Why do lights dim when a large appliance is switched on? The answer is that the

Question

Why do lights dim when a large appliance is switched on? The answer is that the large current the appliance motor draws causes a significant potential drop in the wires and reduces the voltage across the lights. This is called an IR drop because it is simply due to the current and resistance of the device in question. (a) Assume the bulb in question dissipates P_2 = 75 W when connected to the 120 V AC source. What average power will the bulb dissipate if I_1 = 16.5 A passes through the wires when the motor comes on? Assume a negligible change in bulb resistance, while the resistance of the wires are = 0.65 & Ohms;. P'_2 = (b) How many watts are consumed on average by the motor?

Explanation / Answer

part a:

resistance of bulb=voltage^2/power

=120^2/75=192 ohms

voltage drop across the wire=I1*R1=16.5*0.65=10.725 volts

then voltage across the bulb and the motor=120-10.725=109.28 volts

power consumed by the bulb=109.28^2/192=62.193 W

part b:

current through the bulb=voltage/resistance

=109.28/192=0.56917 A

current through the motor=16.5-0.56917=15.931 A

power consumed in motor=voltage*current

=109.28*15.931=1741 W

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.