Current and circuit

• What is current in an electrical circuit?

  Current is the flow of electrical charge.
• What does the total charge through a circuit depend on?

  The total charge depends on current and time.
• What are the circuit diagram symbols that need to be learned?

  • Resistor
  • Fuse
  • Battery
  • Switch
  • Bulb
• How long does a laptop charger need to be connected to transfer 28,800 C of charge at a current of 8 A?

  It needs to be connected for 360 minutes.
• What components are included in a simple circuit created by a student?

  A battery, a switch, and a bulb.
• What is the formula linking potential difference and current?

  • Potential difference (V) = Current (A) × Resistance (Ω)
• What is the current through a 40 Ω resistor with a potential difference of 6.0 V across it?

  The current is 0.15 A.
• What factors can affect the resistance of a circuit?

  • Whether components are in series or parallel
  • Length of wire used in the circuit
• What does an ammeter measure?

  An ammeter measures the current flowing through the test wire.
• How must an ammeter be placed in a circuit?

  An ammeter must always be placed in series with whatever you're investigating.
• What does a voltmeter measure?

  A voltmeter measures the potential difference across the test wire.
• How must a voltmeter be placed in a circuit?

  A voltmeter must always be placed in parallel around whatever you're investigating.
• What is the procedure for investigating resistance using wire length?

  1. Attach crocodile clips to the wire at specified lengths.
  2. Close the switch and record current and potential difference.
  3. Open the switch, adjust clips, and repeat.
  4. Calculate resistance using R = V ÷ I.
  5. Plot resistance against wire length.
• What does a straight line through the origin on a resistance vs. length graph indicate?

  It indicates that resistance is directly proportional to length.
• What could cause a graph of resistance not to go through the origin?

  A systematic error in measuring the length of the wire could cause this.
• What is the resistance of an appliance connected to a 230 V source with a current of 5.0 A flowing through it?

  The resistance is 46 Ω.
• What characterizes ohmic conductors?

  Ohmic conductors have a constant resistance.
• What does the term "I-V characteristic" refer to?

  It refers to a graph showing how current changes as potential difference increases.
• How do non-ohmic components differ in their I-V characteristics?

  Non-ohmic components have I-V characteristics that are not straight lines.
• What is the shape of the filament lamp I-V characteristic in the positive quadrant?

  The shape is curved, indicating changing resistance with current.
• What is an LDR?

  An LDR is a resistor that depends on the intensity of light.
• How does the resistance of an LDR change with light intensity?

  In bright light, the resistance is low; in darkness, the resistance is high.
• What are some applications of LDRs?

  They are used in automatic night lights, outdoor lighting, and burglar detectors.
• What is a thermistor?

  A thermistor is a temperature-dependent resistor.
• How does the resistance of a thermistor change with temperature?

  In hot conditions, the resistance decreases; in cold conditions, it increases.
• What are some applications of thermistors?

  They are used in temperature sensors, fridge temperature sensors, and thermostats.
• How do LDRs and thermistors function in sensing circuits?

  • Sensing circuits adjust power to components based on conditions.
  • LDRs decrease resistance in bright light, increasing power to connected components.
  • Thermistors decrease resistance in hot conditions, affecting power distribution.
• What happens to the potential difference across a fixed resistor and fan in a sensing circuit as the room gets hotter?

  The potential difference across the fixed resistor and fan increases.
• What happens to a bulb connected across an LDR as the room gets darker?

  The bulb gets brighter as the room gets darker.
• What are some everyday uses for LDRs and thermistors?

  • LDR: Automatic night lights
  • Thermistor: Fridge temperature sensors