PART II 



CHAPTER I 

 INDUCTANCE AND INDUCED E.M.F. 



1. A current of 25 amperes changes in T \j of a second to 5 

 amperes; required the rate of change of the current during this 

 time. (^ min.) 



2. When five amperes flow^ through a circuit surrounding an 

 iron ring, there is a flux of 10 5 maxwells; when the current is 

 increased to 10 amperes, the flux increases to 1.6 X 10*. Required 

 the average rate of change of flux with current within the above 

 current limits. (^ min.) 



3. During the first 10 minutes a man goes 1J miles, during the 

 next 20 minutes he goes 2 miles and in the next half hour he goes 

 H miles. What are his average speeds, or rates of change of dis- 

 tance with time, during the first 30 minutes and during the whole 

 time? Assuming a regular decreasing speed, what is his instan- 

 taneous speed at the end of 20 minutes? (/ min.) 



4. At a certain point in a city property sells for $120 per front 

 foot. Half a mile farther out its value has dropped to $80, at 1 mile 

 it is $60, at 2 miles it is $30 and at 3 miles $20. Find the average 

 rate of change of value with distance within the above limits. 

 Find also the rate (instantaneous) at which values are changing 

 at the 2-mile point. (5 min.) 



5. A ring is built of wrought-iron rod, having an area of 20 

 sq. cm. The mean diameter is 25 cm. and there are 2000 turns 

 in the winding. Required the average rates of change of flux 

 density and total flux, with current, when the exciting current is 

 brought from zero to values of 0.25, 1, 3 and 5 amperes respectively. 

 Use the curve for wrought iron given on page 105. (15 min.) 



6. In the case of problem 5, find the instantaneous rate of 

 change of flux, when the current is passing through a value of one 

 ampere. Also find the , average rate between one and three 

 amperes. (5 min.) 



7. A conductor in the form of a loop is threaded by 10* lines of 



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