Moving Charges and Magnetism — Class 12 CBSE Physics revision notes
A 7-page visual revision sheet for Moving Charges and Magnetism, written for Class 12 CBSE Physics. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Moving Charges and Magnetism in one look
a charge at rest feels nothing from B, a charge on the move feels everything
- Electric force: acts on any charge, moving or not
- Magnetic force: acts only on a MOVING charge, and only across its velocity
- Lorentz force: both together, the complete force on a charge
The magnetic force, said precisely
- F = qvBsinθ, θ is the angle between v and B
- direction from vtimesB: right-hand rule, then flip it for a negative charge
- always perpendicular to v: it can only turn a charge, never speed it up
- does zero work, so speed and kinetic energy never change
angle between v and B?
- θ = 0° or 180° — no force: v parallel or antiparallel to B, F = qvB sinθ = 0
- θ = 90° — circular path: F is always centripetal, radius stays fixed
- θ neither 0°, 90° nor 180° — helical path: component along B is untouched, component across B circles
Circular motion in a uniform field
- magnetic force supplies the centripetal force
qvB = mv^2/r - radius of the circle
r = mv/qB - period, independent of speed
T = 2π m/qB - cyclotron frequency
f = qB/2π m
Page 1 of 7. The full sheet, all 7 pages, opens free in the app.
What this Moving Charges and Magnetism sheet covers
- Electric force
- Magnetic force
- Lorentz force
- The magnetic force, said precisely
- Circular motion in a uniform field
- magnetic force supplies the centripetal force
- radius of the circle
- period, independent of speed
- cyclotron frequency
- A slanted entry: the helix
- Force on a current, not just one charge
- Biot-Savart law
- field from a current element
- vector form
- A long straight wire
- field at distance r from the wire
- A wire of finite length
- point P at distance r from the wire, angles θ_1, θ_2 to the perpendicular
- A circular current loop
- centre of a loop, N turns
- on the axis, distance x from the centre
- A loop is a magnet
- An arc of a circle
- centre of an arc of angle θ, radius R
- Ampere's circuital law
- any closed loop
- long straight wire, distance r
- Inside a thick wire
- inside, distance r from the axis, wire radius a
- outside the wire (r above a)
- Solenoid and toroid
- inside a long solenoid, n turns per length
- inside a toroid, N total turns
- Force between two parallel currents
- Torque on a current loop
- magnetic moment of a loop, N turns area A
- torque in a uniform field
- potential energy of the loop
- Where the coil rests
- Moving coil galvanometer
- Converting a galvanometer
- To an ammeter
- To a voltmeter
- Crossed fields: the velocity selector
- The cyclotron
- The mass spectrometer
- The Hall effect
- Symbols
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Physics chapter by chapter against your real exam dates and free hours, and when the plan reaches Moving Charges and Magnetism the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.