ELECTROMAGNETIC DEVICES WORKSHEET - eng
Оценка 5

ELECTROMAGNETIC DEVICES WORKSHEET - eng

Оценка 5
docx
08.05.2020
ELECTROMAGNETIC DEVICES WORKSHEET - eng
ELECTROMAGNETIC DEVICES WORKSHEET - eng.docx

                     ELECTROMAGNETIC DEVICES QUIZ( 20 MKS)

1.      a) Name the device sown below:

 

…………………………………………………………………………………………………………………….{1 mk}

b) Briefly explain how the device above operates.                                              {4mks}

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

c) Where would you find the device in its practical application?                         {1mk}

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

2.      A) State any three ways of improving the emf produced by a generator.               {3mks}

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

b) A square coil is placed in a uniform magnetic field of flux density 40 mT. The plane of the coil is normal to the magnetic field. The coil has 200 turns and the length of each side of the coil is 3.0 cm.

a Calculate:

i the magnetic flux Φ through the coil [2]

ii the magnetic flux linkage for the coil. [2]

b The plane of the coil is turned through 90°. What is the change in the magnetic flux linkage for the coil?

 

3.     The diagram shows a step-down transformer. The primary coil has 1150 turns and the secondary coil has 30 turns. The ends of the secondary coil are connected to a lamp labelled ‘6.0 V, 24 W’. The ends AB of the primary coil are connected to an alternating voltage supply. The potential difference across the lamp is 6.0 V.

 

27                  

 

 

 

 

 

 

a.   Calculate the current in the lamp.                                                            [2]

 

 

b. Calculate the input voltage to the primary coil.                                          [2]

 

 

c. Calculate the current in the primary coil, assuming the transformer is 100% efficient.      [2]

 

 

 

d. A student suggests that to avoid the production of heat in the transformer the wires should be coated in a material that is a poor conductor of heat. Explain why this is not a sensible suggestion.                                                                                           [1]

................................................................................................................................................................................................................................................

 

 

ANSWERS

1a) Electromagnetic relay

b) When the switch is closed, the electromagnet is magnetized and attracts one end of the iron armature. The contacts closes (2nd switch) and allows current to flow in the second circuit. When the 1st switch is open again, the current to the electromagnet is cut, the electromagnet demagnetizes and the 2nd switch is opened. Current stops flowing in the second circuit.

c)  in industries( controlling large power loads),electric fuel pump, motor control

2a) Increasing the speed of rotation

       Increasing the number of turns

      Using horse-shoe magnet

b)

3.

a) P=IV, I= 4 A.

b)  = = ; Voltage in primary = 230V.

c) Using the equation in b) above, : I= 0.104 A

d) Heating of a transformer is independent of the coating on the wires as it occurs within the wire.


 

ELECTROMAGNETIC DEVICES QUIZ( 20

ELECTROMAGNETIC DEVICES QUIZ( 20

A square coil is placed in a uniform magnetic field of flux density 40 mT

A square coil is placed in a uniform magnetic field of flux density 40 mT

Calculate the current in the primary coil, assuming the transformer is 100% efficient

Calculate the current in the primary coil, assuming the transformer is 100% efficient
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