Physics 72: Chapter 25 and 26 Problem Set Name: Lecturer: Mr Carlos Baldo III
Summer 2010 Score: Section: X7-7
Encircle the letter of the correct answer. Solve each problem clearly and completely for full credit. 1.
Voltage. In the circuit shown below, the voltmeter reading should be:
A. B. C. D. E. 2.
Resistivity. All of the statements below are true for resistivity except:
A. B. C. D. E. 3.
12 V 8V 10 V 24 V 48 V
It is ratio of the magnitudes of electric field and current density. It is zero for perfect conductors, and infinite for perfect insulators. It is the reciprocal of conductivity σ. It is a property of a material; unlike resistance, which is a property of geometry. It is a property that is present for Ohmic devices and absent for non-Ohmic devices.
Ohm’s Law. A current of 0.5A exists in a 60-Ω lamp. The applied potential difference is:
A. B. C. D. E.
15 V 30 V 60 V 120 V 1800V
4.
Power. A flat iron is marked “120 volt, 600 watt.” In normal use, the current through the iron is: A. 0.2 A B. 2 A C. 4 A D. 5 A E. 7.2 A
5.
Resistance. A steel trolley-car rail has a cross-sectional area of 3.0 x 10 m . What is the resistance of 1.0 x 10 m of rail? -7 The resistivity of the steel is 3.0 x 10 Ω-m. -2 A. 1.0 x 10 Ω 2 B. 1.0 x 10 Ω -2 C. (1/3) x 10 Ω 2 D. (1/3) x 10 Ω E. Cannot determine because temperature is not given.
6.
DC Circuit. Four 20-Ω resistors are connected in series and the combination is connected to a 20-V emf device. The current in any one of the resistors is: A. 0.25 A B. 1.0 A C. 4.0 A D. 5.0 A E. 100 A
7.
Kirchhoff’s Law. Consider the circuit on shown on the right. What is the current across R1? (R1 = R2 = 1 Ω ) A. 0 A B. 5 A C. 10 A D. 15 A E. None of the above
-3
2
6
Physics 72: Chapter 25 and 26 Problem Set 8.
9.
Resistance. Five cylindrical wires are made of the same material. Their lengths and radii are: Rank the wires according to their resistance, least to greatest. A. 1, 2, 3 Length B. 1, 3, 2 Wire 1 L C. 2, 1, 3 Wire 2 3L/2 D. 2, 3, 1 Wire 3 L/2 E. 3, 1, 2
Summer 2010
Radius r r/2 r/2
Effective. Consider N identical resistors arranged in groups of 3 as shown. What is the effective resistance across the end terminals A and B? A. Reff = 3 RN B. Reff = 2 RN C. Reff = RN D. Reff = (1/3) RN E. Reff = (1/2) RN
10. RC. A 2-nF capacitor is charged by connecting it in series to a 10-Ω resistor and a battery. After the capacitor is fully charged with maximum charge QMAX = 10 nC, the battery is disconnected from the circuit. What is current passing through the resistor immediately after the battery is removed? A. (1/2) A B. 1 A C. 2 A D. 5 A E. 10 A 11. Decay. Shown are the current versus time charging curves for 4 RC circuits with identical resistances (R) but different capacitances (C). Which of these circuits has the smallest capacitance value? Note: All circuits have the same initial current values.
12. RC Fully charged. After a long time such that the capacitor is fully charged, what is the current I passing through the battery?
B.
I=V/R1 I=V/R2
C.
I=V/ ( R1 +R2 )
D.
I=V ( R2 -R1 ) /R1 R2
E.
I=V ( R2 +R1 ) /R1 R2
A.
13. RC short. Consider the RC Circuit given below with R1 = 1kΩ, R2 = 3kΩ and C = 0.1pF. The constant battery source is equal to 12V. At t = 0, the switch is closed immediately, calculate the effective resistance of the circuit. A. 3 kΩ B. 5 kΩ C. 7 kΩ D. 9 kΩ E. 11 kΩ
Physics 72: Chapter 25 and 26 Problem Set
Summer 2010
14. Series-Parallel. A length of wire has a resistance of 1200-Ω. The wire is cut into N identical pieces which are then connected in parallel. The resistance of the parallel arrangement is 3-Ω. What is the value of N? A. 5 B. 10 C. 20 D. 30 E. 40 15. Line charge. Consider a ring with radius a and linear charge density λ rotating about its axis with angular velocity ω. The average current is _____. A. ωλ B. ωλ/a C. ωλa D. 2ωλa E. 2ωλ/a 16. Parallel-series. You have two identical resistors with individual resistance equal to R and an external potential source V. What is the ratio of the electric field for its series and parallel combinations? NOTE: Es is the field when the resistors are connected in series while Ep when they are connected in parallel. A. Ep = Es/4 B. Ep = Es/2 C. Ep = Es D. Ep = 2Es E. Ep = 4Es 17. Intense. Two different light bulbs A and B are connected in parallel across the same battery. Bulb A lights more brightly than bulb B. Which of the following is TRUE? Note: Bulbs are rated in terms of power. Higher power ratings give rise to brighter illumination and more expenses. A. VA > VB B. IA < IB C. RA < RB D. RA = RB E. RA > RB 18. Polarity. Two batteries of different voltages are connected in series with each other and an external load resistor. The current in the circuit is 3.0 amperes. If the polarity of one of the battery is reversed, the current is 1.0 ampere. The ratio of the voltage across the two batteries is _________. A. 3.0 B. 2.5 C. 2.0 D. 1.5 E. 1.0 19. Power. When two identical resistors are connected in series with the battery, the power delivered by the battery is 20 W. If these resistors are connected in parallel across the terminals of the same battery, what is the power delivered by the battery? A. 5 W B. 10 W C. 20 W D. 40 W E. 80 W
Physics 72: Chapter 25 and 26 Problem Set
Summer 2010
20. GPS works. A battery-powered global positioning system (GPS) receiver operating on 9.0V draws a current of 0.5A. How much electrical energy does it consume during 2 hours? A. 4.5 W-hr B. 9.0 W-hr C. 18.0 W-hr D. 36.0 W-hr E. 72.0 W-hr 21. Series. Two resistors are connected in series to a dc battery source as shown in the right. Letting I1 and I2 be the currents flowing through the resistors R1 = 1kΩ and R2 = 2kΩ respectively, which of the following is TRUE? A. |I1| > |I2| B. |I1| < |I2| C. |I1| = |I2| D. |I1| = -|I2| E. Depends to the battery’s internal resistance 22. Parallel. Two resistors are connected in parallel to a dc battery source as shown in the right. Letting I1 and I2 be the currents flowing through the resistors R1 = 1kΩ and R2 = 2kΩ respectively, which of the following is TRUE? A. |I1| > |I2| B. |I1| < |I2| C. |I1| = |I2| D. |I1| = -|I2| E. Depends to the battery’s internal resistance 23. A German Nickel wire with length L and cross sectional area A is connected to a constant battery source at a steady temperature. What happens to the current flowing through the wire if its length is TRIPLED but its diameter shrinks to HALF of its initial value? A. The current increases by a factor 6 B. The current increases by a factor 12 C. The current remains the same D. The current decreases by a factor 6 E. The current decreases by a factor 12 24. Dissipate. Two resistors dissipate the same amount of power. The potential drop across resistor A is four times than that across resistor B. If the resistance of B is R, what is the resistance of A? A. RA = (1/4) R B. RA = (1/8) R C. RA = 4 R D. RA = 8 R E. RA = 16 R 25. Loop rule. The correct KVL or loop equation for the outermost loop of the circuit shown at the right is ______________. A. 7V – (2Ω) I2 – (3Ω) I = 0 B. 7V – (2Ω) I2 + (3Ω) I = 0 C. 7V + (2Ω) I2 – (3Ω) I = 0 D. 17V – (2Ω) I2 – (3Ω) I = 0 E. 17V – (2Ω) I2 + (3Ω) I = 0
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