26 1 Model Use the charge model Solve a In the process of charging by rubbing electrons are removed from one material and transferred to the other because they are relatively free to move Protons on the other hand are tightly bound in nuclei So electrons have been removed from the glass rod to make it positively charged b Because each electron has a charge of the number of electrons removed is 1 60 10 C 19 9 8 0 10 C 1 60 10 C 19 5 0 10 10 26 2 Model Use the charge model Solve a In the process of charging by rubbing electrons are removed from one material and transferred into the other because they are relatively free to move Protons on the other hand are tightly bound in the nuclei So electrons have been added to the plastic rod to make it negatively charged b Because each electron has a charge of the number of electrons added is 1 60 10 C 19 9 12 10 C 19 1 60 10 C 7 5 10 10 26 3 Model Use the charge model and the model of a conductor as material through which electrons move Solve a The charge of a plastic rod decreases from 15 nC to 10 nC That is 5 nC charge has been removed from the plastic Because it is the negatively charged electrons that are transferred 5 nC has been added to the metal sphere b Because each electron has a charge of electrons transferred from the plastic rod to the metal sphere is and a charge of 5 nC was transferred the number of 19 C 1 60 10 9 5 10 C 19 1 60 10 C 3 1 10 10 26 4 Model Use the charge model and the model of a conductor as a material through which electrons move Solve a The charge of the glass rod decreases from 12 nC to 8 0 nC Because it is the electrons that are transferred 4 0 nC of electrons has been added to the glass rod Thus electrons are removed from the metal sphere and added to the glass rod b Because each electron has a charge of electrons transferred from the metal sphere to the glass rod is and a charge of 4 0 nC was transferred number of 19 C 1 60 10 9 4 0 10 C 1 60 10 C 19 2 5 10 10 26 5 Model Use the charge model Solve Each oxygen molecule has 16 protons 8 per atom and there are of oxygen Because one proton has a charge of is 1 60 10 C 19 6 02 10 oxygen molecules in 1 0 mole the amount of positive charge in 1 0 mole of oxygen 23 6 022 10 23 16 1 6 10 19 C 1 54 10 C 6 26 6 Model Use the charge model the Solve Since 1000 mL 1 cm mL density 1 g 3 cm 1 0 L L 3 of water is 1 g cm3 the mass of 1 L of water is 1 0 kg Each water molecule H20 has 10 protons 8 in the oxygen atom and one per hydrogen atom and thus 10 electrons The number of moles is 100 mole There are 6 02 10 23 3 1 0 10 g 10 g mole water molecules in 1 0 mole of water Because one electron has a charge magnitude of negative charge in 100 mole of water is 1 60 10 19 C the amount of 100 6 022 10 23 10 1 6 10 19 C 9 6 10 C 7 26 7 Model Use the charge model and the model of a conductor as a material through which electrons move Visualize The charge carriers in a metal electroscope are the negative electrons As the positive rod is brought near electrons are attracted toward it and move to the top of the electroscope The electroscope leaves now have a net positive charge due to the missing electrons and thus repel each other At this point the electroscope as a whole is still neutral no net charge but has been polarized On contact some of the electrons move to the positive rod to neutralize some but not necessarily all of the rod s positive charge After contact the electroscope does have a net positive charge When the rod is removed the net positive charge on the electroscope quickly spreads to cover the entire electroscope The net positive charge on the leaves causes them to continue to repel 26 8 Model Use the charge model Solve a No we cannot conclude that the wall is charged Attractive electric forces occur between i two opposite charges or ii a charge and a neutral object that is polarized by the charge Rubbing the balloon does charge the balloon Since the balloon is rubber its charge is negative As the balloon is brought near the wall the wall becomes polarized The positive side of the wall is closer to the balloon than the negative side so there is a net attractive electric force between the wall and the balloon This causes the balloon to stick to the wall with a normal force balancing the attractive electric force and an upward frictional force balancing the very small gravitational force on the balloon b 26 9 Model Use the charge model and the model of a conductor as a material through which electrons move Solve The first step shows two neutral metal spheres touching each other In the second step the negative rod repels the negative charges which will retreat as far as possible from the top of the left sphere Note that the two spheres are touching and the net charge on these two spheres is still zero While the rod is there on top of the left sphere the right sphere is moved away from the left sphere Because the right sphere has an excess negative charge by the same amount as the left sphere has an excess positive charge the separated right sphere is negatively charged as shown in the third step As the two spheres are moved apart further and the negatively charged rod is moved away from the spheres the charges on the two spheres redistribute uniformly over the entire sphere surface Thus we have oppositely charged the two spheres 26 10 Model Use the charge model and the model of a conductor as a material through which electrons move Solve Charging two neutral spheres with opposite but equal charges can be done through the following four steps i Touch the two neutral metal spheres together ii Bring a charged rod say positive close but not touching to one of the spheres say the left sphere Note that the two spheres are still touching and the net charge on them is zero The right sphere has an excess positive charge of exactly the same amount as the left sphere s negative charge iii Separate the spheres while the charged rod remains close to the left sphere The charge separation remains on the spheres iv Take the charged …
View Full Document
Unlocking...