Electromagnetism and Capacitors Study Notes

Electromagnetism Rules

  • Screw Rule: Indicates the direction of current flow and magnetic field; screw moves in the direction of the magnetic field when turned in the direction of current.

  • Grip Rule: Aligns fingers of the right hand in current direction; thumb points in magnetic field direction.

  • Fleming's Left-Hand Rule: For motors, fingers represent direction of force (thumb), magnetic field (index), and current (middle).

Factors Affecting Force on Current-Carrying Conductor

  • Strength of the magnetic field

  • Magnitude of the current

  • Length of the conductor in the field

  • Angle between the conductor and the magnetic field direction

Magnetic Fields Formed by Current

  • Current Away from Viewer: Circular magnetic field lines formed in counterclockwise direction (right-hand grip rule).

  • Current Towards Viewer: Circular magnetic field lines formed in clockwise direction (right-hand grip rule).

Capacitors

  • Plate vs Dielectric: Plate is the conductive surface, while dielectric is the insulating material between plates that affects capacitance.

Applications of Capacitors

  • Energy storage in power supplies

  • Smoothing out voltage fluctuations in electronic circuits

Energy Stored in a Capacitor

  • Expression Derivation:

    1. Charge on a capacitor: Q=CVQ = CV

    2. Energy stored: U=12QV=12CV2U = \frac{1}{2} QV = \frac{1}{2} CV^2

Capacitance Calculation

  • Dimensions: Two plates 40 cm x 40 cm, separation 6 mm; glass (5 mm thick) permittivity 8, paper (1 mm thick) permittivity 2.

  • Capacitance Formula: C=εAdC = \frac{\varepsilon A}{d} where (\varepsilon) is the permittivity, (A) is the area, and (d) is the separation.

Energy Stored in Capacitor Calculation

  • Given: p.d of 10kV applied.

  • Energy Stored Formula: Using the above formula for energy with found capacitance.