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

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

dc motor - factors affecting the speed of a motor interactive.swf Download this file

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

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

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>>

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

6.11

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

 

6.8 to 6.10

6.8 Field around current carrying conductor simulation

28 November 2011

15:06

Website:

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

Embed code for your blog:

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

6.8 and 6.9

01 December 2011

18:04

·         

6.8 recall that an electric current in a conductor produces a magnetic field round it

·         6.9 describe the construction of electromagnets

	<<Electromagnets.ppt>>		<<magnetic field around wire and a solenoid.swf>>

6.8 and 6.9 extension - bell

01 December 2011

18:04

	<<electric bell animation.SWF>>

6.8 and 6.9 Plenary Multichoice questions

01 December 2011

18:13

<<6c Plenary Multichoice questions.pptx>>

6.10

01 December 2011

18:04

·         6.10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current

Straight wire = Right hand grip rule

Flat circular coil

Solenoid

6.8 to 6.10 Plenary questions

magnetic field around wire and a solenoid.swf Download this file

Electromagnets.ppt Download this file

Electromagnet lifting a car.swf Download this file

electric bell animation.SWF Download this file

6c Plenary Multichoice questions.pptx Download this file

pfy p.300

2. a) The lines of the magnetic field round a straight current carrying conductor are in the shape of concentric circles
b) The right-hand grip rule: if you grip the iron core with your right hand pointing with the thumb, 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 one end and the current flows in an anti-clockwise direction, then this end is a north pole
e) The magnetic effect of a coil can be increased by increasing the number of turnes in the coil, increasing the current, or inserting an iron core

3. a) south
b) east

5.19 Boyle's Law

5.19 Boyle's Law demos

02 November 2011

20:01

	<<Video - mixing colours in a bell jar with Boyle's law.flv>>

Fun with the vacuum pump!

·         

Marshmellows

·         Food colouring in pipettes

·         Surgical gloves

5.19 Experiment

07 November 2011

14:32

·         

Change the pressure of a fixed mass of gas at a constant temperature

·         Measure the volume

·         Use the EXCEL spreadsheet to analyse your results

Ideal Gas - Boyle's Law.xlsx Download this file