Posted by **ashley** on Tuesday, October 11, 2011 at 1:54pm.

A 75.0-W lamp is placed in series with a resistor and a 120.0-V source. If the voltage across the lamp is 24 V, what is the resistance R of the resistor?

- physics -
**drwls**, Tuesday, October 11, 2011 at 3:09pm
The voltage drop across the resistor is 120 - 24 = 96 V

The resistance R' of the lamp can be derived from its Wattage at 120 V:

75 W = V^2/R' = 14400/R'

R' = 192 ohms

Since the lamp gets 24/120 = 20% of the voltage drop, the other 80% of the voltage (96 V) is across the resistor.

With both in series, circuit current = lamp current = 24 V/192 ohms = 0.125 Amps

Resistor resistance = V(resistor)/I

= 96/(1/8) = 768 ohms

- physics -
**Henry**, Monday, May 4, 2015 at 10:13pm
Vr = 120-24 = 96 V. = Voltage across the

resistor.

V*I = 75W.

24I = 75

I = 3.125A = Lamp current

R = Vr/I = 96/3.125 = 30.72 Ohms in series with lamp.

## Answer This Question

## Related Questions

- Physics - A 22-ohm resistor and a 33-ohm resistor are connected in series and ...
- Physics - A 100 W lamp is connected to 120 V, and its current is measured. A ...
- physics - A 37 ohm lamp and a 59 ohm lamp are connected in series and placed ...
- College Physics - A simple circuit is made of a power source, a rheostat and an ...
- Physics - A 37 ohm lamp and a 59 ohm lamp are connected in series and placed ...
- Physics - Could some one tell m if this is right? 1)Does currend flow through a ...
- physics - A 15-V battery is hooked up to three resistors in series. The voltage ...
- Physics - 1)If a resistor is added to a parallel circuit, the equivalent ...
- Physics 2 - A(n) 78-Ù resistor and a 68-Ù resistor are connected in series ...
- physics. - resistors of 30 ohms and 60 ohms are connected in parallel and joined...

More Related Questions