This mini-lesson covers Themes D.1–D.3 — Fields: gravitational fields and Newton's law, electric fields and Coulomb's law, magnetic fields, and the motion of charges in electric and magnetic fields.
Work through each screen, answer the questions as you go (some are reasoning, some are calculations) and collect ⭐ stars. Watch for the HL flag on higher-level extensions. Press Start when you're ready.
A field is a region where a mass or charge feels a force. Gravitational field strength g is the force per unit mass. Newton's law of gravitation and the field of a point/spherical mass are inverse-square:
Gravity is always attractive and acts on mass. Because g ∝ 1/r², doubling the distance from a planet's centre quarters the field strength.
Electric field strength E is the force per unit positive charge. Coulomb's law gives the force between point charges, and a point charge produces a radial field:
Unlike gravity, electric forces can attract or repel: like charges repel, unlike attract. Field lines point away from positive charge and towards negative.
A magnetic field exerts a force on a moving charge or a current. The force is perpendicular to both the field and the velocity/current (Fleming's left-hand rule):
Because the magnetic force on a moving charge is always perpendicular to its velocity, it does no work — it changes direction, not speed, making charges move in circles.
Tap an item, then tap the group it belongs to.
Tap a statement on the left, then its match on the right.
Gravitational: g = GM/r²; F = GMm/r²; attractive, acts on mass
Electric: E = kQ/r²; F = kQ₁Q₂/r²; attracts or repels
Magnetic: F = BIL and F = qvB; force ⟂ velocity, so does no work
Inverse square: doubling r quarters both gravitational and electric field
Field lines: out of + charge, into − charge; toward a mass
That completes Fields for IB Diploma Physics SL. Press Finish to see your score.
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