Download Test 2 Solution

Phy207 Exam II (Form1) Professor Zuo Spring Semester 2015 “On my honor, I have neither received nor given aid on this examination” Signature:______________________ Name:___________________ #1‐14 #15 Total ID number:___________________ Enter your name and Form 1 (FM1) in the scantron sheet. Attempt all problems. Multiple choice questions are worth 5pts each and the essay problem is 30 pts. There is a formula sheet attached at the end. This is a closed book exam, you must work independently! No collaboration is allowed. Prohibited items: any electronic devices including cell phones and calculators, pens, backpacks, notes, books. Anyone found cheating during the exam will automatically receive an “F” grade for the course and sent to the honor’s court. Put an X next to your discussion section:
[ ] Dr. Mezincescu 5O, 9:30 – 10:20 a.m.
[ ] Dr. Zuo 5P, 11:00 – 11:50 a.m.
[ ] Dr. Zuo 5R, 2:00 – 2:50 p.m.
(For the next two problems) A parallel plate capacitor is made of two square sheets of metals of side
length L with a separation d between each other. Half of the space is filled and the other half empty. The
filled half is filled with two dielectrics with dielectric constant k1 and k2, as shown.
1) Find the capacitance of the capacitor
A)
B)
1
C)
D)
E)
2) Find the charge on the area just above the filled space if k1=2, k2=6.
A) Q , B) Q, C) Q, D) Q, E) none of above
3) For the circuit shown in the figure, I = 0.50 A and R = 12 Ω. What is the value of the emf ε?
A) 18 V
B) 24 V
C) 6.0 V
D) 12 V
E) 48 V
4) When a potential difference of 10 V is placed across a certain solid cylindrical resistor, the current through it is 2
A. If the solid is stretched such that the length is twice as long as the original and the total volume remains the same,
the current will be
A) 8 A, B) 1/4 A, C) 1/2 A , D) 1 A, E) 4 A.
For the next two problems, consider a multi-loop circuit shown in the figure. It is not necessary to solve the entire
circuit.
5) What is current I1?
A, E) none of above.
A) A, B) 7A, C) A, D)
6) Assuming the polarity shown in the figure, the emf ε1 is closest to
A) -62 V,
B) 62 V, C) 22 V,
D) -22V, E) none of above.
(For the next two problems) Consider the circuit shown below, and the switch S has been open for a long time.
7) What is the potential difference Vab = Va-Vb ?
A) 0.00 V, B) 6V, C) 9V,
D) 18V, E) none of above
8) Long time after S has been closed, the energy on the 6 uF capacitor is
related to the energy on the 3 uF capacitor by U6uF/U3uF
A) ,
B) ,
C) 4,
D) 8,
E) 1
9) The figure shows a velocity selector that can be used to measure the speed of a charged particle. A beam of
particles is directed along the axis of the instrument. A parallel plate capacitor sets up an electric field E, which is
oriented perpendicular to a uniform magnetic field B. If the plates are separated by 2.0 mm and the value of the
magnetic field is 0.60 T, what voltage between the plates will allow particles of speed 5.0 × 105 m/s to pass straight
through without deflection?
A) 600 V
B) 1900 V
C) 3800 V
D) 190 V
E) 94 V
10) A particle of mass m with charge 2 C initially moves at v= (3 ̂ + 4 ĵ +5
field
10 , find the magnetic force vector on the particle.
A) (80 î + 60 ĵ ) N
B) (80 î - 60 ĵ ) N
C) (-80 î + 60 ĵ ) N
D) (-80 î - 60 ĵ ) N
E) None of above
) m/s. If it encounters a magnetic
11) The charge moves in a helical path, what is the separation between the successive helix?
A)
B)
C)
√
D)
E) none of above
12) A semicircular ring of radius R with a current I flowing counter-clockwise, as shown, is inside a magnetic field
=B .
What is the magnetic force acting on the semicircular (curved) part of the semi-loop?
A) 2RIB ̂
B) -2RIB ̂
C) 2RIB
D) -2RIB
13) What is the magnetic moment of the semi‐loop ? A) B) C) D)
E) 0 14) What is the torque acting on the semi‐loop ? A) ̂ B)
̂ C) ̂ D) ̂ E) 0 E) 0
15) (30pt ) A cylindrical capacitor consisting of two conducting shells of radius a and b and length h, are
charged with Q and –Q, respectively(assuming h is much larger than a and b).
a) Find the electric field everywhere(r<a, a<r<b, r>b).
b) Find the electric energy contained within a thin cylindrical shell of radius r (a<r<b) and thickness dr
and length h.
c) Find the total electric field energy.
d) Find the capacitance of the capacitor.
a) Using Gauss’s law the electric field can be calculated 0,
,
2
0,
b) The energy contained by the electric field in a cylindrical shell is given by dU=uedV 1
2
1
2
2
4
ln
c) The total electric energy d) The capacitance of the capacitor can be calculated by using , The capacitance can also be calculated by using C=Q/V, where