ELECTRICITY IN THE HOME 155 



LABORATORY EXERCISE 18 



Purpose. To study the working of an electric bell. 



An electromagnet is an important part of the electric bell, 

 so in order to understand how this works we will first study 

 magnets. 



A. The Magnet 



Apparatus. Two bar magnets, horseshoe magnet, pieces of 

 metal, such as iron, steel, tin, zinc, a dime, a copper, a nickel, 

 piece of glass, iron filings, darning needle, blue-print paper. 



Directions, a. Magnetic substances, i. Take a magnet and 

 try a great many substances to see which it will attract. Find 

 the greatest distance that a piece of iron is attracted. Put 

 the end of the magnet in a box of tacks. By trying various 

 portions of the magnet see which is the strongest part. Put 

 the magnet in iron filings. 



2. Test needles, pins, pens, etc., to see if they are made of 

 iron or steel. 



b. The magnetic field. I. Place a bar magnet on the table 

 and put over it a sheet of paper. Sprinkle iron filings over this 

 paper. Make a drawing showing the way the filings arrange 

 themselves. Put two like poles of two bar magnets about an 

 inch apart. Over these put a piece of paper and on it sprinkle 

 the iron filings. Draw. Do the same with two unlike poles. 

 Draw. What is the difference in the arrangement of the 

 filings ? Place a horseshoe magnet under the paper and sprinkle 

 the filings. 



2. To make blue prints of the magnetic field. Repeat the 

 previous experiments, only instead of the ordinary paper, use 

 a piece of blue-print paper over the magnets. Place in a shaded 

 part of the room and sprinkle filings on the paper. Carefully 

 place a piece of glass on the filings and put magnet and all in 

 the sunlight and allow to stand till the paper becomes bronze. 

 This will take from five to twenty minutes, according to the 

 light. Then shake off the filings and wash the paper in several 

 changes of water and then dry. 



c. How to make magnets. Rub one end of a needle on one 

 end of a magnet, rubbing several times in the same direction. 



