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# Sample Final Exam

By Suzanne Flores,2014-09-30 04:36
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Sample Final Exam

OSBPHYSICS DEPARTMENT - KFUPM

Review: Chapter 24: Gauss’ Law

Q1. A cone with a circular base of radius 2.00 cm and height 3.00 cm is situated in a uniform 4 oelectric field of magnitude 3.5x10N/C making an angle of 40 with the perpendicular to

the base. What is the electric flux through the curved surface of the cone ? There is no

charge inside the cone. (ANS: 33.7 2Nm/C)

Q2. Two charged concentric cylinders of infinite length have radii 4.00 and 6.00 cm. The charge -6per unit length on the inner cylinder is 2.0 x 10 c/m and that on the outer cylinder is 2.0 -6 x 10C/m. Find the electric field at a point 5.0 cm from the axis of the cylinders. 5 (ANS: 7.21*10

N/C)

Q3. The intensity of the earth’s electric field near its surface is 130 N/C, pointing toward the

center of the earth. What is the charge on the earth, assuming it is uniformly distributed? 6Radius of the earth may be taken to be 6.4 x 10 m. (ANS: - 5.92 5* 10 C)

Q 4. What is the electric field between two parallel infinite planes of charge, one with a charge -72 -72per unit area of 6.00 x 10 c/m and the other with a charge per unit area of 9.0 x 10 c/m? 4 (ANS: 1.7 x 10

N/C)

Q5. A conducting spherical shell of radius 10 cm carries a net charge of 2.0 microcoulombs

uniformly distributed on its surface. Find the electric field at a point 15cm from the center 5of the shell. (ANS: 8. 0 x 10 N/C,

3Q6. A square sheet of copper of sides 20 cm is placed in an extended electric field of 5 x 10 N/C

directed perpendicular to the sheet. Find the charge density of each face of the sheet. -82 (ANS: 4. 43 x 10 C/m)

Q7. A solid conducting sphere of radius “a” has a net positive charge of 3*Q. Concentric with

this sphere is a thin conducting spherical shell of radius b (b>a) which has a net negative 2charge of magnitude Q. Find the electric field at a distance r>b. (ANS: Q / (2 ;r) o

Q8. A point charge Q is placed at the center of an uncharged hollow conducting sphere. The

inside radius of the sphere is “a” and the outside radius is “b”. What is the induced charge

per unit area on the inner surface of the hollow sphere? (ANS: -2Q/(4 * * a))

-8Q9. A small sphere whose mass is 0.001 kg carries a charge of 9.8 x 10 C. It hangs from a silk

thread that makes an angle of theta degrees (see Fig) with the surface of a large, charged, -72non-conducting sheet. If the charge density is uniform and equal to 6.64 x 10 C/m,

calculate the angle theta. (ANS: 20.

6 degrees)

Q10. A cube with sides of 0.2 m has its center at the origin of a rectangular coordinate frame.

Its faces are perpendicular to the coordinate axes. The electric field strength is E=100 * x

I N/C, where “x” is in m. Find the amount of charge within the cube. (ANS:

7.1*10** (-12) C )

-7=6.64*10 C/m2

m = 0.001 kg -8q = 9.8*10 C

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