Section 2: Electricity Flashcards
Understand the uses of insulation, double insulation, earthing, in a range of domestic appliances
Insulation is covering a live wire with a material that won’t conduct the electricity.
Double insulation is a precaution that makes sure the live wire cannot touch the casing usually by putting extra insulation round that wire. An earth wire is touching the case so that if a current is in the case, it will be directed through the earth wire, this will then take the current to the earth. Additionally the surge of electricity in the wire may break the fuse.
Fuses are sections of wire in the circuit that melt if too high a current goes through them. They come with different maximum currents.
Circuit breakers have an electromagnet that is activated if the current goes above a certain limit. the electromagnet pulls an iron switch towards it, this opens the switch and breaks the circuit.
Understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature
When electric current flows through a resistor some of the energy is transferred to heat energy. This results in the resistor heating up
Know and use the relationship: power = current × voltage P=I×V
Power = Current x Voltage
Use the relationship between energy transferred, current, voltage and time: E=I×V×t
Energy = Current x Voltage x Time
Understand the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery.
AC fluctuates between max voltage and min voltage, for example mains goes from +240V to -240V
DC Stays at maximum voltage, for example a 9V battery will stay at max voltage of 9V
Explain why a series or parallel circuit is more appropriate for particular applications
Series: A washing machine requires a series circuit so it can have 2 switches, for saftey. EG the washing machine cannot start unless the door is closed
Parallel: Lighting systems would require a parallel circuit as if 1 light breaks the others still work
Describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature
Thermistor: Low Temp = High Resistance
LDR: Low Temp= High Resistance
Know and use the relationship between voltage, current and resistance
Voltage = Current x Resistance
Know and use the relationship between charge, current and time:
Charge = Current x Time
Know that electric current in solid metallic conductors is a flow of negatively charged electrons
Electric current exists as a constant flow of negatively charged electrons
Identify common materials which are electrical conductors or insulators, including metals and plastics
Conductors: Copper, aluminum, graphite
Insulators: Plastic, Rubber
Describe experiments to investigate how insulating materials can be charged by friction
Get a polyethene rod and rip up some small pieces of paper; the rod will have no effect on the paper.
Rub the polyethenerod with a cloth, now the rod will attract the pieces of paper, this is because it now has a charge they are attracted to.
Explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons
As electrons are negatively charged, when an atom loses them the atom becomes positively charged.
If the atom gains them they become negatively charged
Explain electrostatic phenomena in terms of the movement of electrons
Electrons move from one material to another, the material with a negative charge will then look for some way to earth its charge
Explain the potential dangers of electrostatic charges, EG when fuelling aircraft and tankers
When a large electrostatic charge builds up it can create a spark. Whenrefuellingvehicles the fuel rubbing along the pipe can cause an electrostatic charge, if this sparks if couldignitethe fuel causing a fire or explosion
