ELECTRICITY AND MAGNETISM TEST

 

                                                            NAME:         

 

      Choose the most correct answer.

 

      1. Consider the following factors for a magnet moving inside a coil:

      I.    the strength of the magnet

      II.   the number of turns in the coil

      III   the speed at which the magnet moves

 

      Which of the following factors can affect the size of the voltage induced in the coil

      a) I only

      b) II only

      c) III only

      d) I and II only

      e) I, II and III

 

      2. To use the Left Hand Helix Rule you must point your left thumb

      a) toward the S pole of the helix

      b) toward the N pole of the helix

      c) toward the negative terminal of the battery

      d) in the direction of electron flow

      e) in the opposite direction of electron flow

 

      3. Which of the following factors does not affect the strength of an electromagnet?

      a) the direction of the windings

      b) the diameter of the core

      c) the number of turns in the coil

      d) the permeability of the core

      e) the resistance of the coil wire

 

      4. The brushes of a D.C. motor

      a) allow the armature to rotate while still being connected to the battery

      b) connect the armature to the permanent magnet

      c) keep the armature free of dust

      d) prevent sparking within the motor

      e) reverse the polarity of the field magnet at regular intervals

     

      5. A permanent magnet is held stationary in the centre of a coil connected to a galvanometer. The current reading on the galvanometer will

      a) be steady and zero

      b) be steady and not zero

      c) steadily increase

      d) steadily decrease

      e) steadily increase and then decrease

 

      Short answer

     

      1. For the following diagrams indicate the direction of flow of electrons as well as the N and S poles.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

      2. There are two types of transformers. Indicate which type you would find near the hydroelectric plant, and which you would find on the pole near your house, also explain the difference.

 

 

 

  

 6

 

 

 

 

 

 

      3. You have an initial voltage of 200V you wish to increase this to 500000V, if the primary coil has 30 turns how many turns should the secondary coil have?

 

 

 

  

 3

 

 

      4. Explain the method by which an electric bell works.

      ( a labelled diagram would be a really good idea)

 

 

 

  

 5

 

 

 

 

 

 

 

 

 

 

      5. Why will transformers not work if the supply current is D.C.?

 

 

  

 3

 

 

 

 

 

 

      6. What advantage is there to transformers?

 

 

  

 3

 

 

 

      7. If the transformer you have has a primary coil with 200 turns and a secondary coil with 8000 turns, and you want the secondary voltage to be 16000V, what must the primary voltage be?

 

 

  

 3

 

      8. Label the following diagram of an A.C. motor. Indicate polarity of field magnet to achieve desired rotation.

 

 

 

 

 

  

 4

 

 

 

 

 

 

 

      9.  Label the following diagram of an D.C. motor. Indicate polarity of field magnet to achieve desired rotation.

 

 

 

 

 

 

 

 

 

 

  

 4

 

 

 

 

 

 

 

      10. What increase in efficiency is achieved by using a transformer that has 2 turns on the primary coil and 20 turns on the secondary coil, when the initial voltage is 200V, if the resistance in the conductor is 1.0 ohm. ( you must determine the loss of power as a result of not using the transformer as compared to the loss using the transformer.)

 

 

 

 

   

 10

 

 

 

 

 

 

 

      11. An electric steam iron is marked "10A, 110V". How much will it cost to operate the iron for 3 hours if the energy cost is $0.10/kW*h?

 

 

 

  

 8

 

 

 

 

      12. A refrigerator draws 2.5 A from a 120V source and operates on average 12 minutes out of each hour. Calculate the approximate cost of operating the refrigerator if the cost of electricity is $0.12/kW*h.

 

 

 

  

 10

 

 

 

 

 

 

 

 

      13. State LENZ's Law.

 

  

 2