226 Our Surroundings 



energy, the motor does the opposite thing; it changes electrical 

 energy, supplied by the dynamo, into the energy of motion. It is 

 another illustration of the transformation of energy. Electric 

 motors are used to drive elevators, trolley cars, washing ma- 

 chines, pumps, and many other types of machines. 



SUMMARY 



Man in recent times has made electricity available for many 

 practical purposes. 



Electricity and magnetism are not the same but are closely 

 related. 



An electromagnet is a piece of soft iron encircled by a coil 

 of insulated wire. 



Among the common applications of electricity are the door- 

 bell, the telegraph, and the telephone. 



A magnet induces a current of electricity when moved within 

 a coil of insulated wire. Such a current is called an induced 

 current. 



An induced current may also be produced by moving a coil of 

 wire in the magnetic field of a magnet. 



The dynamo is a machine for changing mechanical energy into 

 electrical energy. 



The transformer is a device for increasing or decreasing the 

 electrical pressure of a circuit. 



The electric motor is a machine for converting electrical energy 

 into mechanical energy. It is used for many industrial and domes- 

 tic purposes. 



FACT AND THOUGHT QUESTIONS 



1. In what practical ways have you used electricity? 



2. Upon what does the strength of an electromagnet depend? 



3. Describe the experimental work of Oersted. Why was it important? 



4. What important discovery was made by Henry and Faraday? 



5. Complete these statements orally : 



(a) The important parts of a telegraph circuit are . 



(b) An induced current is . 



6. Define a relay and explain its function. 



