Magnetic Force on a Charge
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Forces on moving charges in magnetic fields
A magnetic field grabs a charged particle only when it moves, and even then only when the motion has a component across the field lines. Parallel travel earns no force at all; perpendicular travel earns the maximum, which is why electron beams bend sideways — never forwards — as they cross a field.
What you know already
A magnetic field picks on moving charges only — and even then only when they cut across the field lines. This note pins down the two conditions for the force, the perpendicular maximum, the parallel zero, and why a deflected beam changes direction without changing speed.
Key points of understanding
- A charged particle experiences a force in a magnetic field only while it is moving.
- The force vanishes when the particle moves parallel to the magnetic field lines.
- The force is greatest when the motion is perpendicular to the field lines.
- The force direction depends on the sign of the charge, so electrons deflect opposite to positive charges.
- The force acts at right angles to both the motion and the field, so it changes direction, not speed.
The electron experiences a force upwards when it travels through the magnetic field between the two poles. Remember that conventional current flows in the opposite direction to electrons.
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1.Forces on moving charges in magnetic fields
A magnetic field grabs a charged particle only when it moves, and even then only when the motion has a component across the field lines. Parallel travel earns no force at all; perpendicular travel earns the maximum, which is why electron beams bend sideways — never forwards — as they cross a field.
The electron experiences a force upwards when it travels through the magnetic field between the two poles. Remember that conventional current flows in the opposite direction to electrons.
Key points
- A charged particle experiences a force in a magnetic field only while it is moving.
- The force vanishes when the particle moves parallel to the magnetic field lines.
- The force is greatest when the motion is perpendicular to the field lines.
Guided content from the SME authoring corpus — note rn_4cM2y5tCVYWZ9VMJ, pinned at 6312d659ec0d · promoted SyllabAI/syllabai-resources b3caaaa90c5e