6.12

·         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

·         

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

Website:

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

6.12 loudspeakers

12 December 2011

15:37

Exam style question

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

Gapfill Model Answer

·         When a ______ flows __ the ____, it is p____________ to the magnetic field

·         This creates a ______ on the coil, due to ___ _____ effect, and so the coil _____

·         When the _________ current reverses ______, the direction of the _______ is also reversed and the coil moves in the ________ direction

·         The moving ____ is attached to a ____ which also moves __________ and forwards. 

·         This makes ___ ________ vibrate and this is the _____ we can hear

 

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