156 SCIENCE OF HOME AND COMMUNITY 



Then rub the other end of the needle on the other end of the 

 magnet. See if the needle will pick up tacks. The blade of a 

 jackknife may be magnetized by rubbing over a magnet. Try 

 bringing another needle near a pole of a magnet, but not quite 

 touching it. See if the needle becomes magnetized. 



B. The Electromagnet 



Apparatus. Large nail or bolt about six inches long, about 

 twenty feet of insulated wire, two dry cells, tacks, magnet. 



Directions, i. An electromagnet is an important part of an 

 electric bell. It can be made as follows. Wind about ten 

 feet of insulated wire around a large nail or bolt as thread is 

 wound on a spool. Place the end of the nail in a pile of tacks. 

 Is it a magnet? Connect the wire with a dry cell. Is it a 

 magnet now? Withdraw the nail and see whether the coil 

 will pick up fewer or more tacks. Disconnect the cell. What 

 happens ? Connect the cell again. See if a needle can be mag- 

 netized by rubbing against the nail. 



2. Wind five feet of wire around the nail and see how the 

 number of tacks it lifts up compares with the number when 

 ten feet of wire were used. Try twenty feet and note the dif- 

 ference. Try two cells and compare with the number of tacks 

 lifted when one cell was used with the same length of wire. In 

 what ways do these experiments show that the strength of an 

 electromagnet may be increased ? 



C. The Electric Bell 



Apparatus. Electric bell, push button, cell. 



Directions. Connect the bell and push button with the cell. 

 Push on the button and notice what parts of the bell move. 

 Make a drawing showing the connections of the bell, button, 

 and cell. Make a careful drawing of the bell. By means of 

 arrows show through what parts of the bell the current passes. 



Cells. A very simple cell may be made by putting strips 

 of copper and zinc, with a wire attached to each, into a weak 

 solution of sulfuric acid. If the wires are brought together, 



