Exam integers and Sequences Physics

PHYS0B1/PHYS1B1 SET B Do not write in the margin

Constants and integrals

c = 3 × 108 m.s-1 h = 6.626  10−34 J.s me = 9.1  10−31 kg mp = 1.67  10−27 kg
NA = 6 × 1023 particle/mol qe = 1.6 × 10−19 C ε0 = 8.85 × 10−12 C2.(N.m)−2
k = 9.0  109 N.m2/C2 −7
μ0 = 4π × 10 T.m.A −1
𝒅𝒙 𝒙 𝒅𝒙 𝒙 𝒅𝒙
∫ (𝒂𝟐+𝒙𝟐)𝟑/𝟐 = 𝟐 𝟐 𝟐; ∫ = 𝐥𝐧 (𝒙 + √𝒂𝟐 + 𝒙𝟐 ); ∫ 𝟐 𝟐 = √𝒂𝟐 + 𝒙𝟐
𝒂 √𝒂 +𝒙 √(𝒂𝟐 +𝒙 )
𝟐 √(𝒂 +𝒙 )
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QUESTION 1 [20]

1.1) 1.2) 1.3) 1.4) 1.5)
1.6) 1.7) 1.8) 1.9) 1.10)

1.1) Two identical small, charged spheres are a certain distance apart, and each one initially
experiences an electrostatic force of magnitude F due to the other. With time, charge gradually
leaks off of both spheres. When each of the spheres has lost half its initial charge, the magnitude
of the electrostatic force will be
A) 1/16 F.
B) 1/8 F.
C) 1/4 F.
D) 1/2 F.
E) None of the above.



1.2) The figure shows two unequal point charges, q and Q, of opposite sign. Charge Q has
greater magnitude than charge q. In which of the regions X, Y, Z will there be a point at which
the net electric field due to these two charges is zero?




A) only regions X and Z
B) only region X
C) only region Y
D) only region Z
E) all three regions




1.3) Two very large parallel sheets a distance d apart have their centers directly opposite each
other. The sheets carry equal but opposite uniform surface charge densities. A point charge that
is placed near the middle of the sheets a distance d/2 from each of them feels an electrical force
F due to the sheets. If this charge is now moved closer to one of the sheets so that it is a distance
d/4 from that sheet, what force will the charge experience?


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,PHYS0B1/PHYS1B1 SET B Do not write in the margin

A) 4F
B) 2F
C) F
D) F/2
E) F/4




1.4) A conducting sphere of radius R carries an excess positive charge and is very far from any
other charges. Which one of the following graphs best illustrates the potential (relative to
infinity) produced by this sphere as a function of the distance r from the center of the sphere?
A)




B)




C)




D)




E)




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, PHYS0B1/PHYS1B1 SET B Do not write in the margin

1.5) The electric field between square the plates of a parallel-plate capacitor has magnitude E.
The potential across the plates is maintained with constant voltage by a battery as they are
pulled apart to twice their original separation, which is small compared to the dimensions of
the plates. The magnitude of the electric field between the plates is now equal to
A) 4E.
B) 2E.
C) E.
D) E/2.
E) E/4.



1.6) A horizontal wire carries a current straight toward you. From your point of view, the
magnetic field at a point directly below the wire points
A) directly away from you.
B) to the left.
C) to the right.
D) directly toward you.
E) vertically upward.



1.7) An electron, moving toward the west, enters a uniform magnetic field. Because of this field
the electron curves upward. The direction of the magnetic field is
A) towards the north.
B) towards the south.
C) towards the west.
D) upward.
E) downward.




1.8) Two long parallel wires placed side-by-side on a horizontal table carry identical size
currents in opposite directions. The wire on your right carries current toward you, and the wire
on your left carries current away from you. From your point of view, the magnetic field at the
point exactly midway between the two wires
A) points upward.
B) points downward.
C) points toward you.
D) points away from you.
E) is zero.




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