Basics

• Terms table

  
• standard form

  
• If two variables are proportional, when one halves, so does the other. When one triples, so does the other.

  
  

  If two variables are inversely proportional, when one halves, the other doubles. When one triples, the other is divided by three
• V = IR if voltage increased and resistance stayed fixed, -> current increases as voltage increases because voltage and current are proportional, and resistance stays fixed.
• Current

  Current measures how much charge goes past a point in one second.

  Electrons have charge so moving electron forms current. Current can be made of anything that has charge.

  
  

  Has symbol I measured in Amps A. If Q is the charge (in coulombs C) passing a point in a circuit in time then: I = Q/t

  
  

  Current is the same every where in series circuits but have different values in different branches in parallel circuits.
• Conventional current

  Current has direction. conventional current states current goes from positive to negative terminal but really it goes from negative to positive.

  
• Voltage


  Symbol V, measured in V for volts. It’s the energy change of an electron.

  
  

  Positive voltage across a component means electrons are gaining energy. ∆E = Ef − Ei. Positive because Ef is greater than Ei.

  
  

  Negative voltage across a component means that the electrons are losing energy.

  ∆E = Ef − Ei. Negative because Ef is smaller than Ei.

  
  

  Formulas: V = ∆E / q

  ∆E = V x q
• Ohm's law

  Compare the voltage across a component (the pull on the electrons) with the current through that component (the flow of the electrons), they are quite similar. The difference between these two values is the resistance of the component, symbol R measured in Ω (ohms).

  
  

  Equation: V = IR
• Series and parallel resistors

  Formulae:

  Series: RT = R1 + R2 + ...

  Parallel: 1/RT = 1/R1 +1/R2 + ..
• Power

  Amount of energy that a circuit component transforms every second

  
  

  Equation:

  From P∆E/t to P=IV -> P = ∆E/t = (Vq)/t = V x q/t = VI