Phys 121 Exam 3

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j = (ne) vd j = i/A V = iR P = iV P = i2R = V2/R series: Req = R1 + R2+..Rn parallel: Req= (1/R1+1/R2+..1/Rn)-1

RC-circuit: charging: Q = Q(1-e-t/RC), VC = V (1-e-t/RC), i = i0 (e-t/RC), VR = i0 R (e-t/RC),

discharging: Q = Q0 e-t/RC, i = i0 (e-t/RC), Vc = V0 (e-t/RC), VR = i0 R (e-t/RC),

Fm = qvxB Fe = qE Fm = iLxB v = E/B qΔ =Kf-KI K=½mv2 qvB = mv2/R R=mv/qB

 = xB  = NiA B wire, out = 0i/2R B wire, in = (0i/2R2)r Barc = 0i/4R Bloop = 0i/2R

Bsolenoid =0in Flux:  = BA emf = -d/dt emf = (2-1)/t emfmot = BLv emfmax = NAB

0 = 1.26x10-6 Tm/A e = 1.6x10-19 C me = 9.11x10-31kg

1 Two identical batteries of emf E=3Vand internal resistance r=0.4- are connected in parallel then connected in series with R=2- resistor. The current in the 2- resistor is:

A) 1.36 A

B) 1.85 A
C) 2.13 A
D) 2.95 A
E) 3.71 A

2. The power dissipated in the 2- resistor (in problem 2) is

A) 3.7 W

B) 6.9 W
C) 9.1 W
D) 17.3 W
E) 27.4 W

3. What is the current in a R = 0.5 resistor connected to a battery that has a - internal resistance when the potential drop across the terminals of the battery is -V when measured without any load?

A) 11

B) 18
C) 30
D) 48
E) none

4. For the RC circuit shown ( R = 1M, C = 5 F and  = 30 V) find the potential difference across the resistor 10 sec after the switch is closed.

A. 0.5 V

B. 1.5 V

C. 3.0 V

D. 3.5 V

E. 4.0 V

5. A portion of a circuit is shown, with the values of the currents given for some branches. What is the direction and value of the current i?

A) 6 up

B) 6 down
C) 1 up

D) 1 down

E) none

6. A particle with positive charge -C is a distance -m from a long straight wire that carries a current -A. The particle is traveling with speed v = 1000 m/s perpendicular to the wire. What are the direction and magnitude of the force on the particle if it is moving away from the wire? (in N)

A)1.0.10-8 up

B)1.0.10-8 down

C)2.0.10-8 up
D)2.0.10-8 down
E)2.0.10-7 up

7. An electric generator consists of turns of wire formed into a rectangular loop a = 0.05 m by b = 0.03 m placed entirely in a uniform magnetic field with magnitude -T. What is the maximum value of the emf produced when the loop is spun at rev/min about an axis perpendicular to B?

A)196.0

B)124.1

C)55.3
D)39.2
E)20.3

8.In the formula F = qvxB:

A)F must be perpendicular to v but not necessarily to B

B)F must be perpendicular to B but not necessarily to v

C)v must be perpendicular to B but not necessarily to F

D)all three vectors must be mutually perpendicular

E)none of the above

A positive particle (a proton) with charge 1.6.10-19C and mass 1.67x10-27 kg is moving with a velocity v=2.105 m/s in the positive z direction. A magnetic field B = 125.10-3 T is pointing in the positive y direction .

9. Find the force acting on the particle.

A)4 x 10-15 N, in the positive x-direction

B)4 x 10-15 N, in the negative x-direction

C)1.6 x 10-19 N, in the positive z-direction

D)1.6 x 10-19 N, in the negative z-direction

E)zero

10. Find the frequency of proton circular motion.

A)1.9 MHz

B)1.2 MHz

C)0.5 MHz
D)0.2 MHz
E)0.1 MHz

11. The magnetic field B = 0.5j is acting on proton moving in xy plane with velocity

v =105i +105j (in m/s). Find the force acting on the proton.

A)8 x 10-15 N, in the positive z-direction

B)8 x 10-15 N, in the negative z-direction

C)1.6 x 10-19 N, in the positive y-direction

D)1.6 x 10-19 N, in the negative y-direction

E)zero

12. Magnetic field B = 1 T goes out of the plane of the page. A straight wire carries a current 1 A from right to left. Find the direction of force acting on the wire.

A)out of the page

B)into the page

C)left, in the plane of the page

D)right, in the plane of the page

E)up, in the plane of the page

13. Two circular coils of equal radius 2 cm are placed several centimeters apart. If viewed from left, the current in the both loops is clockwise. The direction of magnetic field along the axis passing through the loops' centers and halfway

A)is to the right.

B)is to the left.

C)is oscillating.

D)zero

E)depends on the distance between coils

14. The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest.

A)1, 2, 3

B)3, 2, 1

C)1, 3, 2

D)2, 3, 1

E)2, 1, 3

Workout problems:

1.For the circuit shown find the magnitude of the current through each of the resistor if E=24 -V and R1 = 5  R2 = 10  and R3 = 15 

2. The wire shown in fig. carries current I = 5 A. If the R = 20 cm what net magnetic field B ( magnitude and direction) is produced at the center C of the semicircle by the entire wire?

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