SPH3U Grade 11 Physics Electricity and Magnetism Test

Electricity Unit Test Study Notes

  • Electrostatics
    • Static Electricity: build up of stationary electric charge on a substance
    • Fundamental Laws of electric charges: likes repel, opposites attract
    • Charging: to create an imbalance of electric charges on either substance
      • Charging by Friction: rubbing rips out the electrons and charging it
      • Charging by Contact: touching will affect the movement of the charges
      • Charging by Induction: the electric fields can move the charges in the object.
    • Electric Charges
      • Coulomb’s Law: the magnitude of force between 2 charged particles are directly proportional to product of charges and are inversely proportional to the distance squared
      • F = kQ1Q2/D^2
      • F is Force, K is 9e9
    • Calculating Electric Charges
      • Relationship between number of electrons and charge
      • Q=Ne
      • N is number of electrons, e is a constant of elementary charge 1.60*10^-19
    • Electric Current
      • Defined as the rate of movement of electrically charged particles past a point
      • Flows from Positive to negative (long side to short side of terminal)
      • Cathode to Anode
      • I = Q/delta T
      • Q is Coulombs, I is current, T is time in seconds
      • 1A = 1C/s
    • Electric Potential difference
      • V = w/q
      • Amount of work it takes to move a certain amount of charge of electricity
      • 1V = 1J/C
    • Kirchoff’s Law of electric circuits
      • Law of conservational charge: electric charge is neither lost or accumulate at any point in a circuit
      • Kirchoff’s Voltage Law: around any complete path, the sum of voltage increases is equal to the sum of decreased in electric potential
      • Kirchoff’s Current Law: At any junction in an electric circuit, the total electric current into the junction is equal to the total electric current out
      • Solving Circuit Equations:
        • Parallel
          • V0 = V1 = V2 = V3..= VN
          • I0 = I1 + I2 + I3.. + IN
          • 1/R0 = 1/R1 + 1/R2 + 1/R3.. + 1/RN
        • Series
          • V0 = V1 + V2 + V3.. + VN
          • I0 = I1 = I2 = I3… = IN
          • R0 = R1 + R2 + R3.. + RN
    • Electrical Resistance
      • The amount of impedance something has against a current in a circuit
      • Ohm’s Law
      • Unifies voltage, current, and resistance
        • V = I*R
    • Electric Power
      • Measured in Watts, is how much energy is consumed / time
      • P = I * V
      • Using Ohm’s Law, I or V can be substituted with their equivalence.
      • When paying, it’s measured in Kilowatt Hours, instead of watts per second
  • Electromagnetism
    • Laws of Magnetic forces
      • Opposites attract, like repel
      • Magnetic fields always travel from the North side to the south
    • Magnetic Materials
      • Domain Theory
        • In magnetic materials, it is said that there are small polar dipoles grouped into domains
        • these domains will move and attract to eachother, forming the material
        • The orientation of these dipoles can also be affected by nearby magnets as well
      • Permanent Magnets: magnets where the dipoles are in a fixed position to define their poles
      • Ferromagnets: magnets with random ordered dipoles until they are affected by permanent magnets nearby.
      • Magnetic Induction: the process of altering the order of the dipoles by adjusting their positions and having it temporarily stable
      • Demagnetization: Magnets which’ve lost their direction of dipoles
      • Reverse Magnetization: If strong magnets are placed near an end of a magnet, it has the potential to switch poles and reversed
      • Magnetic Saturation: when the strength of the magnet has increased to it’s maximum and become saturated.
    • Magnets from electric current
      • a straight conductor carrying a current creates a magnetic field around it
      • 1st Right hand rule
        • Thumb points in direction of current
        • Fingers, in direction it’s pointing, indicates direction of magnetic field
      • (X) indicates current inside page, (.) indicates current coming out
    • Magnetic Field from a solenoid
      • a coil of wire, coiled up, can create an magnetic field in the ends with current
      • 2nd Right hand rule
        • Thumb indicates direction of magnetic field
        • Fingers point in direction of current flowing in the solenoid
      • Factors that affect magnetic field of coil:
        • Current in coil, more coil is directly proportional to it
        • Number of loops, also directly proportional
        • Type of core material: different materials have different Magnetic permeability
      • Magnetic Permeability relative: the factor by which a core material increases the magnetic field strength
      • Ferromagnets: usually have high K as they help increase magnetic field strength
      • Paramagnetic: materials that only magnetize slightly (air, aluminum)
      • Diamagnetic: materials that reduces magnetic field of the coil (copper, water)
      • Electromagnetic Relay: using a soft iron core called an Armature, the first circuit’s electromagnet will lift or lower the armature thus, enabling and disabling the second circuit
    • Motor Principles
      • With magnetic fields created by an electric current, there can be movement or force obtained by the wire
      • Using third right hand rule, we can find that out
        • thumb points in the direction of the current
        • fingers point in direction of magnetic fields
        • palm points out in direction of the force acting on it
      • 2 wires side by side will have their own movements too based on 1st right hand rule
    • Motors
      • Using a solenoid and 2 permanent magnets on each side, the current can be used to move the solenoid
      • When it switches over to the other side, the current’s direction is flipped in reverse, allowing the same attraction to the incoming magnet
  • Electromagnetic induction
    • Law of Electromagnetic induction: from Faraday
      • An electric current induced in a conductor whenever the magnetic field in the region of the conductor changes
    • Lenz’s law of induced current
      • when a magnet is placed closer to a coil, the coil can create a current
      • And in creating a current, it will also create it’s own field
      • According to Lenz, that field will always be opposite to that pointing towards it
      • Therefore, to figure out direction of current, right hand rule, with thumb pointing north, will work
    • When looking at current based on the direction wire is moving, use third right hand rule, and it’s the opposite direction of current as the right hand rule suggests.
    • If direction is given, current will be opposite of what right hand rule suggests.
  • More random stuff with Electricity and magnets
    • Transformers
      • Based on Faraday’s ring’s theory, a Transformer can be used to Up or lower the voltage in a current of electricity
      • Because magnetic fields are created by solenoids, that field can carry itself to other solenoids through an iron ring
      • In ratio to the number of windings in the primary and secondary solenoid, a transformer can up scale or down scale a voltage accordingly.
      • Step down Transformer has lesser secondary windings
      • Step up Transformer has more secondary windings