Physics (2): Midterm Exam

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PHYS 04 Form A Taiah University - Yanu Branch Faculty of Sciences and Arts at Yanu Department of Physics Physics (2): Midterm Exam Monday 02 nd May 20 AD, 28 th Jumada al-awwal 432 AH 6:00 a.

1 PHYS 04 Form A Taiah University - Yanu Branch Faculty of Sciences and Arts at Yanu Department of Physics Physics (2): Midterm Exam Monday 02 nd May 20 AD, 28 th Jumada al-awwal 432 AH 6:00 a.m to 8:00 a.m Duration of Exam: Two Hours Answer ALL questions in the answer sheet Electronic calculators may e used, provided that they cannot store text USE OF MOBILE PHONES IS STRICTLY PROHIBITED, EVEN AS CALCULATORS A list of relevant constants and equations is provided Each multiple-choice question is marked out of The total mark for this exam is 20

2 YOU MAY FIND THE FOLLOWING USEFUL F = qq ˆd d 2 F = k qq d 2, E = Q ˆd d 2 E = k Q d 2, F = q E, p = qd, from to τ = p E = pesinφˆn U = p. E = pecosφ Φ E = E.dA Φ E = q enc ǫ 0 V a = V a V = a V a = Ed(uniform field) E.d r E r = dv dr C = Q V =, Series C s C i C p = C i, Parallel I = dq dt V = IR R s = R i, Series =, Parallel R p R i P = IV I = 0 in a junction V = 0 in a loop I = I 0 exp(t/τ), charging τ = RC PHYSICAL CONSTANTS AND CONVERSION FACTORS SYMBOL DESCRIPTION NUMERICAL VALUE n nano 0 9 µ micro 0 6 m milli 0 3 e electric charge C ǫ 0 permittivity of free space C 2 N m 2 k N.m 2 /C 2

3 Multiple-choice questions Choose the correct answer for each question. The electric force etween two (identical) positive charges is (a) attractive () repulsive (c) neutral (d) zero 2. The unit of measurement of electric field is (a) C () N/C (c) N (d) m 3. The time constant of an RC circuit has units: (a) second/farad () second / Ohm (c) Farad/Ohm (d) second 4. The magnitude of the electric field produced y a single charge q = 0 6 C, measured at a distance d = 0. m from it is:.9 N/C () N/C (c) N/C (d) 90 N/C 5. The magnitude of the electric force etween two (identical) charges q = 0 6 C, separated y a distance d = 0. m is:.9 N () N (c) N (d) 90 N 6. Two resistors R = 4Ω and R 2 = 6Ω are attached in parallel. The equivalent resistance R p of the group is: (a) R p = 0Ω 2

4 () R p = 0.47Ω (c) R p = 2.4Ω (d) R p = 24Ω 7. Two capacitors C = 4 F and C 2 = 6 F are attached in parallel. The equivalent capacitance of the network C p is: (a) C p = 0 F () C p = 2.4 F (c) C p = 0.47 F (d) C p = 24 F 8. A cue encloses two charges C and 2 C. What is the total flux of electric field out of the cue? ().3 0 N m 2 /C (c).3 0 N m 2 /C (d) C 9. A conductor carries charge Q at equilirium. What is the electric field inside the conductor? (a) N/C () 0 (c) Q (d) Q/ 0. Four electric wires meet at a junction. The first carries 4 A into the junction, the second carries 5 A out of the junction, and the third carries 2 A out of the junction. The fourth carries: (a) 7 A out of the junction () 7 A into the junction (c) 3 A out of the junction (d) 3 A into the junction. A 200-N/C electric field is in the positive x-direction. The electric force on an electron of charge q = C in this field is: (a) 200 N in the positive x-direction () 200 N in the negative x-direction (c) N in the negative x-direction (d) N in the positive x-direction 3

5 2. A wire carries a steady current of I = 2 A. The charge that passes through a cross section of the wire in t = 2 s is: (a) Q = C () Q = C (c) Q = 4 C (d) Q = 2 C 3. For the network of resistors shown in figure, what is the equivalent resistance? Ω Ω a Ω Ω Figure : Question 3 (a) 4 Ω () 2 Ω (c) 0.5 Ω (d) Ω 4. In figure 2, the switch S is initially open. The am-metre reads 2.0 A. When the switch S is closed the current in the am-metre ecomes: 5Ω 70 V 20Ω 60Ω A S Figure 2: Questions 4-6 () A 4

6 (c) 2 A (d) 2.33 A 5. In figure 2 (with the switch S closed), what is the current in the 60Ω resistor? [Hint: You may first calculate the potential difference across the resistors 60Ω and 20Ω].58 A ().75 A (c) 2.33 A (d) 200 A 6. In figure 2 (with the switch S closed), what is the electric power consumption of the circuit? (a) 50 W () 63 W (c) 20 W (d) 75 W 7. In the circuit shown in figure 3, the capacitor is initially uncharged. At time t = 0, the switch S is closed. If τ denotes the circuit time constant, the approximate current through the 3 Ω resistor when t = τ/0 is: S 6Ω 6µ F 0 V 3Ω Figure 3: Question 7 (a).0 A () 0.38 A (c) 0.50 A (d) 0.75 A Questions 8-20: A spherical capacitor is made of a spherical conductor of radius a and charge Q, surrounded y a thin spherical shell of radius and charge Q (a < ) (see figure 4). The two spheres are concentric. The electric field is zero everywhere except in the region etween the conductors. 8. What is the magnitude of the electric field E(r) within the region a < r <? where r is the distance from the centre of the spheres. 5

7 a Figure 4: Questions 8-20 Q () r Q (c) r 2 Q (d) r 3 9. What is the electric potential difference across the capacitor: V a = a E(r)dr? You may assume that r 2dr = r. () (c) (d) ( Q ) a 3 ( 3 Q ) a 2 ( 2 Q a ) 20. What is the capacitance of the capacitor C = Q/V a (a) a/(a) () (a)/a (c) 0 (d) a a END OF EXAM 6

Review. Spring Semester /21/14. Physics for Scientists & Engineers 2 1

Review. Spring Semester /21/14. Physics for Scientists & Engineers 2 1 Review Spring Semester 2014 Physics for Scientists & Engineers 2 1 Notes! Homework set 13 extended to Tuesday, 4/22! Remember to fill out SIRS form: https://sirsonline.msu.edu Physics for Scientists &