BackA 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)?
A 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. 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?
It seems hard to justify spending \$5.00 for an LED lightbulb when an ordinary incandescent bulb costs 50¢. To see if this makes sense, compare a 60 W incandescent bulb that lasts 1000 hours to a 10 W LED bulb that has a lifetime of 15,000 hours. Both bulbs produce the same amount of visible light. If electricity costs \$0.15/kWh, what is the total cost—purchase price plus energy—to get 15,000 hours of light from each type of bulb? This is called the life-cycle cost.
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.]
In 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.
Two resistors, and , are connected in series to a constant voltage source such that . Which resistor dissipates more power?
When a resistor with resistance is connected to a -V flashlight battery, the resistor consumes W of electrical power. (Throughout, assume that each battery has negligible internal resistance.) What power does the resistor consume if it is connected to a -V car battery? Assume that remains constant when the power consumption changes.
An 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?
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.
A -watt light bulb is designed to operate at a voltage of volts. What is the operating resistance of the bulb?
In a circuit, a current of flows through a resistor of resistance . What is the total rate at which electrical energy is dissipated in the resistor?
In a -volt circuit, ten identical light bulbs each rated at watts are connected in parallel. What is the total current (amperage) drawn by the circuit?
Which quantity in a circuit is defined as the amount of work being done per unit of time?
A 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?