What kind of charges repel each other

Both are expressed through field contours; field forces act in the direction of the contours, and the distance between the contours indicates their magnitude. The closer the contours are together, the larger the force. In an electric field the direction of the field is given by the electric charge of the charged sources. If the charge is negative, the field is directed toward the charge. All electric fields begin on a positive charge and end on a negative charge.

Suppose that you rubbed a balloon with a sample of animal fur such as a wool sweater or even your own hair. The balloon would likely become charged and its charge would exert a strange influence upon other objects in its vicinity.

If some small bits of paper were placed upon a table and the balloon were brought near and held above the paper bits, then the presence of the charged balloon might create a sufficient attraction for the paper bits to raise them off the table.

This influence - known as an electric force - occurs even when the charged balloon is held some distance away from the paper bits. The electric force is a non-contact force. Any charged object can exert this force upon other objects - both charged and uncharged objects. One goal of this unit of The Physics Classroom is to understand the nature of the electric force. In this part of Lesson 1, two simple and fundamental statements will be made and explained about the nature of the electric force.

These two fundamental principles of charge interactions will be used throughout the unit to explain the vast array of static electricity phenomena. As mentioned in the previous section of Lesson 1 , there are two types of electrically charged objects - those that contain more protons than electrons and are said to be positively charged and those that contain less protons than electrons and are said to be negatively charged.

These two types of electrical charges - positive and negative - are said to be opposite types of charge. And consistent with our fundamental principle of charge interaction, a positively charged object will attract a negatively charged object. Oppositely charged objects will exert an attractive influence upon each other. In contrast to the attractive force between two objects with opposite charges, two objects that are of like charge will repel each other.

That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart.

Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other. This electric force exerted between two oppositely charged objects or two like charged objects is a force in the same sense that friction, tension, gravity and air resistance are forces.

And being a force, the same laws and principles that describe any force describe the electrical force. According to Newton's third law, a force is simply a mutual interaction between two objects that results in an equal and opposite push or pull upon those objects. Let's apply Newton's third law to describe the interaction between Object A and Object B, both having positive charge.

Object A exerts a rightward push upon Object B. Object B exerts a leftward push upon Object A. See diagram at right. These two pushing forces have equal magnitudes and are exerted in opposite directions of each other. Each object does its own pushing upon the other.

Because of the away from nature of the mutual interaction, the force is said to be repulsive. Now let's apply the same action-reaction principle to two oppositely charged objects - Object C positive and Object D negative. Object C exerts a leftward pull upon object D. Object D exerts a rightward pull upon Object C. Again, each object does its own pulling of the other. Just as before, these two forces have equal magnitudes and are exerted in opposite directions of each other.

However in this instance, the direction of the force on Object D is towards Object C and the direction of the force on Object C is towards object D. Because of the towards each other nature of the mutual interaction, the force is described as being attractive. The interaction between two like-charged objects is repulsive.

The interaction between two oppositely charged objects is attractive. What type of interaction is observed between a charged object and a neutral object? The answer is quite surprising to many students of physics. Any charged object - whether positively charged or negatively charged - will have an attractive interaction with a neutral object. Positively charged objects and neutral objects attract each other; and negatively charged objects and neutral objects attract each other.

Thus, the comb itself never accumulates too much charge, because any charge it gains is quickly depleted by the charge moving to the outer surface of the globe. Van de Graaff generators are used to demonstrate many interesting effects caused by static electricity. By touching the globe, a person gains excess charge, so his or her hair stands on end, as shown in Figure You can also create mini lightning bolts by moving a neutral conductor toward the globe.

Another favorite is to pile up aluminum muffin tins on top of the uncharged globe, then turn on the generator. Being made of conducting material, the tins accumulate excess charge. They then repel each other and fly off the globe one by one. A quick Internet search will show many examples of what you can do with a Van de Graaff generator.

This simulation allows you to observe negative charge accumulating on a balloon as you rub it against a sweater. You can then observe how two charged balloons interact and how they cause polarization in a wall. Click the reset button, and start with two balloons. Charge a first balloon by rubbing it on the sweater, and then move it toward the second balloon. Why does the second balloon not move? This lab will demonstrate how water molecules can easily be polarized.

What do you observe? What happens when the plastic object touches the water filament? Can you explain your observations? Electrically neutral ink droplets in an ink-jet printer pass through an electron beam created by an electron gun, as shown in Figure Some electrons are captured by the ink droplet, so that it becomes charged. How many electrons are captured by the ink droplet? The number n of electrons captured by the ink droplet are.

This is almost a billion electrons! It seems like a lot, but it is quite small compared to the number of atoms in an ink droplet, which number about 10 How many protons are needed to make 1 nC of charge? Which are the two main electrical classifications of materials based on how easily charges can move through them? True or false—A polarized material must have a nonzero net electric charge. Describe the force between two positive point charges that interact.

True or false—Charging an object by polarization requires touching it with an object carrying excess charge.

As an Amazon Associate we earn from qualifying purchases. Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4. Changes were made to the original material, including updates to art, structure, and other content updates. Skip to Content Go to accessibility page. Physics My highlights. Table of contents. Chapter Review. Test Prep. By the end of this section, you will be able to do the following: Describe positive and negative electric charges Use conservation of charge to calculate quantities of charge transferred between objects Characterize materials as conductors or insulators based on their electrical properties Describe electric polarization and charging by induction.

Teacher Support The learning objectives in this section will help your students master the following standards 5 The student knows the nature of forces in the physical world. The student is expected to: C describe and calculate how the magnitude of the electrical force between two objects depends on their charges and the distance between them; and E characterize materials as conductors or insulators based on their electrical properties. In addition, the High School Physics Laboratory Manual addresses content in this section in the lab titled Electric Charge as well as the following standards: 5 The student knows the nature of forces in the physical world.

Teacher Support Prepare a demonstration of static electricity. Note that the size of the nucleus is vastly exaggerated in this drawing.

Were it drawn to scale with respect to the size of the electron orbits, the nucleus would not be visible to the naked eye in this drawing. Also, as far as science can currently detect, electrons are point particles, which means that they have no size at all! Measuring the Fundamental Electric Charge The American physicist Robert Millikan — and his student Harvey Fletcher — were the first to make a relatively accurate measurement of the fundamental unit of charge on the electron.

By knowing the mass of the oil droplets and adjusting the electric charge on the plates, the charge on the oil drops can be determined with precision. Like and Unlike Charges This activity investigates the repulsion and attraction caused by static electrical charge. Adhesive tape Nonconducting surface, such as a plastic table or chair Instructions Procedure for Part a.

Like charges attract, while unlike charges repel each other. Like charges repel, while unlike charges attract each other. Tapes having positive charge repel, while tapes having negative charge attract each other.

Tapes having negative charge repel, while tapes having positive charge attract each other. What is the missing charge? The law of conservation of charge allows us to find the final charge q red q red on the red sphere.

Which equation describes conservation of charge? If object 1 loses half of its charge, what is the final charge on object 2? Teacher Support [BL] Have students define the meaning of conductor and insulator. The slashes on the arrow mean that there is a very large gap in conducting ability between conductors, semiconductors, and insulators, but the drawing is compressed to fit on the page.

The resistivity is a measure of how hard it is to make charge move through a given material. Teacher Support Point out that the scale is not linear, which means that the conductivity of the insulators is much, much less than that of conductors.

The electrons repel each other and spread out to cover the outer surface of the sphere. The electrons cannot move, so they remain in their original positions. Teacher Support Point out that static buildup does not remain forever on an object. After the transfer, both spheres have 75 excess electrons. In the bottom row, a metal sphere with excess protons receives 25 electrons from a ball with 50 excess protons.

After the transfer, both spheres have 75 excess protons. Teacher Support Point out how the total charge at each instant is the same. Each sphere now carries an equal magnitude of excess charge. Teacher Support Discuss the analogous situation with insulating spheres. Create a Spark in a Science Fair Van de Graaff generators are devices that are used not only for serious physics research but also for demonstrating the physics of static electricity at science fairs and in classrooms.

The upper comb has no excess electrons, and the excess electrons in the rubber belt get transferred to the comb by contact. The upper comb has no excess electrons, and the excess electrons in the rubber belt get transferred to the comb by conduction. The upper comb has excess electrons, and the excess electrons in the rubber belt get transferred to the comb by conduction.

The upper comb has excess electrons, and the excess electrons in the rubber belt get transferred to the comb by contact. Balloons and Static Electricity Click to view content.

The second balloon has an equal number of positive and negative charges. The second balloon has more positive charges than negative charges. The second balloon has more negative charges than positive charges.

The second balloon is positively charged and has polarization. Polarizing Tap Water This lab will demonstrate how water molecules can easily be polarized. Plastic object of small dimensions, such as comb or plastic stirrer Source of tap water Instructions Procedure. Why does the water curve around the charged object? Charging Ink Droplets Electrically neutral ink droplets in an ink-jet printer pass through an electron beam created by an electron gun, as shown in Figure When you bring all three spheres together so that they all touch one another, what is the total charge on the three spheres?

How many types of electric charge exist? The force is attractive and acts along the line joining the two point charges. The force is attractive and acts tangential to the line joining the two point charges. The force is repulsive and acts along the line joining the two point charges. The force is repulsive and acts tangential to the line joining the two point charges.

How does a conductor differ from an insulator?