College Physics with MasteringPhysics 7th Edition by Jerry Wilson,Anthony Buffa,Bo Lou

Exercise 69

A piece of pine 14 in. thick has an R-value of 19. For glass wool to have the same R-value, its thickness should be (a) thicker than, (2) the same as, (3) thinner than 14 in. Why (b) Calculate the required thickness of such a piece of glass wool. (See Exercise and Insight 11.2.)
Exercise
The thermal insulation used in building is commonly rated in terms of its R-value , defined as d/k , where d is the thickness of the insulation in inches and k is its thermal conductivity. (See Insight 11.2 on p. 403.) In the United States, R-values are expressed in British units. For example, 3.0 in. of foam plastic would have an R-value of 3.0/0.30 = 10, where k = 0.30 Btu · in./(ft 2 · h · °F). This value is expressed as R-10. (a) Better insulation has a (1) high, (2) low, or (3) zero R-value. Explain. (b) What thicknesses of (1) styrofoam and (2) brick would give an R-value of R-10