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27. Resistors & DC Circuits

Power in Circuits

27. Resistors & DC Circuits

Power in Circuits

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Power in Circuits

Power in Circuits

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Electric Power (2 of 3) Example Problems

Electric Power (2 of 3) Example Problems

Step by Step Science

Electric Power (1 of 3) and Watts, An Explanation

Electric Power (1 of 3) and Watts, An Explanation

Step by Step Science

Basic Electricity - Power and watts

Basic Electricity - Power and watts

Electric power | Circuits | Physics | Khan Academy

Electric power | Circuits | Physics | Khan Academy

Khan Academy Physics

Practice this topic

Multiple Choice

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?

Has a video solution.

Multiple Choice

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?

Has a video solution.

Multiple Choice

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?

Multiple Choice

A 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?

Textbook Question

A 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?

Has a video solution.

Textbook Question

A 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?

Has a video solution.

Textbook Question

The 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.

Has a video solution.

Textbook Question

A 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?

Has a video solution.

Textbook Question

Electric 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?

Has a video solution.

Textbook Question

Consider the circuit of Fig. E25.30

. (c) At what rate is electrical energy being converted to other forms in the 8.0-V battery?

Has a video solution.

Textbook Question

Consider the circuit of Fig. E25.30

. (b) What is the power output of the 16.0-V battery?

Has a video solution.

Textbook Question

Consider 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?

Has a video solution.

Textbook Question

When 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.

Has a video solution.

Textbook Question

Consider 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.

Has a video solution.

Textbook Question

A 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?

Has a video solution.

Textbook Question

The 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?

Has a video solution.

Textbook Question

A 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?

Has a video solution.

Textbook Question

The 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.

Has a video solution.

Textbook Question

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. 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?

Has a video solution.

Textbook Question

The 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?

Has a video solution.

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