DC Circuits

• The Law of Conservation of Charge states that charges cannot be created nor destroyed. Thus, the total charge that enters a junction is equal to the total charge leaving it per unit time.
• Current Law states that the sum of currents entering any junction in an electric circuit is always equal to the sum of currents leaving that junction.
• Since the Principle of Conservation of Energy states that energy cannot be created nor destroyed, the electrical energy produced by the source should be equal to the sum of electrical energy consumed by all the components.
• Voltage Law states that in any closed loop in an electric circuit, the total electromotive force supplied equals to the total potential difference in that loop.
• In a series circuit, the combined resistance of resistors in series is always larger than the largest resistance in the network.

  $R_s =$$R_1 +$$R_2 +$$...$
• In a parallel circuit, the combined resistance of resistors in parallel is always smaller than the smallest resistance in the network.

  $\frac{1}{R_p}=$$\frac{1}{R_1}+$$\frac{1}{R_2}+$$...$
• A potential divider is an arrangement of resistors which is used to obtain a fraction of the potential difference provided by a voltage supply.
• $I =$$I_1+$$I_2+$$...$

  Only occurs when components are placed in parallel configuration.
• $V =$$V_1+$$V_2+$$...$

  Only occurs when components are placed in series configuration.
• $V=$$(\frac{R_1}{R_1+R_2})E$ (in name)


  V = Fraction of the Voltage of the Supply

  $R_1$ = Resistance of Resistor 1

  $R_2$ = Resistance of Resistor 2

  E = Electromotive Force
• Potential is present at every point of a circuit. Two points have the same potential if they are connected directly by a wire of zero resistance, while two points would have different potentials if they are separated by a component with resistance.
• Ideally, Voltmeters:

  • Have infinite internal resistances
  • Do not draw current from the circuit
  • Read the theoretical potential difference between two points
• Realistically, Voltmeters:

  • Have finite internal resistances
  • Draws small current from the circuit
  • Read a potential difference smaller than the theoretical value
• Ideally, Ammeters:

  • Have no internal resistances
  • Have no potential difference across its ends
  • Read the theoretical current in the path
• Realistically, Ammeters:

  • Have small internal resistances
  • Have finite potential difference across its ends
  • Read a current that is smaller than the theoretical value
• A thermistor is a resistor whose resistance varies greatly with temperature. Its resistance decreases with increasing temperature.
• An Light Dependent Resistor (LDR) is a resistor whose resistance varies with the intensity of light falling on it. Its resistance decreases with increasing light intensity.
• A potentiometer is a variable resistor that can be used to control the current in a circuit. When the sliding contact is at a point where current in the circuit is zero (as seen from null reading of a galvanometer), this point is known as the balance length.
• Input the correct terms:

  A) Electromotive

  B) Force

  C) Battery

  D) Internal

  E) Resistance

  F) Cell

  G) Resistance

  H) Two