Electricity Chapter Notes | Year 4 Science IGCSE (Cambridge) - Class 4 PDF Download

Which Materials Conduct Electricity?

• A conductor is a material that allows electricity to pass through it.
• Examples include metals like copper, iron, and steel, which facilitate the flow of electric current.

• An insulator is a material that does not allow electricity to pass through it.
• Examples include plastic and wood, which block the flow of electric current.

• When testing materials for conductivity, safety precautions are critical.
• Use wire strippers to remove plastic insulation from wires, stripping away from the body to avoid injury.
• Avoid touching bare wires when the circuit is complete to prevent electric shock, handling only plastic-covered wires.

Does Water Conduct Electricity?

• Water from natural sources (e.g., rivers, taps) is not pure and contains dissolved salts.

• Distilled water is pure, created by boiling water and condensing the steam back into liquid, removing all salts.
• It contains no dissolved salts, unlike tap or river water.
• Human bodies are approximately 65% water, with dissolved salts, making them capable of conducting electricity.

• Pure (distilled) water does not conduct electricity due to the absence of ions.
• Water with dissolved salts (e.g., saltwater) conducts electricity because salts dissociate into ions, which carry electric current.

Using Conductors and Insulators in Electrical Appliances

• Electrical appliances use conductive materials, such as metals (copper, iron, steel), for parts that need to carry electricity.
• Example: The pins in a plug are made of metal to allow electricity to flow from the wall socket to the appliance (e.g., kettle, television).

• Insulating materials, such as plastic, are used for parts of appliances that users touch to prevent electric shock.
• Example: The cover of a plug is made of plastic, a good insulator, to ensure safe handling.

• Mains electricity powers household appliances (e.g., microwaves, kettles, power drills) and has a higher voltage than battery cells.
• Voltage varies by country: 110 V in some, over 200 V in others, compared to 1.5 V or 3 V for safe classroom circuits.
• Pylons carry high-voltage electricity (thousands of volts) via cables from power stations to homes, factories, and offices.

• Mains electricity passing through the body can cause severe burns, heart failure, or death due to electric shock.

• Damaged wiring, where plastic insulation wears off, exposing conductive copper wires.
• Placing wires under carpets, where foot traffic can wear off insulation, leading to shocks or fires.
• Improper plug removal (e.g., yanking the cord) can expose wires, increasing shock risk.
• Overloading sockets by plugging in too many devices, which can cause shocks or fires.
  

• Turn off the power switch before removing a plug, and grip the plastic plug body to avoid contact with bare wires.
• Avoid handling electrical appliances with wet or sweaty hands, as water enhances conductivity, increasing shock risk.

Switches

• A switch is a component in an electrical circuit that controls the flow of electric current by opening or closing the circuit.
• Closing the switch completes the circuit, allowing current to flow and the device (e.g., a lamp) to operate.
• Opening the switch breaks the circuit, stopping the current and turning off the device.
• This is analogous to turning a tap on or off to control water flow.

• Switches allow users to control electrical devices (e.g., turning a lamp on or off) without physically breaking wires, unlike circuits without switches.

• A basic switch can be made using conductive materials (e.g., metal paper clip, drawing pins) to connect or disconnect the circuit.
• The base of the switch is made from an insulating material (e.g., wood) to prevent unwanted current flow.
• Conductive components complete the circuit when in contact and break it when separated.

• When stripping plastic insulation from wires, use wire strippers or a knife carefully, cutting away from the body to avoid injury.
• Use a non-conductive tool (e.g., wooden or plastic stick) to manipulate the switch to avoid electric shock.

• An electrical device (e.g., a lamp) will not work if there is a break in the circuit, as the current cannot flow.
• Proper connections are essential; loose or incorrect connections can prevent the circuit from functioning.

Changing the Number of Components in a Circuit

• A cell is a single unit that stores electrical energy, typically providing 1.5 volts (V) of electricity.
• A battery consists of two or more cells connected together to provide a higher voltage.
• Example: A car battery delivers 12 V, while two 1.5 V cells combined (as used in experiments) provide 3 V.
• When a cell or battery is part of a circuit, the stored energy drives the electric current through the circuit.

• Changing the number or type of components (e.g., cells or lamps) in a circuit affects the brightness of lamps.

• Adding more cells (increasing voltage) provides more energy, causing lamps to shine more brightly.

• Adding more lamps divides the available energy among them, causing each lamp to shine more dimly.

• Safety is critical when working with electrical circuits to prevent shocks or injuries.
• Use wire strippers or a knife carefully to remove plastic insulation from wires, cutting away from the body.
• Handle components with non-conductive tools (e.g., a wooden or plastic stick) to avoid contact with live wires.