Mains and Current electricity

• Conductor is a material that allows charge to flow through it easily. e.g metals.
• Insulators are materials that do not allow charge to flow through them easily. e.g plastic, wood, rubber.
• • An ammeter is the size of current flowing in a circuit .
  • An ammeter is always connected in series with the part of the circuit being investigated.
• • Electromagnetic force is the amount of energy given charges by a cell or battery.
  • It is measured in volts (v).
• There are two types of circuits:

  • Series circuit- It is a single lamp circuit. In a series circuit, there is only one path for current to flow.
  • Parallel circuit- A parallel circuit has more than one path. The current through each component may not be the same.
• Difference beteewn parallel and series circuits:

  • In series circuit, one switch can turn all copmponents on and off, if one component breaks, it creates a gap in the circuit. No current wil flow, hence all components will go off,the voltage supplied by the cell is shared between all component, hence if more bulbs are added, they become dimmer.
• In parallel circuits, switches can be placed in different parts of the circuit to turn off or on individual components, if one bulb breaks, the other bulbs can still light, each branch of the circuit recieves the same voltage, therefore if more bulbs are added they will all stay bright.
• • An incomplete circuit has a gap therefore, no current flows through it.
  • A complete circuit does not have a gap therefore, current flows through it.
• Resistance is the opposition to the flow of charge.
• Resistors are devices or components in a circuit that offer resistance to flow of charge.
• Types of resistance:

  1. Fixed resistor-It is a resistor whose resistance is constant. They are included in circuits to control the size of current and voltage. This makes them be used to protect components.
  2. Variable resistor- This is a resistor whose resistances can be increased or decreased. If the resistance of a variable resistor is increased a smaller current flows in the circuit however, if the resistance is decreased a larger current flows.
• 3. Thermistor- It is a resistor whose resistance changes with temperature. At room temperature they have a small number of free elctrons, hence a large resistor. When warmed the number of free electrons increases and resistance decreases.

  4. Light Dependent Resistor (L.D.R)- It is a resistor whose resistance changes when light shines on it. L.D.R are used in light sensitive circuits in devices like photographic equipment, automatic lighting controls and bulgar alarms.
• 5. Diode- It is a special resistor that allows current to flow through it in only one direction. In one direction, current flows quite easily through it, it has low resistance. If current flows in the opposite direction, it has a very high resistance and no current can flow.

  6. Light emitting diodes (LED)- These are diodes that glow when a current is flowing through it.
• Why are metals good conductors of electricity

  In metal wires, charge is carried by electrons so, electrons will flow easily in metals.
• Mains electricity is electricity we use at home and is supplied by power generating stations, E.g Tv, electric cookers use mains electricity supply.
• The ring mains circuit consists of three wires:

  1. Live wire (red or brown)
  2. Neutral wire (blue)
  3. Earth wire (green and yellow stripes)
• Live wire provides the path along which electric current from the power station travels to the appliances.
• Neutral wire completes the circuit by carrying current from the appliance back to the source.
• Earth wire protects the user if the appliance develops a fault.
• A Fuse is a cylindrical catridge containing a thin piece of wire made from a metal having a low melting point.
• Electrical power is the rate at which electrical energy is connected to other forms.
• Double insulation is when the appliance has metallic parts covered by an insulator so that the user cannot touch them.