P4 - Electric Circuits

• Material becomes negatively charged by

  Gaining electrons
• Material becomes positively charged by

  Losing electrons
• Two objects carrying the same type of charge

  Repel each other
• Electric field

  Region of space around a charged object in which another charged object will experience an electrostatic force
• As you get further from the charged object

  The strength of the electric field decreases
• Electric current

  Rate of flow of charge
• Units of charge, current, and time

  • Coulomb (C)
  • Ampere (A)
  • Second (s)
• There must be a source of potential difference (p.d.) in a closed circuit so that electrical charge can flow
• Factors current depends on and their units

  • Potential difference (p.d.) - unit: volt (V)
  • Resistance - unit: ohm (Ω)
• If resistance is increased but p.d. stays the same

  Current decreases
• Ohmic conductor

  A conductor where current is directly proportional to the voltage so resistance is constant (at constant temperature)
• As the temperature of a filament lamp increases

  Resistance increases
• As the temperature of a thermistor increases

  Resistance decreases
• As the light intensity on a light-dependent resistor increases

  Resistance decreases
• Series circuit

  • Same current through each component
  • Total voltage of power supply is shared between components
  • Total resistance of all components is the sum of the resistance of each component
• Parallel circuit

  • P.d. across each branch is the same
  • Total current through circuit is the sum of the currents in each branch
  • Total resistance of all resistors is less than the resistance of the smallest individual resistor
• What is the same at all points when charge flows in a closed loop?

  Current