Magnetic Fields: Exploring the Fundamentals in A-Level Science
What Is a Magnetic Field?
A magnetic field is a region where a magnetic force acts on moving charges or magnetic materials.
Field Representation: Magnetic field lines show the direction of the field, flowing from the north pole to the south pole of a magnet.
Magnetic Field Strength (B)
The strength of a magnetic field is measured in Tesla (T) and depends on the source and distance from it.
Formula for Magnetic Force on a Current-Carrying Wire
![\[ F = BIL \sin\theta \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-274e4432fbd8a209d3159911134ca6f2_l3.png "Rendered by QuickLaTeX.com")
Where:
: Force (N)- : Magnetic field strength (T)
: Current (A)
: Length of the conductor (m)- : Angle between and the conductor
: Force (N)
: Magnetic field strength (T)
: Current (A)
: Length of the conductor (m)
: Angle between Lorentz Force on a Moving Charge
A charged particle moving in a magnetic field experiences a force given by:
![\[ F = qvB \sin\theta \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-318e18274e57861f1c57580853900f01_l3.png "Rendered by QuickLaTeX.com")
Where:
: Charge (C)
: Velocity (m/s)- : Magnetic field strength (T)
: Charge (C)
: Velocity (m/s)Example: A proton (
) moves at 
perpendicular to a 
magnetic field. Find the force:
![\[ F = qvB = 1.6 \times 10^{-19} \times 2 \times 10^6 \times 0.5 = 1.6 \times 10^{-13} \, \text{N} \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-d179b21103197590fd8ecf0f1c24d1a7_l3.png "Rendered by QuickLaTeX.com")
Magnetic Flux and Flux Density
Magnetic Flux (Φ)
The total magnetic field passing through an area:
![\[ \Phi = B \cdot A \cdot \cos\theta \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-eca0f19011638d0125e9c6a6bc4baa26_l3.png "Rendered by QuickLaTeX.com")
Where 
is the area (
).
Applications of Magnetic Fields
Motors and Generators
Magnetic fields convert electrical energy into mechanical energy and vice versa.
Magnetic Resonance Imaging (MRI)
MRI machines use strong magnetic fields to create detailed images of the human body.
Particle Accelerators
Magnetic fields guide charged particles in circular paths.
Common Mistakes in Magnetic Field Calculations
- Forgetting to use the correct angle (
) - Confusing magnetic flux with flux density
- Mixing up units for Tesla, charge, or velocity
)Practice Questions
- Calculate the force on a
wire carrying a 
current in a 
magnetic field at . - Explain the concept of magnetic flux with an example.
- Describe one application of magnetic fields in medical imaging.
wire carrying a 
current in a 
magnetic field at 
.