Electrical Circuits

Simple Electrical Circuits
Electricity will only flow in a complete circuit.


The bulb is connected in a circuit to a battery using two wires.


Electricity will not flow if the circuit is not complete .

Look carefully at the drawing and decide why the circuit is not complete.

If you were going to describe an electric circuit to someone, it is likely that you would want to draw it.

If you connected a bulb, battery and a switch, the circuit drawing might look like this:







It takes time to draw such a circuit and because people might draw batteries and bulbs etc. in different ways it could be very confusing.

It is easier if people use the same symbols in a circuit diagram.

Some Electrical Symbols


a connecting wire


a bulb

a switch

a battery


a motor

a buzzer

A Simple Circuit and its Symbols
Now if you were to draw the previous electrical circuit using the symbols it would look like this:




The original circuit using, battery, switch and bulb looked like this:

Batteries and Bulbs
You need the following:
Wire



Bulb

Bulb holder

Battery




Examine the battery. Write down as many things about it that you can.

Draw and label a picture of the battery in your notebook.



1. Try to get the bulb to light using the wire, bulb and battery.
2. Try to get the bulb to light using the wire, bulb, bulbholder and battery.
The bulb will only light if it is connected to the battery in an Electric Circuit.
A Current flows round the circuit.

To get your bulb to light, you should have set your materials like this:





Now unscrew the bulb from the bulb holder and look at it closely. The thin wire is called the filament.





What happens to the filament when you put the bulb back into the electrical circuit?





Write about your experiments and draw circuit diagrams to show how you set up the circuits.

1. Make an electrical circuit.
You will need: 4.5v batteryBulb and bulb holder4 paper clipsCovered copper wire
Scrape the covering off the ends of a 30cm length of wire. Twist one end round a paper clip. Do the same with another 30 cm length of wire and another clip.Fasten the clips to the terminals of the battery. Press the free ends of the wire to the bulb.
See what happens.
You have made a simple electric circuit.
Now screw the free ends of the wires to the terminals on the bulb holder and screw in the bulb.
Cut through one of the wires.
See what happens.
Scrape the covering off the ends of the wire you have just cut.
Twist each of these round a paper clip and press the two clips together.
See what happens.
What happens when you release your clips?
See if you can write about what happens and why.
2. Make an electrical conductor tester.
You will need: 4.5v batteryBulb and bulb holder4 paper clipsCovered copper wire
First make an electric circuit similar to the one you have just made.
Leave a small gap between the two paper clips which make up the switch.
Place an iron nail across the gap so that it touches both of the clips.See what happens.
Does the nail conduct electricity?
Test other materials to see if they are conductors or non-conductors of electricity e.g. pin, pencil, hair clip, scissors, straw, silver paper, coin, rubber band, various metals, paper clip.

Materials which can carry electric current are known as CONDUCTORS OF ELECTRICITY

Materials which cannot carry electric current are known as NON-CONDUCTORS OF ELECTRICITYOR INSULATORS


Metals are conductors.

Most non-metals are non-conductors.
Graphite and some liquids and solutions are non-metals but can conduct electricity.

Static Electricity

Static Electricity
Rubbing the surface of a material with another material can make it have an electric charge.
If you rub two balloons with a piece of woollen cloth, they will repel each other.



You can tear some tissue paper into small pieces.



Now rub a glass rod with a piece of silk. Now bring the rod near to the tissue paper and notice what happens.



Rubbing the glass rod with the silk makes it lose electrons, so it becomes positively charged. The silk gains electrons and becomes negatively charged. The neutral tissue paper is attracted by the rod.

Static Electricity
You can do some simple experiments with static electricity. They work best on cold, dry days.
Rub a plastic comb hard with a woollen cloth.


Bring the comb near to some small pieces of paper and find out what happens.



Rub a sheet of paper hard with a brush. Bring a corner of it near to a table tennis ball. Notice what happens.



Place a sheet of paper against a smooth painted wall. Hold it in place and rub it firmly with a brush. What happens when you take your hand away?


Comb your hair with a plastic comb. Bring it near to some small pieces of paper. What happens?



Rub a balloon hard on the front of your sweater. Now put it near a smooth, painted wall. What happens?

Lightning
Lightning is an example of static electricity in nature.



Clouds can become heavily charged with electricity. Lightning, which is a heavily charged electrical spark then passes between the clouds and the earth.

Lightning Safety
Although lightning is common, few people are hurt by it.

Lightning follows simple paths to the ground. To stay safe, keep away from tall trees in a thunderstorm, and do not stand in fields or on the top of a hill.



Lightning conductors are used on tall buildings where they allow electricity to discharge harmlessly, leaving the building undamaged.
Rub a balloon hard again, but this time bring it near to someone's hair (preferably long and without gel). What happens?

Electricity

Electricity
Electricity is very important in our lives.
We would find it very hard to do without it.


There are so many things in our homes that are powered by electricity that we have begun to depend on them.

We have toasters.


We have CD players.


In our homes we have TV


We have refrigerators.


We use computers


The list is almost endless.

Mains Electricity
Most of the large appliances in our home are powered by Mains Electricity.


An electric cooker is connected to the mains electricity supply.


Lots of the appliances are fitted with plugs that can be inserted into a socket.


A microwave cooker is fitted with a plug that connects it to the mains electricity supply.




A percolator is fitted with a plug that connects it to the mains electricity supply.



Electricity can be dangerous!
Never play with plugs or sockets, or anything that uses electricity.


Electricity can kill!

Never play near pylons or overhead cables.

Never play near train lines.

Battery Power
Many small electrical appliances use batteries.

Portable radios use batteries.


Mobile phones rely on batteries.

Some cameras and video cameras use batteries.


Flashlights use batteries.


Some toys use batteries.

Magnets

The first magnets were known as magnetite or lodestone.




It is said that a Cretan shepherd called Magnes first noticed lodestone when the iron-tipped end of his crook was pulled down when he passed a certain rock.




The ancient Greek scientist, Archimedes is believed to have used lodestone to pull nails from enemy ships, which then sank.



Sailors used lodestone to help them navigate. They had found that when a piece of magnetite was suspended from a thread it came to rest in a North-South direction.

Magnetic Materials
Objects such as pins and nails are magnetic.

Screwdriver and hatchet blades can be magnetic.

Objects such as wood, glass and plastic are non-magnetic.

Types of Magnets
There are different types of magnets. Some of these are:
Horsehoe Magnets
Bar Magnets
Ball-ended Magnets
Circular Magnets

Poles of Magnets
The ends of magnets are called poles. Most of the magnetism is concentrated in the poles.
If you hang a bar magnet from a thread it will come to rest in a direction facing North-South

Magnets behave differently depending on which poles you bring together
Bring a North-seeking pole near to a South-seeking pole. The magnets are attracted.

Bring a South-seeking pole near to a South-seeking pole. The magnets repel each other.

The Law of the magnet is:
Like poles repel.

Unlike poles attract.


Magnetic Fields
There is an area round the magnet in which magnetic materials are attracted by the magnet.
This is called the Magnetic Field.

How can you show these lines of force?

Place a bar magnet under a piece of paper. Sprinkle coarse iron filings over the paper and gently tap until they form a pattern.
This will show the lines of force of the magnetic field.


Place two bar magnets under a piece of paper. Place the North-seeking poles opposite each other.Sprinkle coarse iron filings over the paper and gently tap until they form a pattern.
This shows the lines of force of the magnetic field.
In the middle there is a neutral zone where there is no magnetic field.

Place two bar magnets under a piece of paper. Place a North seeking poles near to a South-seeking pole. Sprinkle coarse iron filings over the paper and gently tap until they form a pattern.
This will show the lines of force of the magnetic field.

What are Magnets?
Magnets are usually made of iron or steel.


Powerful magnets can be made of special alloys of aluminium, cobalt, copper, nickel and iron.
Materials can be permanent magnets.


Materials can be induced magnets.

All materials are made of very small particles called molecules. The molecules of iron and steel are magnetic. The Molecular Theory of Magnetism suggests that in a magnet all the molecules are lined up with their own North-seeking and South-seeking poles as in the diagram. This means all the souths are pointing one way and all the norths pointing in the other direction.

In an unmagnetised piece of iron or steel the molecules are arranged at random with the poles pointing in lots of different directions.

You can show this with a large test tube of iron filings. The tube must be almost full and corked securely. the iron filings can be seen to lie in almost every direction. If you bring this tube towards a compass needle, it has almost no effect on the needle. Stroking the test tube, in a horizontal position with the North-seeking pole of a magnet causes the iron filings to line up as in the diagram.
Iron filings lined up after stroking with magnet.

Making Magnets
There is a picture of a smith hammering steel to make a magnet, in a book called De Magnete written by Queen Elizabeth I's physician Dr William Gilbert.
Heating and hammering with a steel bar in a North-South direction can make a magnet.






This causes the molecules to line up in the North-South orientation.





Stroking a piece of unmagnetised iron or steel with a known magnet can make it into a magnet.

This causes the molecules to line up in the North-South orientation.





Placing a magnet alongside a non-magnetised steel knitting needle for some time will magnetise it.

This causes the molecules to line up in the North-South orientation.





Placing an object such as a non-magnetised steel knitting needle in a north-south position will allow it to become a magnet through the influence of the earth's magnetic field.

This causes the molecules to line up in the North-South orientation.

Demagnetizing
A magnet can be destroyed by hammering



This causes the molecules to become arranged at random with the poles pointing in lots of different directions.







Heating a piece of magnetized iron or steel strongly in a flame will demagnetize it.



This causes the molecules to become arranged at random with the poles pointing in lots of different directions.

Magnetism and Electricity
In 1819, Hans Christian Oersted, a Danish scientist was experimenting with electricity.


Oersted noticed that a compass needle moved when a current flowed through a wire nearby.

If you wrap a 10 cm length of bell wire round a pencil in a single layer coil and connect the ends to a 3v battery, you will make a solenoid. Bring a compass needle towards this and watch what happens.

You should find that the compass needle changes direction to line up with the centre of the coil because the coil behaves like a magnet.


If you reverse the battery terminal wires, then the compass needle should reverse. It will still be lined up with the pencil, but in the opposite direction.

Electromagnets
You can make an electromagnet from an iron nail and a length of bell wire.



Wrap the insulated wire round the nail. About 20 turns should make a good magnet.





Connect the wires to a battery. You can put a switch in the circuit.



Close the switch to complete the circuit and see if you can use the magnet to pick up some drawing pins.
Find what happens when you switch off.





The nail should pick up drawing pins when you switch on.



The pins should fall off when you switch off.

Using Electromagnets
An electromagnet can be used for moving scrap steel from one place to another. In a scrapyard, a crane has a large iron disc that is not a permanent magnet.

The crane operator lowers the electromagnet into a pile of scrap steel and then switches on the electricity. This causes the steel disc to become a powerful magnet. Scrap steel is attracted to the disc.


When the operator switches off the electricity, the scrap steel falls off the disc.

In this way, large amounts of scrap steel can be moved easily from one place to another.