When the bell does ring, watch it very carefully for 

 a few seconds in order to determine what part of it is 

 in motion. 



Make a careful drawing of the mechanism of the bell, 

 and explain fully where motion occurs and why. 



When your home door bell fails to ring, what do you 

 think may be one trouble ? 



EXPERIMENT 88. MAGNETS AND THEIR ACTION ON IRON 



FILINGS 



1. Lay a strong bar-shaped magnet on iron filings; 

 then remove and sketch the appearance of the bar. 



The places at which the filings adhere in greatest number 

 are called poles. How many poles does the bar magnet 

 have ? 



2. Lay the magnet on the table, put a sheet of paper 

 over it, and lightly sprinkle iron filings on the paper. Tap 

 the paper gently. Do the filings assume any definite ar- 

 rangement ? If so, sketch the appearance roughly. 



Repeat the experiment, using a thin piece of glass in- 

 stead of paper. Is the arrangement of the filings the 

 same as before ? 



What do we call the lines along which the filings arrange 

 themselves ? 



3. Lay a horseshoe-shaped magnet on filings ; remove, 

 and sketch the appearance. How many poles does this 

 magnet have ? Using the horseshoe magnet, repeat the 

 experiment which shows the existence of lines of force, 

 sketching the appearance as before. 



