2. Read one more text on the problem and do the tasks. Heat Conductivity

A. The ability of any material to conduct heat depends on its specific conductivity and its specific heat, i.e. the amount of heat required to raise unit weight (1gm) of its substance 1C. Though the specific heat of wood substance is similar to that of many metals, or even greater, the conductivity is very much less because all dry woods contain a considerable volume of air enclosed in the cells. The conductivity of green unseasoned timber is much higher than that of dry wood as in green wood the cells are filled with water which is a better conductor of heat than air is.

B. The conductivity of dry wood depends greatly on its density; the lighter the wood the better are its insulating properties. Balsa wood was used as an insulating material long before the invention of expanded plastics.

3. The excellent insulating properties of timber make it a particularly suitable material for walls of buildings in cold climates. The traditional cottages in Russia were built of solid logs. Panelling a room with wood not only greatly reduces the heat loss through the walls but it also enables the room to be heated more quickly. Because wood conducts heat so poorly it is the ideal material from which to make such things as saucepan handles, and for the same reason silver teapots are often made with an insert of ebony between the pot and the handle so that the latter does not become uncomfortably hot to hold.

D. The slow conduction of heat through timber renders it suitable (rather surprisingly at first thought) for the construction of fire-resistant doors. Provided that the panels do not separate and so do not make openings through which flames can pass, a well-made, solid timber door can resist the penetration of fire for a long time. For the same reason large timber beams may continue to support a building long after unprotected steel joists have collapsed due to softening of the metal by heat. Similarly, papers in a metal filing cabinet are more likely to be charred than those in a wooden one during a fire of fairly short duration.

Task 1.

Define which of the statements are:

A - true B- false C - not mentioned in the text

1. Heat conductivity of wood depends on the state of dryness of wood.

2. As heat conductivity of wood is low it is not used as a building material.

3. Wooden doors do not resist to the penetration of a fire.

4. Heat conductivity of wood depends on the strength properties of wood.

Task 2.

Which paragraphs (A ,B, C, D) express the following ideas.

1. Low heat conductivity of timber helps to keep our homes warm.

2. Dry wood possesses low heat conductivity because of air filling the cell cavities.

Task 3.

Answer the question. Make the right choice.

What must be done to prevent the passage of heat to the teapot handle?

A. It must be made of gold.

B. It must have a high quality finishing.

C. A piece of wood must be inserted into the handle.

D. It must be made of green wood.

Task 4.

Finish the sentence in accordance with the text.

The conductivity of dry wood is very much less because of _____.

A. air enclosed in the cells

B. moisture

C. knots

D. fungi

Task 5.

Define the main idea of the text.

A. Heat conductivity of wood does not affect its use.

B. Heat conductivity of wood is of no value for its utilization.

C. Heat conductivity makes wood suitable for a wide variety of applications.

D. Heat conductivity is very important for fire fighting.

Task 6.

Who is this text of great interest to?

It is of great interest to _____ .

A. drivers

B. computer programmers

C. engineers of wooden construction

D. doctors