9 - Electrical Circuits

• What is an electric circuit?

  A path for electric charge to flow
• What are the requirements for an electrical circuit to work?

  • A source of energy
  • A complete loop
  • A component
  • No short circuits
• What does a resistor do in a circuit?

  Limits current flow in one direction
• What is potential difference also called?

  Voltage
• How is voltage measured?

  In volts (V) using a voltmeter
• How must a voltmeter be connected in a circuit?

  In parallel
• What does a 1V cell provide to each coulomb of charge?

  1 joule (J) of energy
• What produces a potential difference across a cell?

  A chemical reaction inside the cell
• What is a battery made of?

  Two or more cells joined together
• How is the potential difference across a battery calculated?

  Sum of the p.d. across the cells
• How many cells are in a 12V car battery?

  6 cells of 2V each
• What is current a measure of?

  Rate of flow of electric charge
• How is electric charge measured?

  In coulombs
• How is current measured?

  In amperes (A) using an ammeter
• What does a current of 1A represent?

  1 coulomb of charge flowing every second
• How must an ammeter be connected in a circuit?

  In series
• In which direction does current flow in a circuit?

  From positive terminal to negative terminal
• What is the direction of conventional current?

  From + to - terminals
• What carries electric charge in a circuit?

  Electrons
• What is the current behavior in a series circuit?

  • The current is the same in every part
• What is the current behavior in a parallel circuit?

  • The current is different in different branches
• What is the relationship between current and voltage for a fixed resistor?

  Directly proportional relationship
• What does Ohm's Law state?

  Resistance is constant and doesn't depend on current
• What do diodes do in a circuit?

  Allow current to flow in one direction
• What are thermistors and how do they work?

  • Type of resistor
  • Resistance depends on temperature
  • Resistance decreases as temperature increases
• What are LDRs and how do they work?

  • Type of resistor
  • Resistance depends on light intensity
  • Resistance decreases as brightness increases
• What is the resistance of a thermistor at 20°C?

  560 Ω
• What is the resistance of a thermistor at 37°C?

  470 Ω
• What is the resistance of a thermistor at 56°C?

  340 Ω
• What is the resistance of an LDR at low light intensity?

  1763 Ω
• What is the resistance of an LDR at medium light intensity?

  1184 Ω
• What is the resistance of an LDR at high light intensity?

  476 Ω
• How do you calculate total resistance in series resistors?

  • Total resistance is the sum of each resistor
  • Example: 5 + 10 = 15 Ω
• How do you calculate total resistance in parallel resistors?

  • Total resistance is less than the smallest resistor
  • Example: 5 + 10 = 0.61 Ω
• What is the total resistance of two resistors in series with values 5Ω and 10Ω?

  15 Ω
• What is the total resistance of two resistors in parallel with values 5Ω and 10Ω?

  0.61 Ω
• What is the total resistance of three resistors in series with values 5Ω, 10Ω, and 15Ω?

  30 Ω
• What is the total resistance of three resistors in parallel with values 5Ω, 10Ω, and 15Ω?

  0.44 Ω
• How is resistance measured?

  • Measured using an ohmmeter
  • Can be done with a multimeter
• What is the total resistance of two resistors in series with values 5Ω and 15Ω?

  20 Ω