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An experiment studying the strength of the repulsive electric force between two identically charged

Redraw the above example assuming all charges are positive. Also, use the same y-distances of 5. Calculate a the angle that each of F13 and F23 makes with the positive x-axis. If you feel you are not ready for this problem now, do it after you go through "Test Yourself 1", completely. Chapter 18 Test Yourself 1: There are 3 types of electrons: Bound electrons are the inner shells electrons that are under strong Coulomb forces from nucleus and difficult to detach.

Valence electrons are the outer shells electrons and participate in chemical reactions. They are easier to remove from the atoms. Free electrons do not belong to any particular atom.

They flow in between atoms under the repulsive forces from the electron clouds of different atoms and the smaller attraction forces from the nuclei of the closest atoms. The electric conductivity of a substance depends on its number or abundance of free electrons. A metal contains a large number of free electrons. A nonmetal contains few free electron. Semiconductors are alloys of metals and nonmetals.

The have controlled conduction properties depending on their metal percentages. If electricity accumulation of negative or positive charges can not flow easily, it causes localized charges and forms static electricity. This happens when a bunch of electrons, for example, is given to an insulator.

Because of lack of free electrons in the insulator, the transferred electrons stay locally and do not distribute in the insulator quickly.

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They form static electricity. If a conductor mounted on an insulatoris given a number of excess electrons, the electrons distribute themselves in that conductor; however, the insulator mounting stops the electrons from flowing into the mounting and it becomes a boarder for the free electrons.

In the conductor part, since the excess free electrons repel each other, they locate themselves as far from each other as possible. For a sphere, the farthest possible distance is a uniform distribution of charges over its external surface. For other shape objects, it depends on the geometry. The following figure shows a metal sphere as well as an oval-shaped metal object, both on insulator mountings. The sphere becomes positive and the oval negative.

Note the higher concentration of electrons at the farthest possible distance, the sharper edges. Charging of an Object: An object may be given electric charges in two ways: When a charged object is brought into contact with an uncharged electrically neutral object, part of its charges flow onto the uncharged object and make it partially charged. The transfer proportion depends on the shapes of the two objects.

For example, if the two objects are two identical metal spheres with insulator mountings, they share the charge equally. For asymmetric and unequal objects, the reasoning is more complicated and involved. The following figure shows the simple case of two identical metal spheres on insulator mountings a before contact, b during contact, and c after separation.

Charging by induction means charging without contact. The Earth may be considered as being electrically neutral. Adding a certain number of positive or negative charges to the Earth does not affect its neutrality. Earth is so huge that the charges on the objects do not count at all compared to the charges that the Earth contains.

That is why Earth is electrically neutral for our experiments. We can easily transfer some charges to it or take from it and it will not be affected. If an electrically charged sphere on an insulator mounting is connected with a conductor a metal wire to the ground, it gets discharged either by transferring some electrons to the Earth or pulling some from it.

Section 1 Electric Charge: Review

The following figure shows how a positively charged sphere and a negatively charged one become discharged by being connected to the Earth. Charging an Object Positively by Induction: If a plastic rod is rubbed against wool, it becomes negatively charged. If the rod is brought near a neutral metal sphere that is on an insulator mounting, it repels the free electrons of the sphere to the far end of it.

At the same time, the rod attracts the positive charges of the sphere to the very near end of it. If the far end is connected to the Earth by a wire, the electrons flow to the ground while the positive charges are held captive by the rod. When the connection with the ground is cut off, the rod may be taken away leaving the sphere with positive charges. The process is shown below: Charging an Object Negatively by Induction: To be explained by students with appropriate figures.

Anywhere there is an electric charge, q1there exists the property of attraction or repulsion on other charges placed around it. This effect of attraction or repulsion is called the electric field of q1. Again, k is called the Coulomb's constant. The way the electric field strength E of a point charge q weakens with r is like the way light intensity weakens as we move away from a light bulb. Suppose you have built an empty sphere out of glass that has a surface area of 1 ft2 and has a tiny light bulb at its center.

Also suppose that you have made another glass sphere whose radius is twice the first one and is around the first sphere. It is easy to show that when you double the radius of a sphere, its area quadruples 4 ft2. You have already figured it out that the same amount of light energy that distributes over the inner sphere must an experiment studying the strength of the repulsive electric force between two identically charged the outer sphere and distribute over it.

Since the same energy is given to an area 4 times greater; therefore, the intensity becomes 4 times weaker. What would happen to the light intensity brightness if you made glass spheres with radii 3x, 4x, 5x, 6x, and so forth? One unit of positive charge is called a test charge. The farther the test charge, the weaker the force of repulsion. For a negative charge -qa similar situation is shown below. When a test charge is placed at different points around a negative charge -q, it will be attracted by a force.

The farther the test charge, the weaker the force of attraction. Note that the direction of the attraction force is always along the line connecting -q and the test charge and acts inward as shown below: Field Strength of a -q charge. Such two equal and opposite charges form the so-called an "electric dipole. The meaning of each field line is as follows: The space around these two charges contains infinite number of points. Since each field acts along the line that connects the charge to a given point, vector addition must be employed in order to find the resultant field.

The following example clarifies the need for vector addition: In the figure shown, find the resultant field at each point where there is a charge.

For example, when finding the field at where q1 is, suppose q1 is nonexistent and find the resultant field by q2 and q3 at that point. A Good Link to Try: Make sure to turn the "Potential Lines" off. Only have the " Electric Field Lines" selection turned on.

PPLATO / FLAP (Flexible Learning Approach To Physics)

An electric field is called uniform if its strength does not change with distance. The electric field of a point charge is not uniform, because it strongly weakens when distance from the charge increases. Is it possible to create an electric field that does not change with distance? The answer is "yes". If two parallel metallic plates are separated by a distance and connected to a battery, one plate accumulates some negative charges while the other plate accumulates equal amount of positive charges.

The electric field in between the plates and specially away from the edges will essentially be uniform and the electric field lines become parallel.

Such a device forms the so-called parallel-plate capacitor. The following figure shows the difference between the non-uniform field of a point charge and the uniform field of a parallel-plate capacitor. In the figure shown, find a the force on the oil drop of mass 2.

PHYS 3.3: Electric charge, field and potential

The charge on each after being brought into contact is a 4. The charge on each after being brought into contact is a Two identical metal spheres A and B are on their insulator mountings, both initially neutral. A is on the left and B on the right. They are first brought into contact.


Draw a figure for it. The field strength is The force on the charges are: Draw a figure for the problem. Find d the magnitude and direction of the force of Q1 on Q2 that you may name F Find e the magnitude and direction of the force of Q3 on Q2 that you may name F Finally, find f the magnitude and direction of the resultant force on Q2 that you may name R.