Recharging a battery when Lightbulb and TV are in parallel

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Homework Help Overview

The problem involves calculating the time required for a wind generator to recharge a battery while powering a light bulb and a TV connected in parallel. The light bulb has a resistance of 100Ω and operates on a 100 V line, while the TV consumes 100 W of power. The scenario is set in a household context where both devices are used for a duration of 200 minutes.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the power consumed by the light bulb and TV, questioning the resistance values and the overall energy requirements. There is an exploration of the relationship between power consumption and generation, with suggestions to write out power equations for clarity.

Discussion Status

Some participants have provided guidance on considering the power equations for the TV, light bulb, and wind generator. There is acknowledgment of different scenarios regarding when the wind power is available relative to the operation of the appliances. A calculation attempt has been made, leading to a proposed time for recharging the battery.

Contextual Notes

Participants note the need for clarity on the wind power equation and the implications of energy conservation principles. There is mention of non-standard units being used in the calculations, which may affect the interpretation of results.

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Homework Statement


In a household, the wife reads a book that uses a light bulb that has a resistance of 100Ω and is connected to a 100 V line while the husband watches a TV that draws 100 W of power. They do these actives for 200 mins. Power comes from a wind generator that charges batteries. The wind supplies 10 amperes at a voltage of 100 V.

How long must the wind blow to recharge the battery.

Homework Equations


V=IR
P= V2/r

The Attempt at a Solution


Modeled the circuit to have the light bulb and tv in parrallel. Using the power equation, the tv also has 100Ω of resistance which doesn't make to much sense to me.

Power is J/s so we know that 200 min is 12000s which tell us 1.2 MJ is required to charge the battery.
 
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Think about W consumed and W generated, that may make it clearer for you. You don't need a circuit diagram to solve this. You are missing an equation for wind power - what is it? That is key to seeing the solution in the simplest way. Write three power equations -

TV Power =
Light Power =
Wind Power =

That should help.

I see two potential answers - one (trivial) answer assuming the wind is blowing while the appliances are drawing power, and a different answer assuming the wind only starts blowing after the appliances have been turned off.
 
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Grinkle said:
Think about W consumed and W generated, that may make it clearer for you. You don't need a circuit diagram to solve this. You are missing an equation for wind power - what is it? That is key to seeing the solution in the simplest way. Write three power equations -

TV Power =
Light Power =
Wind Power =

That should help.

I see two potential answers - one (trivial) answer assuming the wind is blowing while the appliances are drawing power, and a different answer assuming the wind only starts blowing after the appliances have been turned off.

Thank you for the response.

The missing equation is P=IV which helps us calculate the Wind Power

I've calculated the following:
TV Power = 100W
Light Power = 100W
Wind Power = 1000W

Since a watt is a J/s then the TV and Light require 2.4x106 J
Divide power required by wind power and we get 2400 s which is 40 minutes? Does that sound correct?
 
40 mins is correct.

You can also get to same answer using
Energy out = Energy In
200W * 200mins = 1000W * 40mins

Ok so the Watt.min isn't an SI unit but that doesn't matter.
 
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