ELEMENTARY THEORY OF MAGNETISM. 17 



north pole of 600 units strength at Washington. Ans. 1.07 

 gausses, north, and dipping 28 36' below the horizontal. 



11. One of the magnets specified in problem I is balanced 

 horizontally on a knife edge at Washington. The magnet weighs 

 1 20 grams. Find the horizontal distance from the knife edge 

 to the center of the bar. Use the data specified in Problem 9. 

 Ans. 0.046 centimeter. 



12. The moment of inertia of one of the magnets specified in 

 problem I is 9,000 gr.-cm. 2 . Calculate the time of one complete 

 oscillation of this magnet when it is suspended horizontally at 

 Washington. Ans. 11.15 seconds. 



13. A magnet makes one complete oscillation per second in a 

 magnetic field of which the intensity is 0.2 gauss. Another 

 magnet is twice as long, twice as wide, and twice as thick, it is 

 magnetized to twice the intensity (units pole per unit sectional 

 area) and it is suspended in a field of which the intensity is O.I 

 gauss. What is its period of oscillation? Ans. 2 seconds. 



Note. The moment of inertia of a rotating body is equal to the product of the 

 mass of the body into the square of its radius of gyration. Given two bodies of 

 exactly the same shape, their radii of gyration are proportional to their linear 

 dimensions, whereas their masses are proportional to their volumes. 



14. A suspended magnet makes 20 oscillations in 184.5 seconds 

 at one place, and 20 oscillations in 215.8 seconds at another place. 

 What is the ratio of the intensities of the horizontal component of 

 the earth's magnetic field at the two places, and at which place 

 is it the more intense? Ans. 1.367. Field more intense at first 

 place. 



