Electricity & Magnetism

Electricity & Magnetism

1. Static Electricity

   • Electric Charge
     • Law of Charges
       • unlike charges attract; like charges repel
     • Electrons
       • -1.6*10^-19 C
   • Electric Field
     • magnitude of electric field: force per unit charge. (N/C) E = F/q  E= kq2/r^2 (from coulomb's law)
   • Coulomb's Law
     • magnitude of electric force (attraction or repulsion between charged particles); kind of like Fg F(electric) = (kq1q2)/r^2k = 9 *10^9
   • Potential Difference
     • the work required to move charge q between two points in electric field. (voltage) ΔV = work/q

2. Current & Circuits

   • Types of Circuits
     • Parallel
       • two or more resistors, where current has more than one path, with same voltage in each resistors. (inverse resistance)
     • Series
       • two or more resistors with the same current passing through each. 
   • Capacitors
     • two conducting plates connected to a battery; one is negative, one is positive. capacitance of plates (C) = Q/V  change in charge (ΔQ) = IΔt
   • Components of Circuit
     • Power
       • the rate at which work is done or energy is transferred in a circuit! P = IVP = I^2RP = V^2/R
     • Heat
       • Joule's Law of Heating an amount of heat is produced whenever energy flows through a resistor. H = I^2Rt
     • Voltage
       • the potential difference (work per unit charge); moves across terminals of a battery
     • Current
       • the amount of charge moving through conductor per second (charge per second) 
     • Resistance
       • the opposition to the flow of charges (ohm); kind of like a friction through conductors. 

3. Magnetism

   • Electromagnetism
     • the relationship between electricity and magnetism
     • Electromagnetic Induction
       • process through which an electric current can be induced by a changing magnetic field
       • electromotive force
         • the voltage that is generated by a magnetic force (not a force, but represents energy/unit charge) emf = LvB
   • Magnets
     • north pole and south pole, like law of charges. cannot be isolated;
   • Magnetic Field
     • the field is around magnets; magnitude is greatest near the poles & decreases with increasing distance
     • Right-Hand Rule #1
       • find the direction of magnetic field! wire: held in right hand current direction: thumb magnetic field: fingers curl
   • Magnetic Domains
     • explains magnetic properties of materials. domains are formed by large groups of atoms with net spins. once placed in magnetic field, some domains may become aligned. the more domains become aligned, the stronger the magnetic field.
   • Magnetic Force
     • for charge in B
       • a charge particle moving through magnetic field experiences magnetic force. max when charge is moving perpendicular; zero when particle moves along field lines (tesla) F(magnetic) = qvB 
       • Right-Hand Rule #2
         • find direction of magnetic force on positive charge magnetic field: fingers velocity: thumb magnetic force: palm of hand
     • for current carrying wire
       • a wire with current experiences a magnetic force. F(magnetic) = BIL(sinΘ)  Θ = angle between wired and magnetic field
       • Solenoid
         • series of closely spaced coils of wire; depends on current in wire and number of coils; strength increases by inserting an iron rod into center (electromagnet)
   • Devices
     • Generator
       • a device that transforms mechanical into electrical energy. 
     • Motor
       • reverse of generator: electrical energy transforms into mechanical energy.