You are blowing bubbles, using a bubble wand that has a circular loop at one end

Question

You are blowing bubbles, using a bubble wand that has a circular loop at one end with a radius of 1.40 cm. You hold the wand so that the area vector of the loop points in the same direction as a uniform electric field of 23.2 N/C. (a) What is the electric flux through the flat soap film that spans the loop before you begin to blow? (b) What would the electric flux be if the area vector had pointed in the opposite direction? (c) Now you blow in the same direction as the electric field, and the film bulges out to form the greater part of a spherical surface of radius 3.34 cm. What is the flux through the film now? (d) You blow some more, and the film detaches to form a complete spherical bubble of radius 3.46 cm, which floats off the wand. What is the net flux through the bubble?

Explanation / Answer

For a, you first need to find the area of the circle, which is pi(r)^2. Be sure that you convert the cm to meters, also. So, it is pi(0.014m)^2 = 6.1575x10^-4 m^2. Multiply this by 23.3 N/C, and you will get 0.01428 N/C*m^2.

For b, it is just the negative of part a, so -0.01428 N/C*m^2.

I can't figure out part c,

Part d is 0, because there is no net flux through the bubble.

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