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GCSE level Physics exam revision notes:
Electromagnetism
10.2 Solenoid coil
-
its design and function
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electromagnetism and its uses
10.2
The solenoid coil -
its design and function
How do you make a magnet using
electricity?
We have seen that a single current
carrying wire produces a magnetic field of concentric lines of force.
This in itself is of little use, but,
there are ways of increasing the magnetic field effect to produce something
of use in many 'electromagnetic' applications.
See also
Part 10.3
How
to increase the magnetic field strength of a solenoid coil?
 no
soft-iron core
Plot of the magnetic field created by a solenoid coil
when a d.c. current is passed through it,
with or without a soft iron core - note the symmetrical coiled shape of the
coil of wire of the solenoid.
For the diagram of the
magnetic field produced by a solenoid coil, note the linear and denser
concentration of the lines of force down the centre of the coil.
with a soft iron core
A solenoid coil containing a soft
iron core, around which is coiled insulated copper wire.
The magnetic field lines of flux become
more concentrated, particularly at the poles, showing an increase in the
strength of the magnetic field.
An effective solenoid needs to consist of
hundreds of coils of finely wound insulated copper wire.
Such an iron-cored solenoid coil can act as a
temporary magnet as long as a d.c. current is flowing.
The
principles of a functioning solenoid
See also
Part 10.3
How
to increase the magnetic field strength of a solenoid coil?
If you coil the wire in a compact way (as
in the diagrams above) you can greatly intensify the magnetic field effect.
The stretched out resulting current
carrying coil is called a solenoid and can act as an electromagnet which
can be switched on and off depending whether current is flowing
or not i.e. acts as a temporary magnet.
You can 'construct' this magnetic
field diagram using a plotting compass to map the magnetic field of a
steel bar permanent magnet.
Inside the coils, the increase in
field strength is due to all the lines of force lining up with
each other and close together too - intensifying the magnetic
field effect at what is effectively another north-south pole situation.
Remember - the closer the lines
of force the greater the strength of the magnetic field at that
point.
So, note the
uniformity and
intensity of the magnetic field inside the coil, which is much
weaker outside the coil because lots of overlapping lines of force
around each coil cancel each other out.
The magnetic field is overall
weak except at the ends of the solenoid where it is very strong.
Note: The magnetic field pattern
outside the solenoid is just the same as a
bar
magnet, with a north and south pole and the magnetic flux
lines flowing from north to south.
Polarity of a solenoid coil
You can work out the polarity of a
solenoid by viewing the end of the solenoid and observing the direction
of the convention current is flowing.
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electromagnetism and its uses
Key points about electromagnetism
- the
solenoid coil
Information
sources for Doc Brown's key points: IGCSE-GCSE physics are based on
textbooks & syllabus-specifications for students taking the UK AQA, Edexcel,
OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE
physics 9-1 level science examinations
Here's a comprehensive set of
summary revision notes on solenoid coils,
tailored to the GCSE/IGCSE Physics specifications
across major UK exam boards (AQA, Edexcel, OCR, WJEC, CCEA, CIE):
Solenoid Coil – Structure and Function
Structure of a Solenoid
- A solenoid is a
long coil of insulated wire wound in a helical
(cylindrical) shape.
- When an electric current
flows through it, a magnetic field is produced.
- Often wrapped around a soft
iron core to form an electromagnet.
Magnetic Field of a Solenoid
- Inside:
Strong, uniform, and parallel magnetic
field lines (like a bar magnet).
- Outside:
Field resembles that of a bar magnet with distinct
north and south poles.
- Direction
of the field is determined using the right-hand grip rule:
- Fingers curl in the direction of
current.
- Thumb points to the north
pole of the solenoid.
Typical Exam Board-Specific Content
|
Key
Requirements |
| Describe magnetic field patterns
in solenoids; explain how solenoids increase magnetic field
strength; define electromagnets. |
| Explain how solenoids produce
uniform magnetic fields; describe how to increase field strength;
relate to electromagnets. |
| Understand solenoid field
patterns; describe how field strength is affected by current, turns,
and core material. |
| Describe the structure and
magnetic field of solenoids; explain how they are used in
electromagnets. |
| Explain solenoid field patterns;
describe how to increase field strength; relate to applications like
relays and bells. |
| Describe the magnetic field of a
solenoid; use the right-hand rule; explain how solenoids are used in
electromagnets. |
Factors Affecting Magnetic Field Strength
Common Applications of electromagnetism
Student Tips for Exams
- Draw field lines:
Inside = parallel and close; outside = like a bar magnet.
- Use correct terminology:
Say “turns of wire” not “coils”.
- Explain polarity:
Clockwise = south pole; anticlockwise = north pole (viewed from end).
- Link to electromagnets:
Emphasise that solenoids become electromagnets with iron cores.
- Practice diagrams:
Label poles, field lines, and direction of current clearly.
Keywords, phrases and learning objectives
on electromagnetism
Be able to describe the design, structure and function of a solenoid coil.
Know that a solenoid consists of many turns of
insulated copper wire.
Know, and be able to describe how to plot the
magnetic field around a solenoid coil.
Know how to predict
the polarity of the magnetic field around a solenoid coil.
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