Summary

• Faraday's law
• Magnetic flux

• Class Quiz
  
  
• Transformers
  • principle of operation
  • voltage & current
  • power
    
    Example #1
    
    Example #2
    
    Example #3
    
    
  
  
  

gc6 tb 21.14
A bar magnet falls straight down through a loop of wire with the north pole entering first. As the north pole enters the loop, the induced current will be (as viewed from above)
A. zero
B. clockwise
C. counterclockwise
Answer







klm
A step-up transformer has an input voltage of 100 V and an output voltage of 1000 V. If half of the loops in the secondary coil are transferred to the primary coil, what will the new output voltage be?
A. 120 V             B. 500 V
C. 250 V             D. 83.3 V
Answer







gc6 21.76
The primary windings of an 80% efficient transformer are connected to 110 V. The secondary windings are connect across a 2.4 Ω, 75 W lightbulb. What is the current in the primary coil?
A. 0.682 A          B. 0.852 A
C. 1.17 A            D. 1.47 A
Answer







gc6 21.76
The primary windings of an 80% efficient transformer are connected to 110 V. The secondary windings are connect across a 2.4 Ω, 75 W lightbulb. What is the ratio N_P / N_S?
A. 8.2             B. 5.6
C. 3.0             D. 1.2
Answer







 



C. counterclockwise
By Lenz's law the loop will attempt to produce a magnetic field pointing upwards in order to oppose the downwards pointing field of the falling magnet. Use the right hand rule to verify the current must flow counterclockwise in order to produce the opposing magnetic field.












 



D. 83.3 V













 



B. 0.852 A













 



A. 8.2