperature of the water, using a thermometer in a small hole in the lid (which may also be insulated).
-Immediately start the timer. Record the temperature of the water in each tube at one-minute intervals for a total of 15 minutes.
-If time allows, you could repeat the experiment using other combinations of materials.
How would you write the results of this required practical?
-Draw a results table with four columns- one showing time (in minutes), and then one column for each of the beakers, showing the temperature of the water (in degree celsius).
-Plot a graph, showing temperature (y-axis), against time (x-axis). Plot the data for each beaker on the same axes, connecting the points with a smooth curve of best fit- you will have three curves on each graph- don’t forget to label them.
What is the difference between random and systematic errors?
Random errors are errors made by the person carrying out the measuring, and are usually down to timing incorrectly, or reading the instrument incorrectly. While, systematic errors are errors which cause the results to differ from the true value by a consistent amount each time.
What are some things that must be ensured in this Thermal Insulation practical?
-That the initial results are NOT recorded before the thermometer has reached it’s peak
-That all the timers start at the same time
-That all the beakers are at the same temperature
-That the water is all poured in at the same time
What is a parallax error?
Parallax error is caused by a student not reading the measurement at eye level. It can lead to the reading being too high or too low.
