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6.1.9Chemical Reactions

Magnetic Field Patterns — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 19 of 21 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Section 1 of 5Field Shapes

Each shape of conductor produces a characteristic pattern of field lines.

Straight wire
  • Straight wire Concentric circles around the wire that spread further apart with distance, with direction given by the right-hand thumb rule.
Flat circular coil
  • Flat circular coil Field lines pass through the centre of the coil and circle around each turn, so the field is strongest near the centre of the loop.
Solenoid
  • Solenoid A long coil whose external field resembles a bar magnet's field, with its north and south poles at the two ends.
Uniform region
  • Uniform region Parallel, equally spaced lines inside a long solenoid show a uniform field along the central axis.

Section 2 of 5Finding Solenoid Poles

The polarity of a solenoid depends on the direction the current takes around the coil, seen from one end.

1
View the solenoid from one end, because the direction of the current depends on which end you look at.
2
If the current runs clockwise when viewed from that end, that end is a south pole.
3
If the current runs anticlockwise when viewed from that end, that end is a north pole.
4
Reversing the direction of the current swaps the north and south poles of the solenoid.
5
Inside the solenoid the field runs from the south pole to the north pole, which is the same as inside a bar magnet.

Section 3 of 5Factors Affecting Strength

Strength depends on the current, the number of turns and the presence of a core.

Factors Affecting Strength
More current
  • More current Increasing the current increases the strength of the field around a straight wire, a coil or a solenoid.
More turns
  • More turns Increasing the number of turns per unit length of a solenoid strengthens its internal field.
Shorter solenoid
  • Shorter solenoid For a fixed number of turns, a shorter solenoid gives a stronger field because its turns are more concentrated.
Iron core
  • Iron core An iron core inside a solenoid becomes an induced magnet and greatly increases the overall field strength.

Section 4 of 5Worked Example

Question Explain why the field inside a long solenoid is more uniform than the field outside it.

  1. Recall that the fields from the individual turns add together inside the solenoid.
  2. Along the centre of a long solenoid the contributions from the turns combine to give a nearly constant field.
  3. Outside the solenoid the field from the turns partly cancels, so it is weaker and less uniform.

Answer Inside a long solenoid the fields add together to give a strong, almost uniform field, while outside it the fields cancel and the field is weaker.

Section 5 of 5Exam Checklist & Tips

6.1.9 – Key Points for the Exam

  • Solenoid A long coil of wire whose field inside is strong and nearly uniform.
  • Flat circular coil A single loop or set of loops whose field lines pass through its centre.
  • Concentric circles Circles sharing a centre, which describe the field around a straight wire.
  • Uniform field A field with the same strength and direction at all points, shown by parallel lines.
  • Turns
    • The loops of wire in a coil;
      • the field strength depends on the number of turns.

Common Mistakes

  • Saying the field around a wire has poles; it forms circles with no poles.
  • Saying add more coils rather than add more turns to the coil.
  • Drawing the external field of a solenoid as stronger than its internal field.
  • Confusing the poles of a solenoid by viewing it from the wrong end.

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Transformer Golden Equations Physics Standard

Transformer Turns Ratio & Efficiency

Ratio: Vp / Vs = Np / Ns = Is / Ip

  • Step-up reduces grid thermal loss (P = I2R).
  • Laminated core prevents eddy currents.
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