Physics - Electricity

• Proton: an atom with a positive electric charge
• Neutron: an atom that is uncharged
• Electron: an atom with a negative charge
• An atom is uncharged because it has the same number of protons and electrons.
• Electric current is the rate of flow of charge and is measured in amps (A), using the symbol I and is measured with an ammeter.
• Voltage/Potential Difference is the energy that is transferred per unit of charge flowing through a component.
• The voltage's unit is V, the symbol is V, and it is measured with a voltmeter
• The voltmeter has to be placed parallel to the circuit and the potential difference is the same throughout.
• Ohms law is the current through a component directly proportional to the voltage across it at a constant temperature
• Resistance is the opposition to the flow of charge in a circuit, and it's unit is ohms (Ω), and the symbol is R
• Parallel circuits have multiple paths for electricity to travel along, meaning that if one part of the circuit fails, other parts still work.
• Series circuits have only one pathway for electricity to travel around them, so if any part of the circuit breaks down then no power will reach the bulb or appliance.
• Formula: V = IR

  aka: P.D. = Current * Resistance
• Directly proportionate = straight line through 0% and 100%
• At a junction in a circuit, the current into the junction is equal to the sum of the current at the junction.
• A1 = A2 = A3

  Same current flowing throughout.
• V = V1 + V2
• The direction of electron flow is opposite to the direction of conventional current flow.
• Parallel circuits are those with more than one loop and generally each loop will only contain a single component
• Parallel circuits are much more useful than series circuits because if any particular component breaks, the overall circuit is still intact
• Circuits can be a mix of series and parallel parts
• In truly parallel circuits with only one component in each loop, all components get their full source potential difference
• In truly parallel circuits, the current is shared between all of the loops
• The total current in a parallel circuit is the sum of the currents in each loop
• Current splits in parallel circuits


  The way the current splits will depend on the resistance of the individual components, with loops of greater resistance taking a lower share of the current
• Current in parallel circuits analogy

  Current is like water flowing down a hill, taking the path of least resistance
• In parallel circuits, the more components added in parallel, the lower the total resistance of the circuit will be
• Adding more components in parallel decreases total resistance


  It's like adding more possible routes for water to flow down a hill, making it easier for the water to flow, thus decreasing overall resistance
• The more loops added in parallel, the lower the overall resistance will be, even if those loops contain big resistors
• Charge: a fundamental property of matter, and it is measured in coulombs (C).
• Example question: A resistor of 20 Ω is measured to have 2 A of current flowing through it. What is the P.D. measured across the resistor?

  I = 2 A

  R = 20 Ω

  Voltage = Current * Resistance

  V = 2 * 20 = 40 V
• Series Circuit Rules:

  1. Current in a series circuit has the same value throughout the circuit
  2. The total resistance is the sum of all the individual resistances of the components in a circuit.
  3. The total P.D. is shared by all the components.
  4. A component with more resistance, takes a bigger share of the P.D.
• Parallel Circuit Rules:

  1. Adding more branches to a circuit always lowers the total resistance.
  2. Total Current going into a junction = Total current going out of a junction.
  3. In Parallel Circuits, branches with higher resistance receive less current compared to branches with lower resistance.