Electrons Can Be Transferred from One Object to Another by Friction

Electric Fields

Field Theory: A force is a push or a pull. A field is a region where an object may experience a force. The field has a source, which is an object which exerts the force. A force can be gravitational, electric, or magnetic in nature. Fields of force have direction and magnitude (an amount of strength) and so we can call them vector fields and represent them mathematically using vectors.

Forces can be represented using field lines. The field lines indicate the direction of the force. The force is more intense where the field lines are the most dense. Field lines may not cross. Fields of force can interact with each other.

Electric forces can be attractive or repulsive. Like charges repel each other with an electric force of repulsion. Unlike charges similarly attract each other with a force. The attractive force between unlike charges acts just like the gravitational force between two masses. Two objects with unlike charge attract each other. Two objects with like charges repel each other.

Electrons orbit the nucleus of an atom. Some The amount of charge on an object is the number electrons are loosely held and can be transferred of electrons in excess or deficit. It is a comparison from one object to another. of the numbers of electrons and protons. Electrons can be transferred from one object to another by friction.

The electric force exerted by one object on another depends on the charges on the two objects and how far apart they are.

Compare the concepts of gravitational force and electric force using the Venn diagram below. Turn text to visual to explore and develop your understanding and interpretation of the reading..

The electric potential at a certain location in a field is V and is the amount of electric energy per unit charge q.

∆E q

Pulling your wool sweater off makes your hair stick up because of the static charge that develops. Friction between the wool and your hair causes electrons to move to the material with the higher attraction for them. Why does pulling off your sweater cause a spark to jump from the sweater back to the person? The following selection from your text explains how lightning is produced.

Think back to the last time you saw a sky like this. Can you remember what the weather was like that day?

At first, this may seem like a ridiculous question, but it is not coincidence that most thunderstorms occur late in the afternoon or evening of a very hot, humid summer day. The reason for this is that it takes the intense summer sun to make the air hot and rich in water vapour. Warm air floats up in cooler surrounding air—like a cork in water. As it rises, the water vapour starts to condense and forms a cloud. The condensation releases energy, which causes the air parcel to get even warmer and rise even higher.

Sometimes the top of a thundercloud can reach 12–20 km above the ground! As a column of warm water vapour rushes up, it comes in contact with a column of condensed water droplets that are descending. Since the water droplets more readily hold on to their electrons than the rising water vapour does, electrons are transferred from the rising water vapour to the descending water droplets. The result is that the bottom of the cloud has an excess of electrons, so it is negatively charged. The top of the cloud has lost electrons, so it is positively charged.

Recall from previous courses that objects with opposite charges attract each other, while objects that have the same type of charge repel one another A lightning strike transferred about 15 C of charge from a cloud to a building. The voltage between the cloud and the building was 1.50x108 V.

a) Calculate the energy delivered in the b) A typical home in Alberta uses 3.0 x 109 J lightning strike of electrical energy every month. Comparethis amount to the amount of energy in the lightning strike.

Read about fields and field lines in your text unit C 1.1 p.312-327.