Dee Dee's Physics Blog

6.7

6.7 starter
01 December 2011
19:37
Tell the person next to you…
1.              If the field lines are close together, what does this tell you about the field?
2.              If the field lines are widely spaced, what does this tell you about the field?
3.              If the magnetic field lines are parallel to each other, what does this tell you about the field?
Answers
1.              The field is strong
2.              The field is weak
3.              The field is of a constant strength - a "uniform" field

6.7
28 November 2011
15:08
·         6.7 know how to use two permanent magnets to produce a uniform magnetic field pattern

·  When the field lines are parallel, the field will be uniform

See the full gallery on Posterous

6.4

6.4
28 November 2011
15:07
•        6.4 understand the term ‘magnetic field line’
Observing the magnetic field around a bar magnet and a wire
magnetic field around a bar magnet and wire
·
Use iron filings to observe the magnetic field around a bar magnet
·         Use plotting compasses to observe the field
·         Use the 3D field demonstrator to observe field

6.4 Field around bar magnet simulation
28 November 2011
15:06
Website:
http://www.walter-fendt.de/ph14e/mfbar.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>
Example:
http://maddog11physics.posterous.com/bar-magnet
6.4 plenary questions and Earth's Magnetic Field
01 December 2011
19:12
<<Plenary questions and the Earth's Magnetic field.ppt>>

Plenary questions and the Earth's Magnetic field.ppt 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

6.13

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:
<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

6.6

6.6
28 November 2011
15:07
·
6.6 sketch and recognise the magnetic field pattern for a permanent bar magnet and that between two bar magnets

6.18

01 December 2011

18:08
· 6.18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy
· http://youtu.be/LZKhGGBcYFI
>

6.18 answers

01 December 2011

18:08
[cid:image001.jpg@01CCE4AC.9D422F50]
[cid:image002.png@01CCE4AC.9D422F50]
[cid:image003.png@01CCE4AC.9D422F50]

National grid worksheet.doc Download this file

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6.20

01 December 2011

18:08
· 6.20 recall and use the relationship (for 100% efficiency):

input power = output power

Vp Ip = Vs Is
>

6.19 and 6.20 Plenary answers

01 December 2011

18:08
[cid:image001.png@01CCE4AC.921B9210]
a. Vs/Vp=ns/np

Vs/2=80/20

Vs=8V

b. Vs/Vp=ns/np

Vs/10=20/100

Vs=2V

c. Vs/Vp=ns/np

Vs/240=20/400

Vs=12V

d. Vs/Vp=Ns/Np

Vs/4=2000/50

Vs=160V

[cid:image002.jpg@01CCE4AC.921B9210]
2. Vs/Vp=ns/np

3/24=ns/480

ns=60turns

[cid:image003.jpg@01CCE4AC.921B9210]
a. Iron (Why? Iron is a magnetically soft material - it can be magnetised and lose its magnetism easily. This is necessary in a transformer as the magnetic field needs to change repeatedly)
b. electrical energy in the primary coil => magnetic energy in the core =>electrical energy in the secondary coil
c. dc current produces a steady magnetic field in the core. To induce a current in the secondary coils there must be a changing magnetic field in the core.

[cid:image004.jpg@01CCE4AC.921B9210]
a. Step down (because the voltage decreases)

b. Vs/Vp=ns/np

12/240=ns/1000

ns=50turns

c. P = V x I

24 = 12 x I

I = 2A

d. Power in secondary = 24W

e. Power in primary = 24W

f. P = V x I

24 = 240 x I

I = 0.1A