1. Charge Conservation 1 TOC Origins of Charge Examples

2. Charge Conservation 2 TOC All ordinary matter consists of … ProtonsMass = 1.67x10 -27 kgCharge = +e NeutronsMass = 1.67x10 -27 kgCharge = 0 ElectronsMass = 9.11x10 -31 kgCharge = -e All ordinary matter must therefore have a total charge which is an integer multiple of e. Charge is designated by either Q or q.

3. Charge Conservation 3 TOC Example 1 Dr. Mike puts electrons on a neutral balloon by rubbing it in his hair. The balloon gains -6.3 μC of charge. How many excess electrons did the balloon receive from Dr. Mike? Answer The number is given by N electrons in the equation from the previous slide.

4. Charge Conservation 4 TOC Example 2 Dr. Mike puts electrons on a neutral balloon by rubbing it in his hair. The balloon gains -6.30 μC of charge. By how much did Dr. Mike’s weight change? Answer In Example 1, we calculated that the balloon received 3.93 x 10 13 electrons. The weight of these additional electrons is then found as follows.

5. Charge Conservation 5 TOC Example 3 Dr. Mike puts electrons on a neutral balloon by rubbing it in his hair. His hair loses 3.5 x 10 16 electrons. How much charge does Dr. Mike have when he is finished? Answer The charge is given by Q in the equation from the previous slide.

6. Charge Conservation 6 TOC Conservation The amount of charge in the universe never changes. Example Dr. Mike puts electrons on a balloon by rubbing it in his hair. The balloon gains -6.3 μC of charge. How much charge does Dr. Mike’s hair have after he has done this? Answer The electrons moved from Dr. Mike to the balloon. Thus, the charge that move to the balloon was taken away from Dr. Mike and he has +6.3 μC of charge more than he had when he began. The total charge in the universe is still the same as it was when he began.

7. Charge Conservation 7 TOC You can easily determine the number of electron and protons in a mole of some element. Example 4 How much negative electron charge is in 3 moles of oxygen? Answer There are Avogadro’s number of oxygen atoms in one mole. Using the periodic table (look it up on the web or in your chemistry textbook), we see that there are 8 electrons in on oxygen atom. And there is –e charge in each electron. So we have… Note: There are just as many protons. So 3 moles of oxygen is actually neutral.