The Propagation of Heat 199 



QUESTIONS 



1. Suggest a simple method of determining experimentally 

 which of two spoons is made of silver and which of electro-plate. 



2. Good radiators are good absorbers of heat. Describe an 

 experiment in illustration of this statement. 



3. Good reflectors of heat are bad absorbers. By what experi- 

 ments would you try to show that this statement is correct ? 



4. Pieces of black and white cloth are spread out on the surface 

 of snow in bright sunlight. The snow underneath the black cloth 

 is observed to melt more quickly than that under the white. How 

 do you account for this ? 



5. Why are blankets used to keep the body warm in winter 

 and to prevent the melting of ice in summer ? 



6. Pieces of wood or ivory are often inserted between the 

 handle of a tea-pot and the pot itself. What is the reason of this ? 



7. Why does the presence of a chimney assist a fire to burn 

 more steadily and brightly than it does when no flue is provided ? 



8. Why does the door-knob feel colder than the door, and the 

 door colder than the carpet ? 



9. A Norwegian cooking-box consists of a large box thickly 

 lined with straw or felt, provided with a lid similarly lined. Cooking- 

 vessels placed in the interior of the closed box remain warm for some 

 hours. Give reasons for this. 



10. A sheet of brown paper and a powerful magnifying glass 

 are placed under the receiver of an air-pump in such positions that 

 the paper is at the focus of the lens. The air is then exhausted 

 from the receiver as completely as possible, and the whole apparatus 

 placed in bright sunlight so that the lens faces the sun. Will the 

 paper be burnt ? Give arguments in support of your opinion 



