capacitor

• What is the symbol for a capacitor?

  Two parallel lines
• What is the primary function of a capacitor?

  To store electrical charge
• How is the charge stored on a capacitor related to potential difference?

  Charge is proportional to potential difference
• What is the formula for capacitance?

  $c =$$\frac{q}{v}$
• What does capacitance measure?

  Charge stored per unit of potential difference
• What is the unit of capacitance?

  Farad
• How is one farad defined?

  One coulomb stored for one volt
• Describe the flow of electrons when charging a capacitor.

  Electrons flow from negative terminal to negative plate
• What happens to the charges on the plates of a capacitor during charging?

  Plates acquire equal and opposite charges
• How can a charged capacitor be used in a circuit?

  As a power source for devices
• What is the rule for adding capacitors in parallel?

  • Total capacitance is the sum of individual capacitances:
  • $C_{total} =$$C_1 +$$C_2$
• What is the total capacitance of two 300 microfarads capacitors in parallel?

  600 microfarads
• What is the rule for adding capacitors in series?

  • Total capacitance is given by:
  • $\frac{1}{C_{total}} =$$\frac{1}{C_1} +$$\frac{1}{C_2}$
• What is the total capacitance of two 300 microfarads capacitors in series?

  150 microfarads
• Why are the rules for adding capacitors opposite to those for resistors?

  Capacitors store charge, resistors dissipate energy
• What are the characteristics of capacitors in a parallel circuit?

  • Same potential difference across all branches
  • Total charge is shared among capacitors
  • $Q_{total} =$$Q_1 +$$Q_2$
• What are the characteristics of capacitors in a series circuit?

  • Same current through each capacitor
  • Total charge is the same for all capacitors
  • $V_{total} =$$V_1 +$$V_2$
• What happens to the voltage across a capacitor during discharging?

  It decreases exponentially
• What is the equation for voltage across a discharging capacitor?

  $V =$$V_0 e^{-\frac{t}{CR}}$
• How do you calculate the charge on a discharging capacitor?

  $Q =$$Q_0 e^{-\frac{t}{CR}}$
• What is the current equation during capacitor discharge?

  $I =$$I_0 e^{-\frac{t}{CR}}$
• How do you find the voltage across a capacitor after 150 seconds of discharging?

  Use $V =$$V_0 e^{-\frac{t}{CR}}$
• What is the initial voltage of a 500 microfarad capacitor charged to 6 volts?

  6 volts
• What is the voltage across a 500 microfarad capacitor after 150 seconds discharging through a 500 kilo-ohm resistor?

  3.29 volts
• What defines an exponential function in terms of decay?

  • Constant ratio of decrease in equal time intervals
  • Example: Decrease by a factor of a third
• How do you rearrange the voltage equation for time?

  $t =$$CR \ln\left(\frac{V_0}{V}\right)$
• What is the time constant in a capacitor circuit?

  • Defined as $\tau =$$CR$
  • Determines charging and discharging rates
• What happens at the time equal to the time constant?

  Voltage drops to 37% of original value
• How can you determine capacitance from a graph of voltage against time?

  Use time constant and resistance
• What is the relationship between voltage across a charging capacitor and the voltage across a resistor?

  Voltage across capacitor increases, resistor decreases
• What is the formula for the voltage across a charging capacitor?

  $V_C =$$V_0(1 - e^{-\frac{t}{CR}})$
• How do you express the charge across a charging capacitor?

  $Q_C =$$Q_0(1 - e^{-\frac{t}{CR}})$
• How does current behave in a charging circuit?

  Current decreases as capacitor charges
• What happens to current when the capacitor is fully charged?

  Current drops to zero