Friday, February 19, 2010
Effects Of An Electric Current
-Electrical energy can be transformed into other forms of energy to produce many effects.
Heating Effect Of A Current
-When a current passes through a wire, the wire heats up. This is caused by the conversion of electrical energy into heat energy. The heat produced depends on the resistance of the wire.
Heating appliances usually have coils of wires or heating elements inside.
These heating elements are made of high resistance materials such as nichrome.
The heating elements heat up when current is passed through them.
Magnectic effect of a current
If an iron rod is placed inside the coil of wire, it makes the magnetic field a few hundred times stronger. When the current is switched off, the iron loses its magnetism. This set-up is known as electromagnet, and it is used in many applications. It gives a magnetic field that can be switched on and off when desired.
Applications of the magnetic effect of current
-A giant elecromagnet can be used to separate iron from non-iron scrap, to be recycled. The electromagnet can also be used to lift heavy iron and steel objects.
-A telephone makes use of a small electromagnet in the speakers and microphones.
-Electric motors, run by electromagnets, are used in many household appliances such as fans, and to run electric trains. A coil of wire wound a round a soft iron core is placed in between the poles of a permanent magnet. When a current passes through the coil, it becomes an electromagnet. It then spins under the influence of the magnetic field of the permant magnet. This set-up is called motor.
Chemical Effect of a current
-Liquids that allows electricity to pass through them are called electrolytes.
-The chemical decomopsition of an electrolyte by an electric current is called electrolysis.
-The two wires or plates through which current enters and leaves the electrolyte are called electrodes.
Application of the chemical effect of current
-Electrolysis is used in a process called electroplating. In this process, the flow of current causes a thin layer of metal to be deposited on the object to be electroplated.
-Electrolysis is also used in industries to extract metals such as aluminium from their compouds. To extract a metal, a solid compound of the metal is heated until it melts. An electric current is then passed through this molten compound. For example, aluminium is obtained from molten aluminium oxide.
9:55 PM
Tuesday, February 16, 2010
RESISTANCE
-The components in a circuit resists the flow of electrons thus, the current does not flow easily in a circuit.
-The resistive force is called the resistance (R) of an object.
-The resistance of a component is the ration of the potential difference across it to the current flowing through it.
-S.I unit for resistance is ohm (Ω)
Varying Resistance in an electric circuit
Varying Resistance in an electric circuitFixed Resistors
-Specially made resistors of a specific value.
Variable resistor (Rheostats)
-Used to vary the current flowing in a circuit, by the varying resistance.
-Used to vary the current flowing in a circuit, by the varying resistance.
4:35 PM
Saturday, February 13, 2010
POTENTIAL DIFFERENCE 
-Electric current can only flow when there is a potential difference (V) or (p.d.) to push the charges around a circuit.
-Charges will always flow from higher to lower potential.
-The potential difference across any two points is the amount of energy needed to move one unit charge of electricity from one point to another.
-S.I. unit is Volt (V)
Measuring potential difference
-Voltmeter is used to measure potential difference.
-Voltmeter must be connected parallel to the component.
11:00 AM
Saturday, February 6, 2010
Electricity
Electric Current
-Flow of electricity is due to the movements of electric charges.
Circuit symbols:
Series and Parallel circuits
-Two main types of circuits: Series and Parallel.
Measuring Current
- A form of energy.
Electric Current-Flow of electricity is due to the movements of electric charges.
-Two types of charges: Positive (+) and Negative (-)
-When electric charges move, an electric current is formed (I).
-Is the rate of flow of electrical charges.
-The path that current flows is known as a circuit.
-Measured by the amount of charges moving past any point in the circuit per second.
-S.I unit is amphere (A)
Electric Circuits
Circuit symbols:Series and Parallel circuits-Two main types of circuits: Series and Parallel.
Measuring Current-Ammeter is used to measure current.
-Ammeter must be connected in series with the circuit. 
4:39 PM
Wednesday, February 3, 2010
COLOURS
Primary colours are basic colours that cannot be obtained by mixing other colours of light.
Primary Colours of light are: Red, Blue and Green.
Secondary colours are formed by mixing primary colours.
Secondary colours are: Cyan, Yellow and Magenta.
We are able to see the colour of an object as it reflects that colour into our eyes.
For example when white light falls on a green object, the object absorbs all the other colours and reflects only green light.
When we shine red light on a green object, the object will appear black as the green object can only reflect green light therefore, when red light is shone onto a green object, it is not refected and so the object would appear black.
This tells us that in order to see the colour of the object, the light shone must have the same colour as the object, the colour is then reflected and seen by our eyes.
Primary colours are basic colours that cannot be obtained by mixing other colours of light.
Primary Colours of light are: Red, Blue and Green.
Secondary colours are formed by mixing primary colours.
Secondary colours are: Cyan, Yellow and Magenta.
We are able to see the colour of an object as it reflects that colour into our eyes.
For example when white light falls on a green object, the object absorbs all the other colours and reflects only green light.
When we shine red light on a green object, the object will appear black as the green object can only reflect green light therefore, when red light is shone onto a green object, it is not refected and so the object would appear black.
This tells us that in order to see the colour of the object, the light shone must have the same colour as the object, the colour is then reflected and seen by our eyes.
8:15 PM
Monday, February 1, 2010
Dispersion Of White Light
-Sunlight appears to be white but it is actually composed of different colours.
1. When a beam of white light passes through a prism, it is split into different colours.
2. This is because the different colour of white light bend towards the normal through different angles when entering the prism and when leaving the prism too.
3. A spectrum of colours is produced, which is made up of seven colours: Red, Orange, Yellow, Green, Blue, Indigo, Violet. This splitting of white light is called dispersion.
5:30 PM
