Lesson 2.7 - Check Your Understanding

Before you start the assignment, answer all the Check Your Understanding questions on page 119 in your textbook.

 

 

Answers to Check Your Understanding questions:

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. a.  The R-value of 25 mm of airspace = 2.04.  The R-value of 25 mm of expanded polystyrene = 3.96.  Therefore, the sum for both types of insulation is 2.04 + 3.96 = 6.00.
b.  The R-value of 25 mm of rigid urethane foam = 7.50.  The R-value of 25 mm of solid wood = 1.25.  Therefore, the sum for both types of insulation is 7.50 + 1.25 = 8.75.
c.  The R-value of 25 mm of airspace = 2.04.  The R-value of 25 mm of concrete = 0.19.  Therefore, the sum for both types of insulation is 2.04 + 0.19 = 2.23.

Question 2. Pockets of air are trapped among the shavings.  This reduces heat transfer by conduction.

Question 3. Walls are limited to small thicknesses.  Imagine what your house would look like if the walls were 75 cm thick.  Builders can put limited amounts of insulation in the walls.  The attic is different. Builders can put very thick insulation in the attic; the height of the roof is the limit.

Question 4. Aluminum foil has a shiny side that reduces heat transfer by radiation.

Question 5. a.  Windows are made of glass, which is a poor insulator.  Doors are quite thin so a door is more difficult to insulate than a thicker wall.  Also, windows and doors must open, and the cracks around them are difficult to seal.
b.  Heat transfer through doors can be reduced by filling the hollow door with high insulation urethane foam and by installing good weather-stripping seals around the door and frame.  Windows can have double or triple glazing, argon gas filling, specially coated surfaces, and good weather-stripping and caulking.

Question 6. Non-metals are usually good insulators and will not get as hot as metal handles do.  The handles must not burn your hands when you pick up the pot or pan.

 


Now, do Assignment 6B.  Page forward to access the computer-scored assignment.