The R-Value of an Insulating Material Is the Thickness of the Material

question 19

Multiple Choice

The R-value of an insulating material is the thickness of the material divided by its thermal conductivity. When an insulating material consists of three layers with R-values R1, R2 and R3, the overall R-value of the insulation is given by:

• A)R = R1 + R2 + R3.
• B) \(R=\frac{R_{1} R_{2}+R_{1} R_{3}+R_{2} R_{3}}{R_{1}+R_{2}+R_{3}}\) .
• C) \(R=\frac{R_{1} R_{2} R_{3}}{R_{1} R_{2}+R_{1} R_{3}+R_{2} R_{3}}\) .
• D) \(\frac{1}{R}=\frac{1}{R_{1}+R_{2}+R_{3}}\) .
• E) \(\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}\) .

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Definitions:

Power Transmission Wire

Conductors used in power transmission systems to carry electricity over long distances from power plants to electrical substations.

Domestic Demand

The total demand for goods and services within a country's borders.

Foreign Demand

The desire and willingness of buyers in other countries to purchase goods and services from a particular country.

Consumer Surplus

The difference in the total funds consumers are prepared to allocate for a good or service against the total funds they genuinely allocate.