2026-05-19 06:46

Status: #new

Tags: #physics #electromagnetism

4.7 Electromagnetism

Magnetic Field Lines

• This allows us to find the direction of a magnetic field
• The field goes from North Out, to South in a Closed Loop
• The closer the line is the higher the strength
• Field lines will never intersect (since they can never point in two directions at the same time)
• Illustration:
  

Magnetic Field and Current + Right Hand rule....

• The stronger the current the stronger the magnetic field
• Magnetic fields weakens with distance
• Field lines can be seen as concentric circles (centred at the wire)
• Illustration:
  

Force on a current-carrying conductor in a magnetic field

• Recall: Newtons 3rd law, for every action they are is a equal and opposite reaction
• We can then infer that:
  • More current $\to$ More Force,
  • The maximum force is when the wire is perpendicular ($\perp$) to the magnetic field
  • The direction of the force acting on the wire depends on direction of the current and the direction of the field

Comparing Magnetic and Electric Forces

• $F_{mag}=q(\overrightarrow{V}\times \overrightarrow{B})\to q\Vert \overrightarrow{V}\Vert \overrightarrow{B}\Vert sin\theta$ (Magnetic Force)
• $F_{elec}=q\overrightarrow{E}$
• $F_{max}=\overrightarrow{V}\perp \overrightarrow{B}$
• $F_{min}=\overrightarrow{V}\parallel \overrightarrow{B}$ or $\overrightarrow{V}=0$

References

4.7 Electromagnetic Induction