Electric Circuits

Notes

The following topics are covered in this chapter.

• Ohm's Law
  • Define potential difference as the work done per unit positive charge $V=\frac{W}{q}$ 
  • Define current as the rate of flow of charge $I=qt$ 
  • Determine the relationship between current and potential difference at constant temperature
  • State Ohm's Law: Current through a conductor is directly proportional to the potential difference across the conductor at constant temperature
  • Distinguish between Ohmic and non-Ohmic conductors
  • Define resistance as a material's opposition to the flow of electric current
  • State that the unit of resistance is the ohm
  • Calculate the effective resistance of resistors in series using $R_T=R_1+R_2$
  • Calculate the effective resistance of resistors in parallel using
  • Interpret circuit diagrams containing a source, switches, resistors, ammeters and voltmeters
  • Solve problems using the mathematical expression of Ohm's Law $R=\frac{V}{I}$  for series and parallel circuits, limited to a maximum of three external resistors
• 2. Power and Energy
  • Solve problems using electrical energy $W=Pt$
  • State that electrical energy is measured in joules (J)
  • Know that electrical power dissipated in a device is equal to the product of the potential difference across the device and current flowing through it
  • Solve problems using $P=VI$ or $P=I^{2}R$ or $p=\frac{V^2}{R}$
  • Solve problems using $W=VIt$ or $W=I^{2}Rt$ or $W=\frac{V^2}{R}t$
  • Know that the kilowatt hour (kWh) is a unit of energy and that 1 kWh is the amount of energy used when 1 kilowatt of electricity is used for 1 hour
  • Calculate the cost of electricity usage given the power specifications of the appliances used as well as the duration if the cost of 1 kWh is given
• 3. Internal Resistance and Series and Parallel Networks
  • Solve problems involving current, voltage and resistance for circuits containing arrangements of resistors in series and in parallel for a maximum of three external resistors
  • State that a real battery has internal resistance
  • Define emf as the total energy supplied per coulomb of charge by the cell
  • The sum of the voltages across the external circuit plus the voltage across the internal resistance is equal to the emf: $emf=V_{load}+V_{internalresistance}$ or $emf=I{R}_{ext}+Ir$
  • Solve circuit problems in which the internal resistance of the battery must be considered
  • Solve circuit problems, with internal resistance, involving seriesparallel networks of resistors to a maximum of three external resistors