physics

• Static electricity

  Electricity that is not moving, where charges move to stick from one object to the next
• Charge

  A property of matter that experiences a force when next to other charges or in an electric field
• Coulomb

  The unit of measurement for charge
• Electric field

  The region around a charge where other charges experience a force
• Electric field lines

  • Direction shows the force on a positive charge
  • Spacing shows the field strength
• Charging an insulator

  1. Rub with another insulator

  2. One object loses electrons, the other gains electrons
• Charging by induction

  Inducing a charge on a metal object by bringing a charged object close and connecting to ground
• Current electricity

  Electricity where charges are moving in a circuit to deliver energy from a source to a device
• Voltage

  The amount of energy per charge, measured in volts
• Potential difference

  The voltage across a component like a resistor
• Electromotive force (EMF)


  The voltage of a power source like a battery
• Current

  The rate of flow of charges, measured in amperes
• Current conventionally flows from positive to negative
• Resistance tries to slow down the flow of charges through a component
• Friction between charges and a component releases electrical energy as heat
• Circuit symbols

  • Battery
  • Switch
  • Light bulb
• The purpose of a circuit is to deliver energy from a power source to a device that needs it
• Current is defined as the rate of flow of charges, which is the number of charges that go through the circuit per second
• Current


  How fast the charges go around the circuit
• Current is often from positive to negative, which is called conventional current, but the charges that actually move are electrons from negative to positive
• Resistance


  A property that resists the flow of charges
• The higher the resistance of a material, the lower the current
• Voltmeter


  Instrument used to measure voltage, connected in parallel
• Ammeter


  Instrument used to measure current, connected in series
• Ohm's Law


  V = IR, R = V/I, I = V/R
• For Ohm's Law to work, the resistance of a resistor must be constant
• Resistance increases with temperature because atoms vibrate faster and collide more with electrons
• Increasing resistance


  Decreases current
• Current is constant throughout the circuit, it does not change within the circuit
• Resistance does not affect voltage, only current
• Resistance


  Directly proportional to length, inversely proportional to cross-sectional area
• Power

  Energy over time, calculated as V x I
• Energy


  Power x Time
• Kilowatt-hour


  Measure of energy consumed by 1000 watts of power in one hour
• Thermistors have resistance that decreases as temperature increases, opposite to fixed resistors</b>
• LDRs have resistance that decreases as light intensity increases
• Variable resistor


  A resistor that can change resistance that affects current
• Thermistor


  A type of variable resistor that changes based on temperature - the hotter it is, the lower the resistance, and the lower the temperature, the higher the resistance
• Thermistors are made of non-metallic conductors, and when heated, they gain more free moving electrons so they become better conductors
• As temperature increases


  Resistance of a thermistor decreases