course Phy 122 Åq¤•éw€ùùóËf´Ñ£Ë¯Å¥›võ¾ç¶assignment #002
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13:34:36 In your own words explain how the introductory experience with scotch tape illustrates the existence of two types of charge.
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RESPONSE --> It illustrates this by the repulsion and attraction of the two pieces of tape. confidence assessment: 2
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13:36:05 In your own words explain how the introductory experience with scotch tape supports the idea that the force between two charged particles acts along a straight line through those particles, either attracting the forces along this line or repelling along this line.
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RESPONSE --> This idea is supported by the fact that the pieces are drawn towards or away from each other on the same plane. confidence assessment: 2
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13:37:39 In your own words explain why this experience doesn't really prove anything about actual point charges, since neither piece of tape is confined to a point.
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RESPONSE --> It doesn't prove anything because the points are changing as the two charges are brought together or pulled apart. There is no staionary point. confidence assessment: 2
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13:49:39 If one piece of tape is centered at point A and the other at point B, then let AB_v stand for the vector whose initial point is A and whose terminal point is B, and let AB_u stand for a vector of magnitude 1 whose direction is the same as that of AB_u. Similarlylet BA_v and BA_u stand for analogous vectors from B to A. Vectors of length 1 are called unit vectors. If the pieces attract, then in the direction of which of the two unit vectors is the tape at point A pushed or pulled? If the pieces repel, then in the direction of which of the two unit vectors is the tape at B pushed or pulled? Explain.
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RESPONSE --> If the pieces attract then piece A will move in the direction of AB-v. If the charges repel the tape at point B will be pushed in the direction AB-v This is because the point A tape will be drawn toward the pont B tape and will move in that direction. The tape at point B will also move in this same direction if it is being repelled from tape A. confidence assessment: 2
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13:53:49 Using the notation of the preceding question, which you should have noted on paper (keep brief running notes as you do qa's and queries so you can answer 'followup questions' like this), how does the magnitude of the vector AB_v depend on the magnitude of BA_v, and how does the magnitude of each vector compare with the distance between A and B?
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RESPONSE --> The magnatude of both AB_v and BA_v are the same. They are just in different directions. The magnitude of the vector will depend on the distance between the points. confidence assessment: 2
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13:56:35 magnitude decreases the force increases in the same proportinality. The two pieces of tape are not point charges, so this is not strictly so in this case, as some parts of the tape are closer than to the other tape than other parts.
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RESPONSE --> O.K. confidence assessment: 2
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14:02:23 Query introductory set #1, 1-5 Explain how we calculate the magnitude and direction of the electrostatic force on a given charge at a given point of the x-y plane point due to a given point charge at the origin.
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RESPONSE --> To calculate the magnitude you must first calculate the distance between the two points. using Pythagorean's therom, Then use coulomb's law to obtian the magnitude. confidence assessment: 2
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14:06:49 ** The magnitude of the force on a test charge Q is F = k q1 * Q / r^2, where q1 is the charge at the origin. The force is one of repulsion if q1 and Q are of like sign, attraction if the signs are unlike. The force is therefore directly away from the origin (if q1 and Q are of like sign) or directly toward the origin (if q1 and Q are of unlike sign). To find the direction of this displacement vector we find arctan(y / x), adding 180 deg if x is negative. If the q1 and Q are like charges then this is the direction of the field. If q1 and Q are unlike then the direction of the field is opposite this direction. The angle of the field would therefore be 180 degrees greater or less than this angle.**
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RESPONSE --> OK self critique assessment: 2
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14:13:23 Explain how we calculate the magnitude and direction of the electric field at a given point of the x-y plane point due to a given point charge at the origin.
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RESPONSE --> We first need the x,y coordinates of the point. Then we will use each x,y coordinte to determine the distance of the pont charge from the origin, by using Pythagoreans's Therom. C^2=A^2+B^2 After finding the distance of the point charge from the origin we can then use coulomb's law to determine the magnitude of the field. confidence assessment: 2
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14:22:02 ** The magnitude of the force on a test charge Q is F = k q1 * Q / r^2, where q1 is the charge at the origin. The electric field is therefore F / Q = k q1 / r^2. The direction is the direction of the force experienced by a positive test charge. The electric field is therefore directly away from the origin (if q1 is positive) or directly toward the origin (if q1 is negative). The direction of the electric field is in the direction of the displacement vector from the origin to the point if q1 is positive, and opposite to this direction if q1 is negative. To find the direction of this displacement vector we find arctan(y / x), adding 180 deg if x is negative. If q1 is positive then this is the direction of the field. If q1 is negative then the direction of the field is opposite this direction, 180 degrees more or less than the calculated angle. **
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RESPONSE --> OK self critique assessment: 2
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