1) 1 microfarad capacitor is connected to a power supply until it acquires a pot

Question

1) 1 microfarad capacitor is connected to a power supply until it acquires a potential difference of 700 V across its plates, then the power supply is removed. If the capacitor is then connected to a 200 kiloohm resistor, what is the voltage across the capacitor 7.0 milliseconds later?

2) two charges separated by 1 meter, exert an electric force of 2N on each other. If the charges are pushed together so that they are now only 1/7th of a meter apart, the electric force wil now be?

3) when I make microwave popcorn, my oven projects an average power of 1.0KW of of microwaves into a 0.25m by 0.35m area for 2 minutes and 20 seconds. Calculate the peak electric field strength of these waves.

4)a very myopic person has a prescription of -5.00D to allow her to see objects at distance. What is her far point when not wearing glasses?

5) calculate the optical power of the eye when viewing an object 2.00m away. Assume that the eye behaves as a single thin lens that the distance from the lens to the retina is 2.0cm.

Explanation / Answer

a) voltage will fall exponentially

as v(t) = V* exp(-t/(r*c))

where r and c are resistance and capacitance.

so puuting the values we get

v(at 7m sec) = 675.62 volts

b) force is inversely proportional to the square of the distance

so we get,

F1R1^2 = F2R2^2

we get force = 98 N

e)

v= -2 cm

u= 200 cm

we got f = v*u/(u-v)= - 1.98 cm

power = 1/1.98 = 0.505 diopters

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