6.12

6.12

01 December 2011

18:05

·         

6.12 recall that a force is exerted on a current-carrying wire in a magnetic field, and how this effect is applied in simple d.c. electric motors and loudspeakers

6.12 Practical - dc motor

12 December 2011

15:29

·         Connect a dc motor to a power pack

·         How you can reverse the direction of spin of the motor? (2 ways)

·         How you can make a stronger turning force on the motor? (2 ways)

3.  How can you see that the turning force is stronger?

Answers

1.               

a.                  Reverse the poles of the magnets

b.                  Reverse the direction of the current in the coil by switching over the polarity of the wires to the power pack

2.               

a.                  Increase the current in the wire (by increasing the voltage of the power pack)

b.                  Increase the strength of the magnetic field (by adding more magnets to the yoke)

 

3.              The motor spins faster which indicates a larger turning force

6.12 dc motor simulation

28 November 2011

15:06

Website:

http://www.walter-fendt.de/ph14e/electricmotor.htm

Embed code for your blog:

<iframe src="http://www.walter-fendt.de/ph14e/electricmotor.htm" style="border:0px #FFFFFF none;" name="myiFrame" scrolling="yes" frameborder="1" marginheight="0px" marginwidth="0px" height="800px" width="800px"></iframe>

6.12 loudspeakers

12 December 2011

15:37

	<<Loudspeaker demo with voice over.swf>>		<<animated loudspeaker - slow and clear.swf>>

Exam style question

·         Explain carefully how an alternating current in the coil of a loudspeaker can create a sound (4 marks)

Model Answer

Any four points from...

·         When a current flows in the coil, it is perpendicular to the magnetic field

·         This creates a force on the coil, due to the motor effect, and so the coil moves

·         When the alternating current reverses direction, the direction of the force is also reversed and the coil moves in the opposite direction

·         The moving coil is attached to a cone which also moves backwards and forwards. 

·         This makes air particles vibrate and this is the sound we can hear

Loudspeaker demo with voice over.swf Download this file

animated loudspeaker - slow and clear.swf Download this file