Electricity

identify common materials that are electrical conductors

copper, aluminium, silver and gold

identify common materials that are electrical insulators

rubber, plastic, glass, ceramic, and dry wood

how can insulating materials be charged by friction?

Two insulators are rubbed together

friction causes electrons to move from one to the other

Material that loses electrons becomes positively charged

material that gains electrons becomes negatively charged

magnitude of charge on each material is equal- they lose/gain the same number of electrons

explain the uses of electrostatic charges in a photocopier

drum is given positive charge

light is shone onto drum

negatively charged toner is applied

toner pattern is transferred to paper

paper is heated to fuse toner

explain the uses of electrostatic charges in inkjet printers

ink is broken into droplets

droplets are given charge

deflector plates create an electric field

field exerts a force on the droplets

charge controls where they land

What are the potential dangers of electricity when fuelling aircraft and tankers?

Fuel flows through pipes- causes friction

builds up static charge

spark can occur- fuel vapour is flammable

Spark → ignition → fire or explosion risk

how does the use of insulation/double insulation protect the device/user

Insulation

—> rubber or plastic coating around wires prevents contact with live wires, stopping shocks.

Double Insulation

—> doesn’t need earth wire because outer casing is second layer of insulation, eliminating shock risk even if internal wires wear out. 

how does the use of earthing protect the device/user

Metal-case is connected to earth wire, if live wire touches case, earth wire has low resistance path to earth and blows fuse

how does the use of fuses and circuit breakers protect the device/user

Contains thin wire that melts if current exceeds its rating, breaking the circuit

how does the use of circuit breakers protects the device/user

automatic switch that opens circuit when current is too high

why does a current in a resistor result in increase in temperature

Flowing electrons collide with metal ions, transferring kinetic energy into heat, causing resistor to warm

what is the difference between alternating current (a.c.) and direct current (d.c.)

Flow: AC flows back and forth; DC flows one way.

Voltage: AC voltage varies; DC voltage is steady.

how does the current in a series circuit depend on the applied voltage

the current is directly proportional to the applied voltage and inversely proportional to total resistance, which increases with number and type of components

What is current?

Measured in amps (A)- the rate of flow of charge

What is potential difference?

Measured in volts (V)- work done per unit charge in moving between two points in a circuit

What is resistance?

Measured in ohms- the opposition to the flow of current

Resistor at a constant temperature

Current and voltage with a filament lamp

Current and voltage in a diode

Explain the resistor at a constant temperature graph

In an ohmic conductor the current is directly proportional to the voltage

Explain the current and voltage with a filament lamp graph

temperature in the filament increases as the current does, which means electrons and ions vibrate and collide more, increasing resistance.

Explain the current and voltage in a diode graph

A diode only allows current to flow in one direction

in reverse direction, diode has very high resistance, and therefore no current flows

what is electric current in solid metallic conductors?

a flow of negatively charged electrons

why is current conserved at a junction in a circuit

electrons can't be created or destroyed, so total current entering a junction must equal total flow leaving it

switch

cell

battery

diode

resistor

variable resistor

lamp

fuse

voltmeter

ammeter

thermistor

LDR- Light dependent resistor

LED- Light emitting diode

function of live wire

carries the high alternating voltage (240V) from the mains supply to the appliance, delivering the electrical power

what affects resistance in circuits?

longer wire

thinner wire

higher temperature

explain the practical for investigating how insulating materials can be charged by friction

Rub the insulating rod (plastic/acetate) with a dry cloth

Bring the rod near small pieces of paper

Observe what happens (attraction or repulsion)

what are the control variables for investigating friction on insulating materials?

Same material

same number of rubs

dry conditions (humidity)

what are the strengths of series circuits?

• Simple to construct and understand

• components controlled by a single switch

• Less wiring needed

what are the weaknesses of series circuits?

• If one component breaks, the whole circuit stops working

• Adding more components increases resistance, reducing current throughout

what are the strengths of parallel circuits?

• If one component breaks, the others continue working

• Each component gets full supply voltage

what are the weaknesses of parallel circuits?

more complex to construct

requires more wiring