Short interactive lessons that ask a question before they explain. One session takes about ten minutes and ends with questions to check what you have understood.
A set is a well-defined collection, written in roster form or in set-builder form.
Class 11 · Maths Sets FreeEmpty, finite, infinite and equal sets. Equal sets have exactly the same elements.
Class 11 · Maths Sets FreeSubsets, the 2ⁿ subsets in a power set, and intervals as subsets of the real line.
Class 11 · Maths Sets FreeThe universal set contains everything under discussion; Venn diagrams show sets as regions.
Class 11 · Maths Sets FreeUnion, intersection, difference and complement, each a region of a Venn diagram.
Class 12 · Physics Charge and the Field Around It FreeLike charges repel and unlike charges attract. Charge is additive, conserved and quantised.
Class 12 · Physics Charge and the Field Around It FreeThe force between two point charges is proportional to their product and to 1/r².
Class 12 · Physics Charge and the Field Around It FreeThe total force on a charge is the vector sum of the forces each other charge exerts alone.
Class 12 · Physics Charge and the Field Around It FreeThe field is the force per unit charge at each point. A charge q in a field E feels F = qE.
Class 12 · Physics Charge and the Field Around It FreeField lines show the field’s direction and strength; flux Φ = EA cos θ measures the field through a surface.
Class 12 · Physics Charge and the Field Around It FreeEqual and opposite charges a small distance apart. In a uniform field: no net force, but a torque pE sin θ.
Class 12 · Physics Charge and the Field Around It FreeThe flux out of any closed surface equals the enclosed charge divided by ε₀.
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