Electricity

• Current is the flow of electrons (charge) around a circuit, measured in amperes (A) by ammeters (connected in circuit)
• Electrons move from negative to positive.
• Charge flow (Q) is the product of current (I) and time (t).
• Potential Difference (P.D) is the difference in the amount of energy that charge carriers have between two points in a circuit, measured in Volts (V) by a voltmeter (connected in parallel)
• Resistance is the measure of how a device or material reduces current through it, and resistance RESISTS current.
• Resistance is measured in Ohms (Ω).
• Factors that affect resistance include the length/thickness/type/temperature of wire.
• Resistance (R) is equal to Potential Difference (P.D) divided by current (I).
• Ohmic conductor obeys ohm’s law.
• Non-ohmic conductor does not obey ohm’s law.
• UK plugs have 3 pins and they link appliances to the national grid’s 230V mains electricity.
• Fuse is a thin piece of wire which will melt if too much current passes through it and it keeps us safe and prevents electrical fires.
• • Electric current (conventional) flows from positive to negative
• Label:

  A) Resistor

  B) Filament Lamp

  C) Diode

  
• Label:

  A) earth

  B) Neutral

  C) Live

  D) Fuse

  
• In a series circuit: Current is the same everywhere, Voltage is shared. Vtotal=V1+V2+V3 and Resistance is shared. Rtotal=R1+R2+R3
• In a parallel circuit: Current is split. Itotal=I1+I2+I3, Voltage is the same for each component and Total Resistance is less than the resistance of smallest resistor.
• P.D = Energy transferred (E) / Charge (Q)
• What system is used to distribute electricity in the UK?

  The National Grid
• Why must the National Grid accurately distribute electricity?


  Because the demand for electricity changes throughout the day
• Why is the potential difference (P.D.) high in the National Grid?


  To prevent unwanted energy transfer
• What causes static electricity?


  Friction created when certain insulating materials are rubbed together
• What happens to electrons when certain insulating materials are rubbed together?


  Negatively charged electrons transfer from one material to the other
• What is the result of the transfer of electrons between two materials?


  One material becomes positively charged and the other negatively charged
• Which particles can move to create electric charge?


  Only electrons can move
• What happens as electric charge builds up on an object?


  The potential difference between the object and the earth increases
• What can happen if the potential difference is large enough?


  Electrons can jump between the object and the earth, causing a spark
• What is typically the size of the spark caused by static electricity?


  Normally a small spark
• How does lightning occur in relation to static electricity?


  It occurs when a large potential difference allows electrons to jump through the air
• What is created around any electrically charged object?


  An electric field
• In which direction do electric field lines go?


  From positive to negative
• How does the strength of an electric field change with distance?


  The closer you are to the charged object, the stronger the field is
• What happens when a charged object is placed in the electric field of another object?


  It feels a force that causes either attraction or repulsion
• Why do charged objects experience attraction or repulsion in an electric field?


  Because the fields interact with each other
• Fill in the blanks:

  A) Station

  B) Step-up

  C) Step-down

  D) Reduces

  
• Fill in the blanks:

  A) Away

  B) Towards