The figure shows four Gaussian surfaces surrounding a distribution of charges. W

Question

The figure shows four Gaussian surfaces surrounding a distribution of charges. Which Gaussian surfaces have no electric flux through them? a b b and c b and d c Answer: E When the current through a resistor is increased by a factor of 2 (necessarily changing the voltage), the power dissipated by it decreases by a factor of 2. increases by a factor of 2. decreases by a factor of 4. increases by a factor of 4. remain unchanged. Answer: D A rectangular coil, with comers labeled ABCD, of length L and width w is placed in a magnetic field B as shown in the figure. If there is a current I flowing through this coil, what is the direction of the force acting on section AB of this coil? perpendicular to and into the page perpendicular to and out of the page in the direction of the magnetic field in the opposite direction of the magnetic field in the direction of the current Answer: A

Explanation / Answer

1) electric flux = Qin/epsilon

for the surface C, Qin = q-q = 0. so, electric flux is zero.

2) P = I^2*R

when current becomes twice power dissipated becomes 4 times.

3) F = I*(L cross B)

so F is perpendicular to L and B. so it points in to the page.

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