lesson 3 physics 10adv

• Resistance is the opposition presented to electric current by a material or device
• Ohm’s law states that current passing through a wire is directly proportional to the potential difference between its terminals
• The SI units for measuring the resistance of a conductor is the Ohm (Ω)
• Resistors can be connected in series or in parallel
• Resistors can be connected together in an unlimited number of series and parallel combinations to form complex resistive circuits
• A Series Circuit describes two or more components of a circuit that provide a single path for current
• Resistors in Series carry the same current
• The equivalent resistance in a series circuit is the sum of the circuit’s resistances
• Two or more resistors in the actual circuit have the same effect on the current as one equivalent resistor
• The total current in a series circuit equals the potential difference divided by the equivalent resistance
• One bulb burning out in a series circuit breaks the circuit
• In parallel circuits, each bulb has its own circuit, so all but one bulb could be burned out, and the last one will still function
• A voltage divider is a simple circuit that turns a large voltage into a smaller one
• A voltage divider produces a source of potential difference that is less than the potential difference across the battery
• A photoresistor’s resistance depends on the amount of light that strikes it
• A photoresistor is sensitive to light. Its resistance decreases when lighting increases
• Voltage dividers are often used with sensors, such as Photoresistors
• In this device, an electronic circuit detects the potential difference and converts it to a measurement of illuminance that can be read on the digital display
• Light meters used in photography use a voltage divider. The amount of light striking the photoresistor sensor determines the voltage output of the voltage divider
• For a circuit with a 22 Ω and a 33 Ω resistor connected in series across a 120 V potential difference:

  • The equivalent resistance of the circuit is 55 Ω
  • The current in the circuit can be calculated using Ohm's Law
• For three resistors of 3.3 kΩ, 4.7 kΩ, and 3.9 kΩ connected in series across a 12 V battery:

  • The equivalent resistance of the circuit needs to be calculated
  • The current through the resistors can be determined
• Resistors in Parallel:

  • Components in a parallel circuit provide separate conducting paths for current
  • Parallel circuits do not require all elements to conduct
• Equivalent Resistance for Resistors in Parallel:

  • The total current in parallel resistors equals the sum of individual currents
  • The potential energy loss is the same across all parallel resistors
• For a circuit with four resistors in parallel:

  • Calculate the equivalent resistance for the circuit
  • Determine the total current in the circuit
• For three 15.0 Ω resistors connected in parallel across a 30.0 V battery:

  • Find the equivalent resistance of the parallel circuit
  • Calculate the current through the entire circuit
  • Determine the current through each branch of the circuit
• If one 15.0 Ω resistor is replaced by a 10.0 Ω resistor in the previous problem:

  • The equivalent resistance changes
  • The current through the entire circuit changes
  • The current through the other 15.0 Ω resistors remains the same
• For a circuit with a 120.0 Ω, 60.0 Ω, and 40.0 Ω resistor connected in parallel across a 12.0 V battery:

  • Calculate the equivalent resistance of the parallel circuit
  • Determine the current through the entire circuit
  • Find the current through each branch of the circuit
• Kirchhoff's Rules:

  • Kirchhoff formulated two rules for electric circuits: the loop rule and the junction rule
  • The loop rule is based on the law of conservation of energy
  • The junction rule is based on the law of conservation of charge
• The Loop Rule:

  • The sum of voltage differences around a loop in an electric circuit must be zero
• The Junction Rule:

  • The total current into a section of an electric circuit equals the total current out of that section
• For a series circuit with a switch and a 75 W bulb connected to a 120 V source:

  • The potential difference across the switch when closed is 0 V
  • Adding another 75 W bulb in series results in 0 V potential difference across the switch
• For a series circuit with four resistors and a known current through one resistor:

  • Calculate the total current supplied by the source
• For a parallel circuit with four branch currents:

  • Determine the total current supplied by the source