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1. 1. 2. 3. 4. 5. An electric device, which heats water by immersing a resistance wire in the water, generates 60 cal of heat per second when an electric potential difference of 11 V is placed across its leads. What is the resistance of the heater wire? (Note: 1 cal = 4.186 J) • {image} • {image} • {image} • {image} • {image}

2. What maximum power can be generated from an 11-V emf using any combination of a {image} - {image} resistor and a {image} - {image} resistor? • 31 W • 81 W • 53 W • 46 W • 70 W

3. How much energy is dissipated as heat during a two-minute time interval by a {image} resistor which has a constant 19-V potential difference across its leads? • 36 J • 18 J • 65 J • 71 J • 54 J

4. If {image} electrons pass through a {image} - {image} resistor in 12 min, what is the potential difference across the resistor? • 37 V • 23 V • 34 V • 25 V • 60 V

5. 1. 2. 3. 4. 5. A wire (length = 2.1 m, diameter = 1.2 mm) has a resistance of {image} . What is the resistivity of the material used to make the wire? • {image} • {image} • {image} • {image} • {image}

6. 1. 2. 3. 4. 5. A rod (length = 81 cm) with a rectangular cross section {image} has a resistance of {image} . What is the resistivity of the material used to make the rod? • {image} • {image} • {image} • {image} • {image}

7. If a mile of 24-gauge copper wire has a resistance of {image} and the resistivity of copper is {image} , what is the radius of the wire? (1 mile = 1.6 km) • 0.25 mm • 0.62 mm • 0.30 mm • 0.75 mm • 0.18 mm

8. A small bulb is rated at 6.0 W when operated at 110 V. Find its resistance (in ohms). • 0.33 • 6.0 • 18 • 1,800 • 2,000

9. The temperature coefficient of resistivity of iron is {image} ; that of carbon is {image} . An iron wire and a carbon rod, each having the same {image} resistance at {image} , are then cooled from that temperature to {image} . Find the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature. • -0.10 • +8.0 • +3.3 • -10 • +10

10. 1. 2. 3. 4. 5. The electron density in copper is {image} . The electron charge is {image} . When a 1.85 A current is present in a copper wire with a {image} cross-section, find the electron drift velocity, in m/s, with direction defined relative to the current density. • {image} • {image} • {image} • {image} • {image}

11. In the Drude model of electrical conduction, what quantity is the current density NOT directly proportional to? • the average time interval between successive collisions • the number of charge carriers per unit volume • the square of the electron charge • the electric field present in the wire • the resistivity of the wire

12. Light bulb {image} is rated at 25 W and light bulb {image} is rated at 60 W. Both are designed to operate at 220 V. Which statement is correct? • The 25 W bulb has a greater resistance and greater current than the 60 W bulb. • The 25 W bulb has a greater resistance and smaller current than the 60 W bulb. • The 25 W bulb has a smaller resistance and smaller current than the 60 W bulb. • The 25 W bulb has a smaller resistance and greater current than the 60 W bulb. • We need to know the resistivities of the filaments to answer this question.

13. Electric charge is conserved. As a consequence, when current arrives at a junction of wires, the charges can take either of two paths out of the junction and the numerical sum of the currents in the two paths equals the current that entered the junction. Thus, current is _____. • a vector • a scalar • neither a vector nor a scalar

14. A cylindrical wire has a radius {image} and length {image} If both {image} and {image} are doubled, the resistance of the wire _____. • increases • decreases • remains the same

15. When does a light bulb carry more current? • Just after it is turned on and the glow of the metal filament is increasing. • After it has been on for a few milliseconds and the glow is steady.

16. 1. 2. 3. 4. 5. Make an order-of-magnitude estimate of the cost of one person's routine use of a hair dryer for 5 years. If you do not use a blow dryer yourself, observe or interview someone who does. State the quantities you estimate and their values. • {image} • {image} • {image} • {image} • {image}