4/18/11 1 Physics 1224/18/11 2 Physics 1224/18/11 3 Physics 1224/18/11 4 Physics 122 1.1 1.2 1.3 1.4 1.5 1.6 a 5% 3% 11% 36% 1% 13% b 85% 1% 72% 32% 4% 74% c 4% 84% 7% 21% 91% 8% d 2% 8% 4% 1% 3% 1% e 0% 0% 0% 0% 1% 1% ab 1% 0% 1% 7% 0% 0% bc 0% 1% 0% 0% 0% 0% bd 1% 1% 2% 1% 0% 0% cd 0% 1% 1% 0% 0% 0% bcd 1% 0% 1% 0% 0% 0%4/18/11 5 Physics 1224/18/11 6 Physics 1224/18/11 7 Physics 122 I would say that the biggest instance where I have tried to memorize scenarios would be in our study of electrical force and electrical fields. When give two charges, A&B, we have been asked to describe what happens to the magnitude of the force and field when we change each charge. Originally, I told myself that force is dependent on the size of the individual charges while field is not, but after examining the equation I now see that when it comes to fields, it depends on which charge I change. For force, we can easily follow Coulomb’s law (F = kqQ/r2) and see that as either one of our charges changes, the magnitude of the force changes. However, when looking at fields, it is insufficient to say, “the field does not depend on the individual changes.” For fields, we used E = F/q meaning that one of the charges (the test charge) does not affect the field. Plugging Coulomb’s law into the numerator shows us that the field does depend on the size of the charge generating the field, but not on the size of the charge we use to measure the field. SO if we have A and B, and are examining the field that A feels, then doubling the charge of A has no effect on the strength of the field, because we are examining the field generated by B. If we double B, though, then the strength of the field will double no matter what size charge is at A. Memorizing the effects of changing the system is insufficient – we can use the equation to see that the field is independent of the test charge, and then must determine which is the test charge and which charge generates the
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