Electricity

• Series circuit

  There is only one path/loop
• Parallel circuit

  There is more than one path/loop
• An ammeter is connected in series with a component to measure the current, in amps, in the component.
• A voltmeter, used to measure voltage, is always placed in parallel.
• In a series circuit, current is the same everywhere.
• In a series circuit, components share the voltage between them.
• The more components in a circuit, the lower the current (for the same voltage).
• In a parallel circuit, current is conserved at a junction in a circuit.
• In a parallel circuit, voltage is the same on each branch.
• Lights and LEDs (light emitting diodes) can be used to estimate the current flowing through a circuit:

  • Bright light = high current
  • Dim light = lower current
• If a component is disconnected from a:

  • series circuit, the circuit is said to have been broken - it stops working.
  • parallel circuit, current flows down a different path - it keeps working.
• Electric current is the rate of flow of charge. In metals, current is a flow of electrons.

  (Rate of = amount per second)
• Charge = current x time

  Q = It
• Q stands for quantity of charge
• I stands for intensity of current
• Voltage is sometimes called potential difference
• Voltage Is the energy difference of a charge between two points. Therefore, 1 volt = 1 Joule per 1 Coulomb.
• Energy transferred = charge moved x voltage

  E = QV
• Resistance is a measure of how much a component tries to stop current passing through it.
• Resistance increases: current decreases
• A variable resistor is used to vary the current in a circuit.
• Voltage = current x resistance

  V = IR
• Voltage drives the current. The higher the voltage, the higher the current.
• All components have a resistance, the more components, and higher the resistance, the lower the current.
• In order to test or measure the resistance of a component you must have:

  1. A component (e.g. lamp or resistor)
  2. A way of measuring current
  3. A way of measuring voltage
  4. A way of varying the current
• When resistors are in series, the total resistance of the circuit is increased because the pathway becomes harder for current to flow through.
• When resistors are in parallel, the total resistance is less than the resistance of the individual resistors. This is because there are more paths for the current.
• Resistance: A measure of the opposition to the flow of current.
• Current: The rate of flow of charge, measured in amps, A
• Voltage: The energy transferred per unit charge, measured in Joules/coulomb called Volts, V.
• Potential divider: A simple circuit arranged that divides the voltage across two or more components.
• Ohmic: A substance that obeys Ohm’s law.
• Non-ohmic: A substance that does not obey Ohm’s law
• Quadrant: Graphs can be divided into four quadrants, including positive x and y axes, negative x and y axes, positive x axis and negative y axis, and positive y axis and negative x axis
• Sometimes, components have fixed resistances, but for the other components the resistance will vary depending on temperature or another stimulus.
• To calculate the resistance of an electrical component, measurements of the current through the device and voltage across the components are needed.
• If a component obeys V = IR (at constant temperature) then it is considered to be ohmic. If it does not obey this equation then it is non-ohmic.
• A resistor at a constant temperature: Resistance is constant.
• Filament lamp: Resistance is highest at high voltage, because of high temperature
• Diode: Resistance is infinite when negative. Only allows current in one direction.