You are working as a demonstration assistant for a physics professor. He shows you the circuit in the following figure, which he wants you to build for an upcoming class. R2 R1 The lightbulb is a household incandescent bulb that receives energy at the rate of 40.0 W when operating at 120 V. It has a resistance R,, which, for simplicity, we will assume is constant at all operating voltages. The battery in the circuit has an emf of 30.0 V. When the switch has been closed for a long time, the bulb glows dimly, since it is powered by only 30.0 v. When the switch is opened, however, the bulb flashes brightly and then gradually dims to darkness. Your professor wants you to determine two values. Assume a resistance-free inductor and that the resistance of the lightbulb does not vary with temperature. (a) Find the resistance R, (in Q) that is necessary for the bulb to initially flash, when the switch is opened, at the same brightness it would have if plugged into a 120 v socket. Ω (b) Find the inductance L (in kH) necessary to keep the current in the lightbulb above 50.0% of its value when the switch is opened, for a time interval of 6.50 s after it is opened. kH

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You are working as a demonstration assistant for a physics professor. He shows you the circuit in the following figure, which he wants you to build for an upcoming class.
R2
R1
The lightbulb is a household incandescent bulb that receives energy at the rate of 40.0 W when operating at 120 V. It has a resistance R,, which, for simplicity, we will assume
is constant at all operating voltages. The battery in the circuit has an emf of 30.0 V. When the switch has been closed for a long time, the bulb glows dimly, since it is powered
by only 30.0 v. When the switch is opened, however, the bulb flashes brightly and then gradually dims to darkness. Your professor wants you to determine two values. Assume
a resistance-free inductor and that the resistance of the lightbulb does not vary with temperature.
(a) Find the resistance R, (in Q) that is necessary for the bulb to initially flash, when the switch is opened, at the same brightness it would have if plugged into a 120 v
socket.
Ω
(b) Find the inductance L (in kH) necessary to keep the current in the lightbulb above 50.0% of its value when the switch is opened, for a time interval of 6.50 s after it is
opened.
kH
Transcribed Image Text:You are working as a demonstration assistant for a physics professor. He shows you the circuit in the following figure, which he wants you to build for an upcoming class. R2 R1 The lightbulb is a household incandescent bulb that receives energy at the rate of 40.0 W when operating at 120 V. It has a resistance R,, which, for simplicity, we will assume is constant at all operating voltages. The battery in the circuit has an emf of 30.0 V. When the switch has been closed for a long time, the bulb glows dimly, since it is powered by only 30.0 v. When the switch is opened, however, the bulb flashes brightly and then gradually dims to darkness. Your professor wants you to determine two values. Assume a resistance-free inductor and that the resistance of the lightbulb does not vary with temperature. (a) Find the resistance R, (in Q) that is necessary for the bulb to initially flash, when the switch is opened, at the same brightness it would have if plugged into a 120 v socket. Ω (b) Find the inductance L (in kH) necessary to keep the current in the lightbulb above 50.0% of its value when the switch is opened, for a time interval of 6.50 s after it is opened. kH
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