Electricity and Electromagnetism L2

Electric Field Strength (E)

The force per unit charge experienced by a positive charge. E=V/d​. The unit is V/m or Vm−1.

Force on a Charge (F) in a Field

Calculated by F=Eq

Electric Potential Energy Change (ΔEp​)

The work done on a charge moving in an electric field. ΔEp​=Eqd.

Movement of Charges in E field

Negative charges (like electrons or beta particles) move towards the positive plate. Positive charges (like alpha particles) move towards the negative plate.

Energy Conversion

As charges move in an E field, electrical potential energy is converted to kinetic energy (Ek​=21​mv2).

Lightning/Shocks

Caused by a buildup of charge. Grounding (earthing) provides a path for charge to flow to prevent sparks.

Current (I)

A movement of charge. I=q/t​.

Conventional Current

Flows from positive to negative, which is opposite to the direction of electrons.

Voltage (V) / Electric Potential

V=ΔE/q​. 1 volt=1 joule/1 coulomb.

Ohm's Law

The relationship linking voltage, current, and resistance: V=IR.

Ohmic Conductor

Has the same resistance (e.g., a resistor at constant temperature); V vs. I graph is linear.

Non-Ohmic Conductor

Has changing resistance (e.g., diodes, LDRs); V vs. I graph is non-linear

Series Circuit Rules

Current is the same at all places. Voltage is shared; sum of component voltages equals supply voltage.

Parallel Circuit Rules

Voltage across components is the same for each. Current splits; the sum of currents in branches equals the current before the split.

Resistors in Series (RT​)

RT​=R1​+R2​

Resistors in Parallel (RT​)

RT​1​=R1​/1​+R2​/1​​

Power (P) (Rate of Energy Transfer)

P=ΔE/t

Electrical Power (P) Dissipated

P=IV, P=I²R

P=V²/R

Magnetic Field Lines Direction

By convention, lines go from North (N) to South (S) poles outside the magnet.

Force on a Current-Carrying Conductor

Calculated by F=BIL. (Motor Effect)

Force on a Moving Charged Particle

Calculated by F=Bqv

Direction of Force (Fleming's Left Hand Rule)

Used to find the direction of the force/motion when current flows in a magnetic field : Thumb: Motion (Force) Index Finger: Field * Middle Finger: Current

Induced Voltage (EMF) across Conductor

Generated across a straight conductor moving in a uniform magnetic field: V=BvL. (Electromagnetic Induction)

Drawing Magnetic Fields (Convention)

Into the page/paper: X. * Out of the page/paper: dot (or circle with a dot)