5. a) (2) Define density ; specific gravity. 



b) (8) When a meter stick is made to float upright in pure water, 18.5 cm. 

 of the stick projects above the water and when similarly floated 

 in a second liquid, 24 cm. of the stick projects above. What are 

 the specific gravities of the second liquid and the meter stick ? 



Group II 



6. a) (6) A 50-ft. steel tape is correct at 20° C. How long would it be at a 



temperature of — 10° C. ? (Coefficient of linear expansion of steel 

 =0.000012.) 

 b) (4) Describe two instances where the change of size of a solid with change 

 of temperature is of practical use; and two instances where the 

 change of size is not desired but has to be allowed for. 



7. a) (4) Why does a person feel more comfortable on a hot dry day than on 



a humid day of the same temperature ? 

 b) (6) 100 gm. of a liquid whose specific heat is 0.6 and temperature 80° C. 

 are mbced with 300 gm. of water at 15° C. What will be the 

 temperature of the mixture ? Assume the interchange of heat to 

 be confined to the two liquids. 



8. a) (3) What is the essential feature in the construction of a " fireless cooker " ? 



b) (2) Is the cooking done entirely without a source of heat ? 



c) (2) Explain wherein its use is economical of heat. 



d) (3) What is meant by conduction of heat; by convection; by radiation? 



Group III 



9. a) (3) What do the terms "frequency" and "wave-length" mean, as used 



in the study of sound ? 



b) (4) If low C has a frequency of 128, what is the frequency and wave- 



length at 0° C. of the note one octave higher ? 



c) (3) State and explain the effect on the pitch of increasing the speed of a 



phonograph. 



Group IV 



10. a) (2) State the law of reflection of light, making use of a diagram. 



b) (5) A plane or convex mirror is often placed on an automobile to allow 



the driver to see in it the reflection of what is in the rear. What are 

 the advantages of the convex mirror; of the plane ? 



c) (3) Why is not a concave mirror, which may form a magnified image, 



better than either of the others for the purpose ? 



11. a) (4) Describe in detail a laboratory method of determining the index of 



refraction of glass or of water. 



b) (4) What measurements must be made and how is the index computed 



from them ? 



c) (2) What is the velocity of light through water ? (Index of refraction of 



water =1.33.) 



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