think about using furry elephant trial version., very good from what i saw.
Which of the following machines do / don't need electricity
current as a flow of charge;
An electric current is the flow of electrons around a conductive path (a circuit made of conducting wires).
I like to imagine the current to be like a river carrying water down from a place of higher ground down to the sea.
The difference in the height of the river is like in mechanics the potential of the electricity, more often called the Voltage, this is what gives the electricity its speed / power.
The Current in electricity is the number of electrons that pass a point per second. It is like a measure of flow water, in little water molecules per second.
It should be seen that electricity and water are similiar in the way they act (in some ways), water and electricity are dangerous if a great deal of it flows quickly.
q's 1-5 pg 326
conductors and insulators
So there will only be current flowing through a conductor, so we need to be able to define / classify a material as a conductor or an insulator.
OP49 test electrical conduction in a variety of materials, and classify each material as a conductor or insulator
OC44 investigate the ability of ionic and covalent substances to conduct electricity
An early guess about the nature of electricity suggested that some sort of positive particles flowed from + to -. This is referred to as "conventional current"
Ben Franklin: The Plus and Minus.
From The First American: The Life and Times of Benjamin Franklin,
by H.W. Brands,
here is a description of Franklin's ongoing correspondence begun in 1747 with Peter Collinson in London. Collinson was an agent of the Library Society of Philadelphia, and a scholar with scientific interests similar to Franklin's:
"In one of his first letters, Franklin supplied a novel terminology that became standard in analyzing electrical phenomena. Describing a particular apparatus, consisting of bodies labeled A and B, he wrote: 'We say B (and other bodies alike circumscribed) are electrised positively; A negatively. Or rather B is electrised plus and A minus ….' At a time when other electricians spoke of two different kinds of electricity — vitreous and resinous — Franklin unified the field by positing a single sort and explaining the opposite properties in terms of a surfeit or a deficit (that is, positive condition or negative) of this single electricity, with uncharged objects being in balance."
The discovery of the electron led to the realization that electricity is probably a flow of electrons from - to +. This has led to a confusing situation with text books using one or the other or both explanations.
I prefer the electron model. The electron model is more in keeping with the actual action of the particles within materials, the electrons are almost 1/2000th the mass of a proton, this allows them to move quicker than protons. So most electricity flow is actually electrons doing the moving. Thus the electron model says that electricity goes from the 'high ground' of the negative side of the battery to the lower potential of the positive side of the battery / power source.
OP51 demonstrate simple series and parallel circuits containing a switch and two bulbs
simple circuits—series and parallel; function of a switch
relationship between voltage, current and resistance;
OP50 set up a simple electric circuit, use appropriate instruments to measure current, potential difference (voltage) and resistance, and establish the relationship between them
OP52 perform simple calculations based on the relationship between current, potential difference (voltage), and resistance
heating, chemical and magnetic effects of an electric current;
OP53 describe the heating effect, the chemical effect, and the magnetic effect of an electric current, and identify everyday applications of these, including the action of a fuse
direct and alternating current;
OP54 distinguish between direct and alternating current;
recall that the voltage of the mains supply is 230 volts a.c.
There are 2 types of electric current
Alternating and Direct
A.C. Alternating Current
Is the electricity that comes from the sockets in our homes
It is more efficient way to transport large amounts of electricity.
The electricity changes direction every 1/100th of a second.
High power devices at home use A.C.
A.C. can be converted into D.C easily
DC - Direct Current
Batteries provide Direct Current,
the electrons go from the negative end to the positive end
Very simple to build circuits
Most devices in our homes can use D.C.
difficult to convert into A.C.
As useful and as easy to understand as DC is, it is not the only “kind” of electricity in use. Certain sources of electricity (most notably, rotary electro-mechanical generators) naturally produce voltages alternating in polarity, reversing positive and negative over time. Either as a voltage switching polarity or as a current switching direction back and forth, this “kind” of electricity is known as Alternating Current (AC)
Electricity from the ESB, is alternating.
This means that the direction that the electrons flow changes all the time.
In fact it changes 50 times every second.
We say that electricity supply has a frequency of 50Hz
The reason for Alternating current is due to the cyclical nature of electricity generation.
Simple alternating electric circuits mr Fendt
the voltage of the mains supply in Ireland (& most of europe) is 230 volts a.c. Most power tools used in construction are only rated at 120V which is the same as most of the Americas
OP55 recall that the unit of electrical energy used by electricity supply companies is the kilowatt-hour, and calculate the cost of using common electrical appliances, based on their power rating
units used in calculating electricity bills
For some really dull but energy effiecent work lets go to
Use this to calculate the trends in the school bills
The BBC shows us how to calculate the power used
Energy (kWh) = Power (kW) x Time (hours)
Pick your favourite appliance at home (write it down)
What is its power rating (wattage) ?
How long do you use it for every week ?
Cost of Energy (€) = Energy (number of kWh) x unit price (€)
Energy is usually measured in Joules, however a Joule is a small amount of energy and might not be as easy to calculate as the kiloWatthour. In order to calculate the number of kWh, we need to determine the power of the appliance in kiloWatts. If the device is given its power rating in just watts then you must divide this value by 1,000 to find the number of kiloWatts. The time is to measured by the number of hours the device is in use. In reality we have meters in our houses (some of these meters are actually outside the house in a plastic doored cabinet at the side of your house.
calculations of kWh
power rating of electric appliances;
Homework find the power rating of 5 appliances in your home.
at home investigate / calculate / the power rating of different appliances
make a table
How long are each of these appliances on for every day ?
Work out the kWhs for each appliance for a week / month!
Now, work out the cost per day.
power ratings for computers & the like
wiring a plug;
OP56 describe how to wire a plug correctly, and explain the safety role of a fuse or circuit breaker in domestic electrical circuits
Wiring a plug
Prepare the plug:
- Remove the cover and loosen the screws of the cord grip
- Loosen the screws from the brass terminals
Prepare the flex:
- Measure the flex against the plug and strip the outer covering back as far as the cord grip, taking care not to cut through the coloured insulation on the wire strands
- If the coloured cables have to be trimmed, ensure that they are long enough to reach the terminals without straining. Allow for a little slack on the green/yellow earth wire
- Strip about 10 mm (1/2 inch) of the coloured insulation from each core
Fixing the flex to the plug:
- BROWN to the LIVE (L) terminal
- BLUE to the NEUTRAL (N) terminal
- GREEN/YELLOW to the EARTH (E) terminal
- (What about appliances with 2-core flexes?)
- Pass the flex under the loosened cord grip
- Twist the exposed wire strands of each core between your finger and thumb so that there are no loose strands
- If the plug has clamp terminals, wrap each core around the appropriate terminal; place the washer on top of the twisted wire and tighten the screw nuts firmly. Make sure that the coloured insulation is not pinched under the terminal clamp.
- If the plug has pillar terminals, double the twisted bare wire back on itself for about 5 mm, and insert it fully into the hole in the appropriate terminal. Tighten the terminal screw firmly on the wire.
- Tighten the cord grip screws, making sure that the cord grip is clamped on the full outer covering of the cable and not on the inner cores.
- Replace the cartridge fuse in 13 Amp plugs with an appropriate sized fuse:
- Blue 3-Amp fuse for lights and small appliances
- Brown 13-Amp fuse for larger appliances and heaters
- Replace the cartridge fuse in 13 Amp plugs with an appropriate sized fuse:
- Replace the cover
mains supply; fuses and circuit breakers and their role in safety;
action of a fuse
A fuse is a safety device that is rated for a certain current (amps). If the current is greater than the rating it causes the thin wire inside the fuse to melt. This melted fuse breaks the circuit thus prevents electricity from passing.
- Remember the colour code:
Miniature Circuit Breakers,
are safety devices that 'trip out' when a current is too large. They can be used multiple times as they are just automatic switches.
The use of fuses is now restricted to fuses found inside plugs. The main circuit board is no longer kept safe by these devices.
A Miniature Circuit Breaker and a Residual Current Breaker
Show how a fuse works.
Electrical circuit. Steel Wool. Variable resistance. Bulb.
Make up a circuit, include an ammeter and a bulb to show there is electricity passing around the circuit.
Break the circuit by turning off the PSU.
Add some steel wool to the circuit.
Turn back on the PSU, observe the bulb the ammeter and the steel wool.
Take note of the condition of each of these factors over the next few minutes.
Be sure that you can turn off the power without reaching over the circuit