Multiple ChoiceA hair dryer operates at 120 V (the voltage produced by a household outlet), and outputs 1200 W of energy. For this problem, treat the hair dryer as a single resistor. (a) At what current does the hair dryer operate?(b) What is the resistance of the hair dryer?1958views16rank1comments
Multiple ChoiceAn incandescent lightbulb produces 100 W of light. If this lightbulb operates at 25% efficiency (meaning that out of all the power it generates, only 25% is released as light), what resistance must the lightbulb have if it operates at 120 V?720views23rank6comments
Multiple ChoiceA 1.4 kW toaster is connected to a wall outlet, which provides a potential difference of 120 V. What is the effective resistance of the toaster?249views
Multiple ChoiceA certain resistor is connected across a 9.0 V battery and dissipates 20 W of power. The battery is replaced with an 18 V battery. How much power is dissipated in the resistor now?261views
Textbook QuestionA typical small flashlight contains two batteries, each having an emf of 1.5 V, connected in series with a bulb having resistance 17 Ω. ((b) If the batteries last for 5.0 h, what is the total energy delivered to the bulb?469views
Textbook QuestionA typical small flashlight contains two batteries, each having an emf of 1.5 V, connected in series with a bulb having resistance 17 Ω. (a) If the internal resistance of the batteries is negligible, what power is delivered to the bulb?737views
Textbook QuestionThe battery for a certain cell phone is rated at 3.70 V. According to the manufacturer it can produce 3.15 * 10^4 J of electrical energy, enough for 5.25 h of operation, before needing to be recharged. Find the average current that this cell phone draws when turned on.700views
Textbook QuestionA heart defibrillator is used to enable the heart to start beating if it has stopped. This is done by passing a large current of 12 A through the body at 25 V for a very short time, usually about 3.0 ms. (b) how much energy is transferred?783views
Textbook QuestionElectric eels generate electric pulses along their skin that can be used to stun an enemy when they come into contact with it. Tests have shown that these pulses can be up to 500 V and produce currents of 80 mA (or even larger). A typical pulse lasts for 10 ms. What power and how much energy are delivered to the unfortunate enemy with a single pulse, assuming a steady current?323views
Textbook QuestionConsider the circuit of Fig. E25.30. (c) At what rate is electrical energy being converted to other forms in the 8.0-V battery?469views
Textbook QuestionConsider the circuit of Fig. E25.30. (b) What is the power output of the 16.0-V battery?303views
Textbook QuestionConsider the circuit of Fig. E25.30. (a) What is the total rate at which electrical energy is dissipated in the 5.0-Ω and 9.0-Ω resistors?497views
Textbook QuestionWhen a resistor with resistance R is connected to a 1.50-V flashlight battery, the resistor consumes 0.0625 W of electrical power. (Throughout, assume that each battery has negligible internal resistance.) (a) What power does the resistor consume if it is connected to a 12.6-V car battery? Assume that R remains constant when the power consumption changes.381views
Textbook QuestionConsider the circuit of Fig. E25.30 (d) Show that the power output of the 16.0-V battery equals the overall rate of consumption of electrical energy in the rest of the circuit.214views
Textbook QuestionA 1500-W electric heater is plugged into the outlet of a 120-V circuit that has a 20-A circuit breaker. You plug an electric hair dryer into the same outlet. The hair dryer has power settings of 600 W, 900 W, 1200 W, and 1500 W. You start with the hair dryer on the 600-W setting and increase the power setting until the circuit breaker trips. What power setting caused the breaker to trip?703views
Textbook QuestionThe heating element of an electric dryer is rated at 4.1 kW when connected to a 240-V line. (b) What is the resistance of the dryer's heating element at its operating temperature?376views
Textbook QuestionA 60 W lightbulb and a 100 W lightbulb are placed in the circuit shown in FIGURE EX28.9. Both bulbs are glowing. a. Which bulb is brighter? Or are they equally bright?99views
Textbook QuestionThe five identical bulbs in FIGURE EX28.11 are all glowing. The battery is ideal. What is the order of brightness of the bulbs, from brightest to dimmest? Some may be equal.112views
Textbook QuestionA small toaster that operates at 120 V has a heating element made from a 4.4-m-long, 0.70-mm-diameter nichrome wire. The resistivity, density, and specific heat of nichrome are, respectively, 1.5 x 10⁻⁶ Ωm, 8400 kg/m³, and 450 J/kg K. b. If half the heat energy is lost to the air, how long does it take the heating element to warm from 20℃ to 450℃, about the temperature at which it first begins to glow red?136views
Textbook QuestionThe flash on a compact camera stores energy in a 120 μF capacitor that is charged to 220 V. When the flash is fired, the capacitor is quickly discharged through a lightbulb with 5.0 Ω of resistance. b. At what rate is the lightbulb dissipating energy 250 μs after the flash is fired?272views
Textbook Question(II) A 12-V battery causes a current of 0.50 A through a resistor.(b) how many joules of energy does the battery lose in a minute?62views
Textbook Question(I) The heating element of an electric oven is designed to produce 3.1 kW of heat when connected to a 240-V source. What must be the resistance of the element?52views
Textbook Question(I) An electric car uses a 45-kW (160-hp) motor. If the battery pack is designed for 340 V, what current would the motor need to draw from the battery? Neglect any energy losses in getting energy from the battery to the motor.60views
Textbook Question(II) A 120-V hair dryer has two settings: 1250 W and 1875 W.(a) At which setting do you guess the resistance to be higher?After making a guess, determine the resistance at(b) the lower setting, and(c) the higher setting.26views
Textbook Question(II) You buy a 75-W lightbulb in Europe, where electricity is delivered at 240 V. If you use the bulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: Assume roughly that brightness is proportional to power consumed.]54views
Textbook Question(II) At $0.12/kWh, what does it cost to leave a 25-W porch light on day and night for a year?60views
Textbook Question(II) A power station delivers 750 kW of power at 12,000 V to a factory through wires with total resistance 3.0 Ω. How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?56views
Textbook Question(II) A traditional incandescent lamp filament may have been lit to a temperature of 2700 K. A contemporary halogen incandescent lamp filament may be at around 2900 K.(a) Estimate the percent increase in efficiency of the halogen bulb over the traditional one. [Hint: See Section 19–10.](b) To produce the same amount of light as a traditional 100-W bulb, estimate what wattage a halogen bulb should use.51views
Textbook Question(III) A 1.0-m-long round tungsten wire is to reach a temperature of 3100 K when a current of 18.0 A flows through it. What diameter should the wire be? Assume the wire loses energy only by radiation (emissivity ∊ = 1.0 , Section 19–10) and the surrounding temperature is 20°C.53views
Textbook Question(a) A particular household uses a 2.2-kW heater 2.0 h/day (“on” time), four 100-W lightbulbs 6.0 h/day , a 3.0-kW electric stove element for a total of 1.0 h/day, and miscellaneous power amounting to 2.0 kWh/day . If electricity costs $0.115 per kWh, what will be their monthly bill (30 d)?40views
Textbook QuestionThe current in an electromagnet connected to a 240-V line is 21.5 A. At what rate must cooling water pass over the coils for the water temperature to rise no more than 5.50 C°?49views
Textbook QuestionAn 1875-W hair dryer is designed for 117 V.(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.(b) How would the actual change in resistivity with temperature affect your answer?20views
Textbook QuestionA microwave oven running at 72% efficiency delivers 950 W to the interior. Find(a) the power drawn from the source, and56views
Textbook QuestionA microwave oven running at 72% efficiency delivers 950 W to the interior. Find(b) the current drawn. Assume a source voltage of 120 V.66views
Textbook QuestionDetermine the resistance of the tungsten filament in a 75-W 120-V incandescent lightbulb(a) at its operating temperature of about 2800 K,87views
Textbook QuestionA 100-W, 120-V incandescent lightbulb has a resistance of 12 Ω when cold (20°C) and 150 Ω when on (hot). Calculate its power consumption(a) at the instant it is turned on, and(b) after a few moments when it is hot.62views
Textbook QuestionIn an automobile, the system voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the car’s generator (or “alternator”) is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.44views
Textbook QuestionLightbulb A is rated at 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications.(a) What is the current through each bulb?48views
Textbook QuestionLightbulb A is rated at 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications.(b) What is the resistance of each bulb?50views
Textbook QuestionIf a wire of resistance R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source? Assume the wire’s volume and density remain constant.26views
Textbook QuestionAn electric heater is used to heat a room of volume 65m³ . Air is brought into the room at 5°C and is completely replaced twice per hour. Heat loss through the walls amounts to approximately 750 kcal/h. If the air is to be maintained at 22°C, what minimum wattage must the heater have? (The specific heat of air is about 0.17 kcal/kg •C° .)38views
Textbook Question(II) A voltage V is applied to n identical resistors connected in parallel. If the resistors are instead all connected in series with the applied voltage, show that the power transformed is decreased by a factor n² .58views
Textbook QuestionA flashlight bulb rated at 2.0 W and 3.0 V is operated by a 9.0-V battery. To light the bulb at its rated voltage and power, a resistor R is connected in series as shown in Fig. 26–81. What value should the resistor have?<IMAGE>91views
Textbook QuestionIn the circuit shown in Fig. 26–75, the 33-Ω resistor dissipates 0.80 W. What is the battery voltage?<IMAGE>80views
Textbook QuestionA 2800-W oven is connected to a 240-V source.(b) How long will it take to bring 150 mL of 15°C water to 100°C assuming 65% efficiency?66views
Textbook QuestionCopper wire of diameter 0.259 cm is used to connect a set of appliances at 120 V, which draw 1250 W of power total.(a) What power is wasted in 25.0 m of this wire?55views
Textbook QuestionA 2800-W oven is connected to a 240-V source. (a) What is the resistance of the oven’s heating elements?61views
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