What is the Ratio of Resistances in a Series Circuit with 20% Power Dissipation?

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AI Thread Summary
To determine the ratio of resistances R1 and R2 in a series circuit where 20% of the power is dissipated through R1, it is essential to apply the principles of power dissipation and Ohm's Law. The initial approach of dividing the power percentages (20% and 80%) to find a ratio of 0.25 is not mathematically sound. Instead, one should set up an equation using the power dissipation formula, which relates voltage, current, and resistance. By expressing power in terms of resistances and current, the variables can be simplified, allowing for a correct calculation of the ratio R1/R2. Ultimately, precise mathematical analysis is crucial for accurate results rather than relying solely on intuitive reasoning.
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Hey guys so I'm new here but really need help with just with a confirmation on the answer on this question.

Homework Statement



Two resistors R1 and R2 are connected in series and these are connected in series to a battery. If 20% of the power coming from the battery is dissipated through the R1 resistor, determine the ratio R1/R2.

Homework Equations



R=V/I (just moved around Ohms Law)

The Attempt at a Solution



Well since the resistor is in a series you normally would add them together. Since you lose 20% of the power through the first resistor you have 80% left. So I'm not positive but i figured you would just divide 20/80 and you end up with 0.25. Thanks for the help I appreciate it.
 
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Be careful with that reasoning. Power dissipation is VI = R I^2. Set up the equation for current in terms of R1 R2 and the voltage of the battery V. Write the ratio of powers expressed in terms of the resistances and the current and the value of V should cancel as should the currents. You'll get an expression for the ratio in terms of the Resistances R1 and R2. You can then solve that equation for R1 i.t.o. R2 or vice versa and work out their ratio. It may end up being as your intuition reasoned but you will be using fact and not intuition. (Or it may be completely different. Don't assume, Do The Math!)
 
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