Transcript The Strength of an Electromagnet - School

The Strength of an
Electromagnet APP
This has been part of the KS3 syllabus since the
inception of the National Curriculum. The section on
magnetism in Y8 has included a review of permanent
magnetism and its laws.
1.A permanent magnet has two poles- North and South.
2.The region around a magnet where it can attract magnetic materials is called a
magnetic field. This is a three dimensional region and it is strongest near the poles.
3.Permanent magnets have uses in the compass, door catch, fridge door seal etc
N
S
The Strength of an Electromagnet
A permanent magnet cannot be switched on or off nor can its strength
be changed so a better magnet is needed where control of the strength
is essential.
Oersted discovered that when a wire carries an electric current it forms
a magnetic field around it. This field is stronger if :
a) the current is greater
b) the wire is coiled into a shape called a solenoid
c) a core of iron is placed inside the solenoid
Switch is open so no current flows
Electromagnet
is OFF
Coil or ‘solenoid’ with
turns of insulated wire
‘soft’ iron core
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The Strength of an Electromagnet
The theory of magnetism in a metal like iron says that there are small
areas of magnetism inside the metal called DOMAINS. Normally, these are
randomly arranged so their magnetism cancels out. If a magnetic field
surrounds the metal, the domains can be aligned in the SAME DIRECTION so
their magnetism adds up until it reaches a maximum power.
Switch is closed so current flows
Electromagnet
is ON
The solenoid magnetises
the iron so it will deflect a
compass
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The Strength of an
Electromagnet
If the core is shaped into a horseshoe, the strong field near each pole can be used to
lift an object such as a nail. This is the familiar shape of an electromagnet.
If some masses are hung from the nail, then the strength of the electromagnet can
be tested.
Iron ‘C’ core
‘turns’ of
insulated wire
2 volt power pack
Iron nail
Mass hanger
Slotted masses
10g, 20g, 100g
Equipment for the experiment
1. ‘C’ core
2. Length of insulated wire
3. Iron nail
4. Mass hanger
5. 12 volt power pack
6. Set of 10g, 20g and 100g masses.
7. Retort stand, clamp and boss.
8. Clamp to hold the stand secure.
9. Prepared table for your results
10.Electric balance.
To do:
Name on your sheet.
Results table (with repeats if you
had time)
Construct a graph of no. of turns (xaxis) mass held (y-axis)
Draw a line of best fit
Lable axes with units if appropriate.
Answer the four questions on the
sheet.
Hand in your sheet and the graph
No. of
turns
5?
Mass 1
(g)
10?
Nail + hangar
13?
Nail + hangar
+ 1 mass?
nail
Repeat 2 Repeat 3 Average
(g)
(g)
mass (g)
(Mass 1 + Repeat 2 +
Repeat 3 )/ 3
- Measure the mass of the nail, and of the hangar,
write them down.
- See how many coils you need to hold the nail,
write it down and the mass of the nail.
- Add on coils 2 at a time, until it holds the nail
and the hangar, write down the combined mass.
- Add on coils until it holds an additional 10g and
record the number of coils and total mass of nail,
hangar and weight.
- Continue until you have held 4 to 5 masses.
- Repeat from the beginning.
- Take the average mass.
- Plot a graph of no. of turns against mass held.
Plot the number of turns on the x-axis and the
mass held (g) on the y-axis as a point graph.
No. of turns
12
14
16
18
20
22
50
45
40
Mass held (g)
Average
Mass it will hold / g
35
30
25
20
15
10
5
0
0
10
20
30
40
50
Number of coils
60
70
80
90
In this investigation, these factors stay the same.
The total length of insulated wire.
The power pack so the current stays the same.
The nail and the mass hanger (you must weigh them both first)
The iron core
The factor that you change is the number of turns of insulated wire.
Start with the least number that will hold the nail (at least 12), record the mass
Then see if it will hold the mass hanger, if it does record that mass.
Iron ‘C’ core
‘turns’ of
insulated wire
2 volt power pack
Iron nail
Mass hanger
Slotted masses
10g, 20g, 100g
The Strength of an Electromagnet
Now increase the number of turns by 2. See if it will hold any more masses.
Write your results in a table. Keep going for at least another 6 results.
You must also repeat your results.
Watch for a pattern.
Iron ‘C’ core
‘turns’ of
insulated wire
2 volt power pack
Iron nail
Mass hanger
Slotted masses
10g, 20g, 100g