6.11 to 6.14 Plenary questions
2 a) left
b) commutator, turn
9. out of the page
Sunday, January 22, 2012
6.14
6.14
01 December 2011
18:05
· 6.14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current
<<dc motor - factors affecting the speed of a motor interactive.swf>>
Exam style question
· What changes can you make to a simple dc motor to increase the force it can exert? (3 marks)
Model Answer
· Increase the strength of the magnetic field
· Increase the current in the coil
· Increase the number of turns on the coil
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)
<<Magnetic fields interacting - Force on current carrying wire.swf>>
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
<<FLHR practice.pptm>>
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-conductor-si-13208
6.13 Plenary
12 December 2011
11:55
<<FLHR Animation - Force on current carrying wire.swf>>
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
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)
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
6.11
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
Timelapse of aurora
Thursday, January 19, 2012
PFY P.300 Phsyics.
PFY p.300
1. A) The lines of magnetic field round a straight current- carrying conductor are in the shape of circle
B) The Right-hand Grip Rule: if you grip the wire with your right hand pointing with the conventional current, your fingers curl with the magnetic field lines.
C) For a solenoid, the magnetic field is like that of a bar magnet.
D) If a coil is viewed from the one end and the current flows in an anticlockwise direction, then this end is a North pole.
E) The magnetic effect of a coil can be increased by increasing the number of turns/coils, increasing the magnetic field strength, or inserting a – core.
For the coil in the diagram, when the switch is pressed:
a) What is the polarity of end A? -
b) Which way will the compass point then? -
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