Nik's IGCSE Physics: January 2012

Tuesday 31 January 2012

6.13

6.13 starter

12 December 2011

16:07

Practical - the current balance
· Use a current balance to investigate what happens when a current flows in a magnetic field
· How many magnetic fields are created by this apparatus?
· How could you make the wire move further? (2 ways)
· How could you change the direction the wire moves in? (2 ways)
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Answers
1. 2 magnetic fields:
a. the uniform magnetic field created between the poles of the permanent magnet
b. the magnetic field around the wire when the current flows
2.
a. Increase the current in the wire
b. Increase the strength of the magnetic field
3.
a. Reverse the poles of the magnets
b. Reverse the direction of the current

6.13

01 December 2011

18:05
· 6.13 use the left hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
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6.13 FLHR simulation

28 November 2011

15:06

Website:

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

Embed code for your blog:

Example:

http://maddog11physics.posterous.com/68-field-around-current-carrying-conduct...

6.13 Plenary

12 December 2011

11:55
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Magnetic fields interacting - Force on current carrying wire.swf Download this file

FLHR practice.pptm Download this file

FLHR Animation - Force on current carrying wire.swf Download this file

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:

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)
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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

6.11

01 December 2011

18:04
· 6.11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field

Solar wind creating aurora animation