What resistance is needed if current is .300 A?

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SUMMARY

The discussion centers on calculating the resistance needed to reduce the current to 0.300 A for a 75.0 W bulb connected to a 120 V source. The initial calculation using the formula R = V/I yields 400 ohms, but the correct resistance required is 210 ohms. This discrepancy arises from not accounting for the resistance of the bulb itself, which must be included in the total resistance equation R_bulb + R_dimmer = V_total/I.

PREREQUISITES
  • Understanding of Ohm's Law (R = V/I)
  • Familiarity with power calculations (P = V^2/R)
  • Knowledge of series circuits and total resistance calculations
  • Basic electrical concepts such as voltage, current, and resistance
NEXT STEPS
  • Calculate the resistance of the bulb using P = V^2/R
  • Explore series circuit principles to understand total resistance
  • Learn about dimmer switches and their impact on circuit resistance
  • Investigate practical applications of resistance calculations in electrical engineering
USEFUL FOR

Students studying electrical engineering, electricians working with lighting systems, and anyone interested in understanding circuit resistance and current control.

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Homework Statement


A 75.0 W bulb is connected to a 120 V source. A lamp dimmer puts a resistance in series with the bulb. What resistance would be needed to reduce the current to .300 A?


Homework Equations


R=V/I


The Attempt at a Solution



R=120/.3A=400 ohms. The answer is 210 ohms. What am I missing?
 
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Here's another relevant equation.

[tex](R_{bulb} + R_{dimmer} = V_{total}/I[/tex]
 
Here is one more:

[tex]P=V^2/R[/tex]
 

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