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course Phy 202
3/30 10 am
I left off the questions you said we'd leave for Monday:
3.23.11
`q001. How much energy does it take to move a 2 microCoulomb charge from x = 30 cm to x = 10 cm, given a field of 8 * 10^5 Newtons / Coulomb directed in the positive x direction?
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8x10^5 N/C * 2x 10^-6 C=1.6 N
`dW=+1.6 N * (10 cm-30 cm)=-32 N/cm=-.32 J
.32 J/2x10^-6 C=1.6 x 10^5 J/C
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`q002. How much force is experienced by a 1 microCoulomb charge at the point (30 cm, 40 cm) by a 3 microCoulomb charge at the origin?
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.108 N
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What is the direction of this force?
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Away from origin, extending from the last point.
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How much work would it take to move the 1 microCoulomb charge one centimeter closer to the origin?
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.108 N * 1 cm=.00108 J
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How many Joules does it take per Coulomb of moving charge to move that one centimeter?
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`dPE/ q= .00108 J/ 1x10^-6 C=1080 J/C (volt)
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What is the electric field at the point (30 cm, 40 cm) due to a 3 microCoulomb charge at the origin?
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@& The electric field at a point is equal to the force experienced by a charge at the point, divided by the charge.
The force is .108 N and the charge experiencing the force at the point (30 cm, 40 cm) is 2 microCoulombs.*@
`q003. A volt is a Joule of potential energy per Coulomb.
How much does chemical potential energy stored in a 1.5 volt battery change, per minute, as it drives a .20 amp current?
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.20 amps=.2 C/s
1.5 volt=1.5 J/C
.2 C/s*1.5 J/C=.3J/s
.3J/s * 60 s=18 J
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By how much does the electrostatic potential energy of a capacitor change in 200 milliseconds, if the capacitor is at 6 volts and drives a current of 50 milliamps?
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6 volts=6 J/C 50mA=.050 C/s
6 J/C * .050 C/s=.3 J/s
In 200 mseconds, the energy loss is .3 J/s *.2 s=.06 J
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How much energy does it take to light your lightbulb at 1.5 volts for 10 seconds?
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I’m afraid I’m over simplifying this:
1.5 volts= 1.5 J/C over 10 seconds
1.5 J/C * 10 seconds==I know that’s not right because I don’t end with a unit of energy.
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@& You should have observed the current through the bulb. Probably around 100 milliamps. That allows you to figure out how many J / sec, etc..*@
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Self-critique (if necessary):
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Self-critique rating:
@& Good. See my notes on a couple of questions and let me know if the answers aren't fairly obvious, with a little thought.
Also, I have put notes on your test in the gradebook.*@