HOW ELECTRICITY IS GENERATED 



249 



(Show with an arrow.) When the coil was not moving over 



the magnet the galvanometer needle When the coil 



was removed from the magnet pole the galvanometer needle 

 moved (Show with an arrow). When the magnet was 



FIG. 391 



moved in and out of the coil, flowed in the coil and 



galvanometer. A current is generated in the coil whenever 

 are cut by 



Experiment 154. How does the magneto of a tele- 

 phone or an automobile work? 



Secure an old telephone 

 magneto of the type shown 

 in Figure 392. Study its 

 construction carefully, 

 noting the method of pro- 

 ducing the magnetic field, 

 the coil, and the provisions 

 that are made for turn- 

 ing the coil rapidly in the 

 magnetic field. 



Write a summary para- 

 graph showing how Fara- 

 day's experiment is made to work in a magneto generator. 



Experiment 155. How does a modern electric genera- 

 tor work? 



A toy electric motor such as those used with Meccano 

 and Erector sets, a St. Louis motor, or a small electric 

 generator may be used for this experiment. Attach a table 

 galvanometer or the one used in Experiment 153 to the 

 binding posts of the small generator. If the St. Louis motor 

 is used, attach the electromagnet field and place a dry cell 

 in the circuit as shown in Figure 393. Turn the armature 

 (the moving part of the generator) with the fingers. Notice 



FIG. 392 



the galvanometer needle. Turn the armature in the opposite 

 direction. Record your observations. How is the magnetic 

 field obtained? How is the current which is generated in" 

 the armature taken to the outside ? Spin the armature and 

 notice the galvanometer needle. Does it vibrate back and 

 forth or move only in one direction? In your notebook 

 record the notes of the experiment and complete the fol- 

 lowing statements. 



The magnetic field of the generator studied is produced 



by an magnet. The moving part of the generator is 



called the This might be turned in the magnetic* field 



by ^_ power 'or power. Current is generated in the 



because _ _ of wire are made to _ _ across _ 



of force. The current generated in the 



is taken to an 



FIG. 393 



outside circuit such as the galvanometer through 



OTHER INVESTIGATIONS WHICH YOU CAN MAKE 



1. Visit an electric power plant and study the large 

 generators. 



2. Connect a small generator to a toy steam engine and 

 have a model power plant. 



3. Construct a model water-power plant with a small 

 generator and a water motor. 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



What did Michael Faraday discover about mag- 

 netism and electricity, and how was it put to work? 

 Michael Faraday was one of the world's greatest 

 experimenters. Without much education but with 

 tremendous determination arid sacrifice, he followed a 

 career in the laboratory of the Royal Institution in 

 London because of his great love of science. He made 

 many discoveries, but perhaps his greatest was that 

 an electric current could be obtained by moving a 

 coil of wire over a magnet. This came about twelve 

 years after Oersted had made his discovery that every 

 conductor carrying an electric current has a mag- 

 netic field about it. It is not difficult for us, living in 

 an electrical age, to see that Faraday's discovery is 

 one of the most important of all time. Because of his 

 great generosity Faraday did not patent his discovery. 

 Every light that burns, every electric heating device 

 and motor make use of current which comes from a 

 generator applying the principle of Faraday's experi- 

 ment. 



Exercise. After carefully reading the foregoing para- 

 graph about Michael Faraday, make a list of the traits 

 zvhich he had that in your judgment made him a great 

 scientist. 



Electricity is generated in a conductor that cuts 

 across magnetic lines of force. It makes no differ- 

 ence whether the coil or the magnet be moved, just as 

 long as the lines of force are broken. The amount 

 of electrical energy obtained in this way depends upon 

 three things the number of lines of force, the number 

 of conductors or coils of wire, and the speed with 

 which the lines of force are cut. The direction in which 

 the electric current flows in the coil depends upon the 

 direction in which the lines .of force are cut. For ex- 



