Additional Problems

| 100 | A cigarette lighter in a car is a resistor that, when activated, is connected across the 12-V battery. Suppose a lighter uses 33 W of power. Find (a) the resistance of the lighter and (b) the current that the battery delivers to the lighter.

| 101 | ssm Three capacitors (3.0, 7.0, and ) are connected in series. What is their equivalent capacitance?

| 102 | ssm A fax machine uses 0.110 A of current in its normal mode of operation, but only 0.067 A in the standby mode. The machine uses a potential difference of 120 V. (a) In one minute, how much more charge passes through the machine in the normal mode versus the standby mode, and (b) how much more energy is used?

| 103 | ssm In the Arctic, electric socks are useful. A pair of socks uses a 9.0-V battery pack for each sock. A current of 0.11 A is drawn from each battery pack by wire woven into the socks. Find the resistance of the wire in one sock.

| 104 | For the circuit shown in the drawing, find the current I through the 2.00-Ω resistor and the voltage V of the battery to the left of this resistor.

| 105 | In Section 12.3 it was mentioned that temperatures are often measured with electrical resistance thermometers made of platinum wire. Suppose that the resistance of a platinum resistance thermometer is when its temperature is 20.0°C. The wire is then immersed in boiling chlorine, and the resistance drops to . The temperature coefficient of resistivity of platinum is . What is the temperature of the boiling chlorine?

| 106 | The circuit in the drawing shows two resistors, a capacitor, and a battery. When the capacitor is fully charged, what is the magnitude q of the charge on one of its plates?

| 107 | A galvanometer with a coil resistance of and a full-scale current of 0.150 mA is used with a shunt resistor to make an ammeter. The ammeter registers a maximum current of 4.00 mA. Find the equivalent resistance of the ammeter.

| 108 | Multiple-Concept Example 9 discusses the physics principles used in this problem. Three resistors, 2.0, 4.0, and , are connected in series across a 24-V battery. Find the power delivered to each resistor.

* | 109 | ssm Eight different values of resistance can be obtained by connecting together three resistors (1.00, 2.00, and ) in all possible ways. What are they?

* | 110 | A resistor (resistance = R) is connected first in parallel and then in series with a resistor. A battery delivers five times as much current to the parallel combination as it does to the series combination. Determine the two possible values for R.

* | 111 | Interactive Solution 20.111 at provides one approach to problems like this one. Three resistors are connected in series across a battery. The value of each resistance and its maximum power rating are as follows: and 4.0 W, and 10.0 W, and and 5.0 W. (a) What is the greatest voltage that the battery can have without one of the resistors burning up? (b) How much power does the battery deliver to the circuit in (a)?

* | 112 | A and a resistor are connected in parallel. When this combination is connected across a battery, the current delivered by the battery is 0.294 A. When the resistor is disconnected, the current from the battery drops to 0.116 A. Determine (a) the emf and (b) the internal resistance of the battery.

* | 113 | ssm www A wire has a resistance of . It is melted down, and from the same volume of metal a new wire is made that is three times longer than the original wire. What is the resistance of the new wire?

* | 114 | One heater uses 340 W of power when connected by itself to a battery. Another heater uses 240 W of power when connected by itself to the same battery. How much total power do the heaters use when they are both connected in series across the battery?

* | 115 | ssm A sheet of gold foil (negligible thickness) is placed between the plates of a capacitor and has the same area as each of the plates. The foil is parallel to the plates, at a position one-third of the way from one to the other. Before the foil is inserted, the capacitance is C0. What is the capacitance after the foil is in place? Express your answer in terms of C0.

** | 116 | An aluminum wire is hung between two towers and has a length of 175 m. A current of 125 A exists in the wire, and the potential difference between the ends of the wire is 0.300 V. The density of aluminum is 2700 kg/m3. Find the mass of the wire.

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