PHYS-102 SPRING-08 QUIZ-II Time Limit: 50 min.
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Name______________________ Recitation Sec.#_______
Notes:1. For problems 2 and 3, your solutions must have adequate details to get full credit.
F = qE
1 2
2
kQ Q
Fr
=
1/4πε0 =
9 2 2
9 10k x Nm C !
=
U = kQ1Q2/r ; V = kQ/r ; 1/C = 1/C1+ 1/C2+1/C3+…. C= Q/V
C = C1 + C2 +C3+…. U = QV/2 ;
Δ
Wfield = -
Δ
U ; Ex = - dV/dx
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NOTE: For Prob .1, below, please circle the answer of your choice for each part.
1a.( 3pts.) Suppose at one instant the electrons and the
nucleus of a helium atom occupy the positions as shown.
The electric potential energy of this charge configuratio n
is:
[a] – 3.5kQ2/r [b] – 4kQ2/r [c] zero [d] + 4kQ2/r
1b. ( 3pts.) Two capacitors are connected in series as shown with
C1=2C2. If U1 and U2 are, respectively the potential energy stored in
C1 and C2., which of the following statements is true?
[a] U1 = 2U2 [b] 2U1 = U2 [c] U1 = U2 [c] 4U1 = U2
1c. ( 3pts.) When the potential difference bet ween the plates of a capacitor is doubled, the
potential energy stored in the capacitor is:
[a] doubled [b] halved [c] unchanged [d] quadrupled
1d. ( 3pts.)Consider two conducting metallic spheres S1 and S2. The radius of S1 is half that of
S2. Each sphere is given some excess charge such that both spheres have the same potential at
their surfaces. This implies that:
[a] S1 and S2 have equal charges.
[b] S2 has more charge on it than S1 .
[c] S1 has more charge on it than S2
r r
-Q +2Q -Q
C1C2
!=25 V
