Physics 102. Second Midterm Examination. Summer Term ( ) (Fundamental constants) (Coulomb constant)

Transcription

1 ε µ0 N mp T kg Kuwait University hysics Department hysics 0 Secnd Midterm Examinatin Summer Term (00-0) July 7, 0 Time: 6:00 7:0 M Name Student N Instructrs: Drs. bdel-karim, frusheh, Farhan, Kkaj, a, azee, and Sharma 9 k N.m 4πε ο π 0.m/ -9 e g 9.8 m/s - me 9. 0 / / (N m (Fundamental cnstants) (ulmb cnstant) ) (ermittivity f free space) (remeability f free space) (Elementary unit f charge) (vgadr s number) (cceleratin due t gravity) (Electrn mass) kg refixes f units - m 0 k 0-6 µ 0 6 M 0 Fr use by Instructrs nly -9 n 0 9 G 0 (rtn mass) - p 0 T 0 rb Ttal Marks Ques Ttal Marks Imprtant Ntes:. D nt start yur exam until yu are tld t d s.. nswer all prblems, shw all yur wrk and mark yur final answer.. Yur wrk in this bklet shuld be neatly presented. 4. Bks, ntes and mbile phnes are nt allwed during the exam. 5. Yu may use a nn-prgrammable calculatr. Gd Luck

2 and is. current f 0.50 is passed thrugh a lamp fr.0 minutes using an ideal battery. If the energy dissipated in the lamp during this time is 540 J, find the terminal vltage f the battery. [ ints] w 540 W t 80 V 6. 0V I. s shwn in the figure an emf f εε 65 V is applied acrss an air-filled capacitr f capacitance.6 0 F. gemetrically identical capacitr is filled with a dielectric f dielectric cnstant KK.56 and is initially uncharged. The switch S is clsed fr a lng time. Hw much charge have passed thrugh the switch S? Take KK fr air. [ ints] K F S Q ε εε 65 V. 00-meter lng cpper wire cnnects pints and B. The electric ptential at B is 50 V less than that at pint. If the resistivity f cpper is Ωm, find the magnitude and directin f the current density in the wire. [4 ints] V VB EL E 0. 5 v m 7 J E.47 0 ρ m frm twards B. 4. The figure shws a fur capacitr arrangement that is cnnected t a circuit at pints and B. The capacitances are 0 µf0t 4 0 µf0t. The charge n 0T 0 µ0t.

3 What is the magnitude f the ptential difference VV VV BB 0T? [6 ints] Q Q Q Q Equivalent capacitances: 0 µ F 40 µf 4 B Q Q + Q Q 90 µ Equiv. capacitance f arrangement: 4 0 eq µ F Q eq Q 90 µ Qeq 90 7 V VB 5. 5V 0 eq 4 [Nte a sl. With V B V 5.5 is equally acceptable] 5. In the circuit shwn, find the value f the resistr that makes the current in the kω resistr equal t zer. [4 ints] V ab V I 9 0. m 4k 75 Ω I I 0. 75mas shwn V 8 8kΩ I 0.75m V k Ω + I 0 4k Ω a + 9 V I I + 8 V b 6. The circuit in the figure cnsists f an ideal battery with emf εε V, tw resistrs with resistances 4 Ω, 6 Ω and an initially uncharged capacitr with capacitance 6 µf. The switch S is clsed at time tt 0. Find the ptential difference acrss the capacitr at tiem tt s. [4 ints] apacitr is charged thrugh by emf ɛ. t V ε e s ( e ) 0. V V 4 εε + - S 7. Find the ptential difference VV aaaa between pints a and b shwn in the circuit belw. [5 ints]

4 eeee 5 Ω II II II VV aaaa V I a I 5 Ω 0 Ω 0 Ω 0 Ω 0 Ω I 5 Ω b 50 V 8. It is desired t find the ptential at a pint n the symmetry axis f a disc f radius with unifrmly distributed surface charge f density σσ. Fr this purpse ne can divide the disc int cncentric rings and ne such ring is shwn in the figure. If the pint is at a distance xx frm the centre and with the ptential taken t be zer at infinity: [5 ints] a) Find the ptential due t a ring f inner radius rr and uter radius rr + dddd. dv 4πε π rσ dr σ r ( r + x ) ε ( r + x ) dr xx b) Write the net ptential at in the frm f an integral. r+dr rr + dddd rr V σ ε r dr ( r + x ) c) alculate the integral in part b. V σ ε ( r + x ) ( + x ) σ x ε nceptual Questins

5 . The electric ptential inside a parallel plate capacitr a) is cnstant. b) increases linearly frm the negative t the psitive plate. (ans) c) decreases linearly frm the negative t the psitive plate. d) decreases inversely with the distance frm the negative plate. e) decreases inversely with square f the distance frm the negative plate.. wire is stretched unifrmly t 4-times its riginal length. If the vlume f the wire remains cnstant, its resistance changes by a factr f: a) /6 b) /4 c) d) 4 e) 6 (ans). parallel-plate capacitr is charged and remved frm the battery. When the plates are pulled further apart, which ne f the fllwing decreases? a) Electric field between the plates b) harge c) apacitance (ans) d) Vltage between the plates e) Energy stred in the capacitr 4. The figure belw shws three cylindrical cpper cnductrs alng with their face areas and lengths. When the same ptential difference V is applied acrss their lengths, which statement is crrect fr the currents thrugh them? a) I < I < I (ans) b) I < I < I l.5 l l c) I < I < I d) I < I < I () e) I < I < I () () 5. When a capacitr is discharged thrugh a resistr, which ne f the fllwing is false?

6 a) The electrical energy stred in the capacitr is cnverted int heat. b) The current in the capacitr is equal t the current in the resistr. c) The capacitr vltage decreases by half after a time equal t. (ans) d) The vltage acrss the capacitr equals the vltage acrss the resistr. e) The current in the circuit takes an infinite time t reach zer. 6. When a steady current passes thrugh the cnductr shwn belw, which statement is crrect fr the currents, drifts velcity f electrns and current densities at surfaces and? a) II > II, vv dd > vv dd and JJ JJ. b) II II, vv dd vv dd and JJ > JJ. c) II > II, vv dd > vv dd and JJ < JJ. d) II II, vv dd < vv dd and JJ < JJ. (ans) e) II II, vv dd > vv dd and JJ < JJ. 7. Which statement is crrect abut the real battery with internal resistance r in this circuit? a) The emf is smaller than the terminal vltage when switch S is clsed. b) The emf is the same as the terminal vltage when switch S is clsed. r c) The emf is the same as the terminal vltage when switch S is pen. (ans) ɛ + d) The emf is larger than the terminal vltage when switch S is pen. e) The emf is smaller than the terminal vltage when switch S is pen. S 8. In the tw circuits shwn belw the resistrs and batteries are identical. What is the rati f pwer dissipatin in circuit t that f circuit? a) 9 (ans) b) c) d) / e) /9 + + () ()