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Ch. 25 - Electric Current and Resistance
Giancoli Douglas - Physics for Scientists and Engineers 5th edition
Giancoli Douglas5th editionPhysics for Scientists and EngineersISBN: 9780137488179Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoGiancoli Douglas 5th editionCh. 25 - Electric Current and ResistanceProblema 37
Capitolo 24, Problema 37

At \$0.12/kWh, what does it cost to leave a 25-W porch light on day and night for a year?

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1
Determine the total energy consumed by the porch light in one year. Start by calculating the power usage in kilowatts: \( P = \frac{25}{1000} \, \text{kW} \).
Calculate the total time the light is on in one year. Since the light is on day and night, the total time is \( t = 365 \times 24 \, \text{hours} \).
Find the total energy consumed by multiplying the power by the time: \( E = P \times t \).
Determine the cost of the energy consumed by multiplying the total energy \( E \) by the cost per kilowatt-hour: \( \text{Cost} = E \times 0.12 \).
Substitute the values into the equations and simplify to find the total cost of leaving the light on for a year.

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Concetti chiave

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Power Consumption

Power consumption is the rate at which an electrical device uses energy, measured in watts (W). In this case, the porch light consumes 25 watts, which indicates how much energy it uses per hour. Understanding power consumption is essential for calculating the total energy used over time.
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Power

Energy Cost Calculation

Energy cost calculation involves determining the total cost of electricity consumed by a device over a specific period. This is typically calculated by multiplying the power consumption (in kilowatts) by the time (in hours) the device is used and the cost of electricity per kilowatt-hour (kWh). This concept is crucial for finding the annual cost of running the porch light.
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Time Conversion

Time conversion is the process of converting time units to facilitate calculations. In this scenario, the light is on continuously for a year, which requires converting years into hours for accurate energy consumption calculations. There are 8,760 hours in a year (24 hours/day × 365 days/year), which is necessary for determining the total energy used by the light.
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Unit Conversions
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