PHYS 259 Playground

 $\$  Consider four identical dipoles of the same dipole moments  of magnitude p placed in a uniform electric field of strength E (as shown in the picture).

Which dipole experiences torque of magnitude pE in +z direction?

• A

• B

• C

• D

A rod of length L carries charge Q. Which of the expressions correctly describes the equation for the y-component of the electric field due to the entire rod?

• $\left|E_y\right|=\int_{-0.25}^{0.75}\ \frac{k_e\lambda\ Ldy}{4\ \left(x^2+\frac{L^2}{4}\right)^{\frac{3}{2}}}$

• $\left|E_y\right|=\int_{-0.25}^{0.75}\ \frac{k_e\lambda xdx}{\ \left(x^2+\frac{L^2}{4}\right)^{\frac{3}{2}}}$
  

• $\left|E_y\right|=\int_{-0.25}^{0.75}\ \frac{k_e\lambda\ Ldx}{4\ \left(x^2+\frac{L^2}{4}\right)^{\frac{3}{2}}}$

• $\left|E_y\right|=\int_{-0.25}^{0.75}\ \frac{k_e\lambda\ ydx}{4\ \left(x^2+\frac{L^2}{4}\right)^{\frac{3}{2}}}$

Which Gaussian surface has the net flux of

 $-\frac{q}{\varepsilon_0}$  ?

• A
  

• B
  

• C
  

• None of them
  

Consider two rings, one with radius R carrying charge Q1 and one with radius nR, carrying charge Q2, both placed in the x-y plane and centered at the origin. The electric potential at point P is equal to zero. Which statement is correct?

• Q1/Q2 is negative and |Q1|<|Q2|

• Q1/Q2 is positive and |Q1|<|Q2|

• Q1/Q2 is negative and |Q1|>|Q2|

• Q1/Q2 is positive and |Q1|>|Q2|

Which figure correctly shows the electric potential for a conducting sphere of radius R carrying positive charge Q?

• Figure A

• Figure B

• Figure C

• Figure D