Conceptual Practice Problems for PHYS 1112 In-Class Exam #2A+2B

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1 Conceptual ractice roblems for HYS 1112 In-Class xam #2A+2B Thu. Mar. 19, 2009, 11:00am-12:15pm and 2:00pm-3:15pm C 2.01: In a two-source interference experiment two sources are oscillating in phase with the same period. The first intensity minimum, closest to the central intensity maximum M and to the left of M, is located at point, as shown in Fig A wave crest A from source 1 and a wave trough B from source 2 arrive simultaneously at. Therefore, A and B must have departed from their respective sources as follows: Fig M Source 1 Source 2 A departed 1/2 period before B. B departed 1/2 period before A. A departed 1 period before B. B departed 1 period before A. () A departed 3/2 period before B. C 2.01 Answer: C 2.02: A diffaction grating is illuminated with coherent (laser) light with a wavelength λ < d where d is the spacing between adjacent slits in the grating. The first intensity maximum, to the right of and closest to the central intensity maximum M, is located at point Q, as shown in Fig A wave crest A from slit R and a wave crest B from the neighboring slit S to the right of R, arrive simultaneously at Q. Therefore, A and B must have departed from their respective slits as follows: 1

2 Fig M Q R S Diff. Grating Laser Beam A departed 1/2 period before B. B departed 1/2 period before A. A departed 1 period before B. B departed 1 period before A. () A departed 3/2 period before B. C 2.02 Answer: C 2.03: A beam of coherent (laser) light of wavelength λ is incident upon a diffraction grating with line spacing d as shown in Fig The distance y (in cm) between the two 1st order intensity maxima, observed on a screen at a distance L on the other side of the grating, will 1st order maxima Δy Fig Screen L Diff. Grating Laser Beam decrease if we increase L decrease if we increase λ 2

3 increase if we decrease λ increase if we increase d () decrease if we increase d C 2.03 Answer: () C 2.04: A beam of coherent (laser) light of wavelength λ is incident upon two parallel slits with a spacing d as shown in Fig The distance y (in cm) between the two adjacent dark fringes (interference intensity minima), observed closest to the central maximum on a screen at a distance L on the other side of the slits, will 1st dark fringes Δy Fig Screen L Double Slit Laser Beam increase if we increase L increase if we decrease λ decrease if we increase λ increase if we increase d () decrease if we decrease d C 2.04 Answer: C 2.05: If two charges q 1 and q 2 at some distance r repel each other with a force of 160N, what force would they exert on each other if r is quadrupled ( 4); and q 1 and q 2 are unchanged? The two charges will repel each other with a force of 22µN attract each other with a force of 10N repel each other with a force of 10N attract each other with a force of 65000MN () repel each other with a force of 65000MN 3

4 C 2.05 Answer: C 2.06: If two charges q 1 and q 2 at some distance r attract each other with a force of 10N, what force would they exert on each other if q 1 is quadrupled ( 4) and its sign is reversed; and q 2 and r are unchanged? The two charges will repel each other with a force of 40N attract each other with a force of 2.1mN repel each other with a force of 2.1mN attract each other with a force of 56000MN () repel each other with a force of 56000MN C 2.06 Answer: C 2.07: If two charges q 1 and q 2 at some distance r attract each other with a force of 6N, what force would they exert on each other if q 1 is doubled ( 2) without changing its sign; q 2 is tripled ( 3) and its sign is reversed; and r is unchanged? The two charges will repel each other with a force of 1N attract each other with a force of 1N repel each other with a force of (1/6)N attract each other with a force of (1/6)N () repel each other with a force of 36N C 2.07 Answer: () C 2.08: If two charges q 1 and q 2 at some distance r repel each other with a force of 4.5N, what force would they exert on each other if q 1 is unchanged; q 2 is doubled ( 2) and its sign is reversed; and r is tripled ( 3)? The two charges will repel each other with a force of 1N attract each other with a force of 1N repel each other with a force of (1/6)N attract each other with a force of (1/6)N () repel each other with a force of 36N C 2.08 Answer: C 2.09: Q in Fig is positive point charge. Which arrow drawn at could correctly represent the electric field vector generated by Q at? 4

5 Fig () Q () C 2.09 Answer: C 2.10: Q in Fig is negative point charge. Which arrow drawn at could correctly represent the electric field vector generated by Q at? Fig Q () () C 2.10 Answer: C 2.11: Q 1 and Q 2 in Fig are positive point charges. Which arrow drawn at could correctly represent the total electric field vector generated by Q 1 and Q 2 at? 5

6 Fig Q 2 () Q 1 () C 2.11 Answer: () C 2.12: Q 1 in Fig is a positive point charge, and Q 2 is a negative point charge. Which arrow drawn at could correctly represent the total electric field vector generated by Q 1 and Q 2 at? Fig Q 2 () Q 1 () C 2.12 Answer: C 2.13: In xperiment 1 a proton travels from point A to point B, in the electric field generated by/between two oppositely charged capacitor plates, as shown in Fig In xperiment 2 an electron travels from point A to point B, in the same electric field between the same two charged capacitor plates. A proton has a charge +e and an electron has a charge e. 6

7 Fig B A Assume the proton experiences a drop in electric potential, V = 250V, and a loss of potential energy, U = 40aJ (where 1aJ J), in traveling from A to B. What will the electron experience? V = 500V and U = 80aJ V = 1000V and U = 160aJ V = +1000V and U = +160aJ V = 1000V and U = +160aJ () V = 250V and U = +40aJ C 2.13 Answer: () C 2.14: In xperiment 1 an electron travels from point A to point B, in the electric field generated by/between two oppositely charged capacitor plates, as shown in Fig In xperiment 2 a proton travels from point A to point B, in the same electric field between the same two charged capacitor plates. A proton has a charge +e and an electron has a charge e. Fig A B Assume the electron experiences a rise in electric potential, V = +250V, and a loss of potential energy, U = 40aJ (where 1aJ J), in traveling from A to B. What will the proton experience? V = +250V and U = +40aJ V = 100V and U = 16aJ V = +100V and U = +16aJ V = 100V and U = +16aJ () V = 50V and U = 8aJ C 2.14 Answer: 7

Solutions to Conceptual Practice Problems PHYS 1112 In-Class Exam #2A+2B

Solutions to Conceptual Practice Problems PHYS 1112 In-Class Exam #2A+2B Solutions to Conceptual ractice roblems HYS 1112 In-Class xam #2A+2B Thu. Mar. 19, 2009, 11:00am-12:15pm and 2:00pm-3:15pm C 2.01: In a two-source interference experiment two sources are oscillating in