Idea Transcript
Final Exam Name :
Date :
Level : Physics I
Teacher : Kim
Q=ne E=k
1electron(e-) = -1.6×10-19C
1proton(e+) = +1.6×10-19C
[N/C] or E = [N/C] where k= 9×109 N·m²/C
I=
Fe = k
[A]
I=
[N]
[A]
You must show your work! Just writing down the answer is zero credit! 1. An ion loses 5 electrons. What is the charge on this ion? a) q = -8.0×10-19C b) q = -6.4×10-19C c) q = +8.0×10-19C d) q = +6.4×10-19C
ans) c 2. A calcium ion(Ca2+) and an aluminum ion(Al3+) exert an electrostatic force of repulsion on each other with a magnitude of 3×10-28N. How far apart are these ions? a) 0.2m b) 2.1m c) 4.2m d) 6.2m
ans) b 3. The electrostatic force of attraction between two charged objects is F. What would be the force between the objects if the charge on each of the objects were doubled and distance between the charges was doubled? a) F b) 2F c) 4F d) 8F
ans) a 4. The uranium nucleus contains a charge 92 times that of the proton. If a proton is shot at the nucleus, how large a repulsive force does the proton experience dues to the nucleus when it is 1×10-11m from the nucleus? a) 1.1 ×10-4N b) 2.1 ×10-4N c) 1.1 ×10-2N d) 2.1 ×10-2N
ans) b
Q=ne E=k
1electron(e-) = -1.6×10-19C
1proton(e+) = +1.6×10-19C
[N/C] or E = [N/C] where k= 9×109 N·m²/C
I=
Fe = k
[A]
I=
[N]
[A]
5. A conducting sphere has a net charge of –4.8×10-17C. What is the approximate number of excess electrons on the sphere? (a) 100 (b) 200 (c) 300 (d) 400 (e) 500
ans) c 6. Three point charges are placed at the following pints on the x-axis: q1= +2×10-6C at x=0, q2= -3×10-6C at x=0.4m and q3= -5×10-6C at x=1.2m. Find the force on the q3
q1
q2
q3 x(m)
ans) 0.148N 7. Three point charges, each of the same magnitude, with varying signs are arranged at the corners as shown. Which of the arrows labeled A, B, C and D gives the correct direction of the net forces that acts on the charges at the upper right corner? Justify your answer~! (a) A (b) B (c) C (d) D (e) the net force on that charge zero
B
D –q
+q A C
+q
ans) c
Q=ne E=k
1electron(e-) = -1.6×10-19C
1proton(e+) = +1.6×10-19C 9
[N/C] or E = [N/C] where k= 9×10 N·m²/C
I=
Fe = k
[A]
I=
[N]
[A]
y
8. Consider three point charges located as shown, where q1=q3= +5×10-6C, q2= +2×10-6C, and r = 0.1m.
q2 q3
x
i) Find the resultant force exerted on q3.
q1
ans) 24.2N ii) Find the angle the resultant force makes with respect positive x-axis
ans) 68° 9. Three charges are located along the x-axis as shown. The mass of the q2 is 4×10-9kg. The distance between q1 and q2 is 4m and the distance between q2 and q3 is 6m. Find the acceleration and the direction
+1.5×10-6C
-1.2×10-6C
q1
q2
of q2 when it is allowed to move if the other two charges remain fixed. (use a=
2×10-6C x(m) q3
)
ans) 1.03×105m/s2(left) 10. In a vacuum, two particles have charges of q1 and q2, where q1 = +3.5×10-6C. They are separated by a distance of 0.26m, and particle q1 experiences an attractive force of 3.4N. Find the charge of q2. a) +7.3×10-6C b) –7.3×10-6C c) +4.8×10-6C d) –4.8×10-6C
ans) b
Q=ne E=k
1electron(e-) = -1.6×10-19C
1proton(e+) = +1.6×10-19C
[N/C] or E = [N/C] where k= 9×109 N·m²/C
I=
Fe = k [A]
I=
[N] [A]
11. Two very small spheres are initially neutral and separated by a distance of 0.5m. Suppose that 3×1013 electrons are removed from one sphere and placed on the other. i) What is the magnitude of the electrostatic force that acts on each sphere? (ii) Is the force attractive or repulsive? Why? a) 0.83N, repulsive b) 0.43N, repulsive c) 0.83N, attractive d) 0.43N, attractive
ans) c 12. An electric field with a magnitude of 160N/C exists at a spot that is 0.15m away from a charge. At a place that is 0.45m away from this charge, what is the electric field strength? a) 17.8N/C b) 13.6N/C c) 10.4N/C d) 3.5N/C
ans) a 13. Two spheres are mounted on identical horizontal springs and rest on a frictionless table. When the spheres are uncharged, the spacing between them is 0.05m, and the springs are unstrained. When each sphere has a charge of +1.6×10-6C, the spacing doubles. Assuming that the spheres have a negligible diameter, determine the spring constants of the springs.
0.05m
hint; there are only two forces acting on the spheres, electrical force(Fe) and spring force(Fs= –kx : here 'k' is the spring constant. Do not be confused with the 'k' in F e=kQq/r2)
a) 109.5N/m
ans) b
b) 92.2N/m
c) 64.1N/m
d) 36.8N/m
Fe
Fs
Q=ne E=k
1electron(e-) = -1.6×10-19C
1proton(e+) = +1.6×10-19C
[N/C] or E = [N/C] where k= 9×109 N·m²/C
I=
14. An equilateral triangle has sides of 0.15m. Charges of q1= – 9×10-6C, q2= + 8×10-6C, and q3= +2×10-6C are located at the corners of the triangle. Find the magnitude of the resultant electrostatic force exerted on the q3. a) 2.45N b) 6.83N c) 11.4N d) 19.5
Fe = k [A]
I=
[N] [A]
q1
q2
q3
ans) b
15. A student performed an experiment in which the potential difference V between the ends of a long straight wire was varied. The current I in the wire was measured at each value of the potential difference with an ammeter and the results of the experiment are shown in the table below. Trial 1 2 3 4 5 6 7 8
V (volts) 5 10 15 20 25 30 35 40
I (amperes) 0.25 0.50 0.75 1.00 1.50 1.65 1.55 1.53
Which one of the following statements is the best conclusion based on the data? Justify your answer~! (a) The resistance of the wire is 20Ω. (b) The wire does not obey Ohm’s law. (c) The wire obeys Ohm’s law over the range of potential differences between 5 and 30V (d) The wire obeys Ohm’s law over the range of potential differences between 5 and 20V
ans) d