# 9.5 Electrical energy and power  (Page 6/8)

 Page 6 / 8

The life spans of the three types of bulbs are significantly different. An LED bulb has a life span of 50,000 hours, whereas the CFL has a lifespan of 8000 hours and the incandescent lasts a mere 1200 hours. The LED bulb is the most durable, easily withstanding rough treatment such as jarring and bumping. The incandescent light bulb has little tolerance to the same treatment since the filament and glass can easily break. The CFL bulb is also less durable than the LED bulb because of its glass construction. The amount of heat emitted is 3.4 btu/h for the 8-W LED bulb, 85 btu/h for the 60-W incandescent bulb, and 30 btu/h for the CFL bulb. As mentioned earlier, a major drawback of the CFL bulb is that it contains mercury, a neurotoxin, and must be disposed of as hazardous waste. From these data, it is easy to understand why the LED light bulb is quickly becoming the standard in lighting.

Light output of led, incandescent, and cfl light bulbs
Light Output
(lumens)
LED Light Bulbs
(watts)
Incandescent Light Bulbs
(watts)
CFL Light Bulbs
(watts)
450 4−5 40 9−13
800 6−8 60 13−15
1100 9−13 75 18−25
1600 16−20 100 23−30
2600 25−28 150 30−55

## Summary of relationships

In this chapter, we have discussed relationships between voltages, current, resistance, and power. [link] shows a summary of the relationships between these measurable quantities for ohmic devices. (Recall that ohmic devices follow Ohm’s law $V=IR$ .) For example, if you need to calculate the power, use the pink section, which shows that $P=VI$ , $P=\frac{{V}^{2}}{R}$ , and $P={I}^{2}R$ .

Which equation you use depends on what values you are given, or you measure. For example if you are given the current and the resistance, use $P={I}^{2}R$ . Although all the possible combinations may seem overwhelming, don’t forget that they all are combinations of just two equations, Ohm’s law $\left(V=IR\right)$ and power $\left(P=IV\right)$ .

## Summary

• Electric power is the rate at which electric energy is supplied to a circuit or consumed by a load.
• Power dissipated by a resistor depends on the square of the current through the resistor and is equal to $P={I}^{2}R=\frac{{V}^{2}}{R}$ .
• The SI unit for electric power is the watt and the SI unit for electric energy is the joule. Another common unit for electric energy, used by power companies, is the kilowatt-hour (kW $·$ h).
• The total energy used over a time interval can be found by $E=\int Pdt$ .

## Conceptual questions

Common household appliances are rated at 110 V, but power companies deliver voltage in the kilovolt range and then step the voltage down using transformers to 110 V to be used in homes. You will learn in later chapters that transformers consist of many turns of wire, which warm up as current flows through them, wasting some of the energy that is given off as heat. This sounds inefficient. Why do the power companies transport electric power using this method?

Although the conductors have a low resistance, the lines from the power company can be kilometers long. Using a high voltage reduces the current that is required to supply the power demand and that reduces line losses.

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Please canu get more questions on electric field and electric flux please
Gbemisola
is electric field directly proportional to the squared of a distance
No electric field is inversely proportional to the squared distance between the charges
Gbemisola
The bullet 2.00cm long is fired at 420/s and passes straight through a 10.0 cm thick board existing at 280 m/s.What is the average acceleration of the bullet through the board?
FAUSTINA
an unstretched spring is 12cm long .A load of 5N stretched it to 15cm .how long will it be under a load of 15N?
Morapeli
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Compare the electric flux through the surface of a cube of side length a that has a charge q at its center to the flux through a spherical surface of radius a with a charge q at its center.
please I want to know how to solve increase in length
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what is the dimension symbol of temperature?
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Enthalpy is the degree ofdisorderlinessof a substance
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Sangeetha
s, p, d, f in this table
Sangeetha
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Vengata
Periodic table
Gbemisola
what are waves
In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities
Discuss how would orient a planar surface of area A in a uniform electric field of magnitude E0 to obtain (a) the maximum flux and (b) the minimum flux through the area.
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Find the net capacitance of the combination of series and parallel capacitors shown belo
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