The switch in the circuit shown in the figure below is closed, and the lightbulb glows steadily. The inductor is a simple air-core solenoid. An iron rod is inserted into the interior of the solenoid, increasing the magnitude of the magnetic field in the solenoid. As the rod is inserted, the brightness of the lightbulb
A) Increases
B)Decreases
C)Stays the same
I know its decreased, by why?
This is my thought process, decrease because the current will decrease in order to counteract the increase in magnetic field.
A current will be induced to resist the change in the magnetic field. That current will try to reduce the magnetic field within the solenoid. Use the right hand rule to figure out which way the current will be induced. If it aligns with the source, the bulb becomes brighter. If it opposes the source, the bulb will become dimmer.
Your thought process is on the right track! Let's break down the explanation step by step to clarify why the brightness of the lightbulb decreases when the iron rod is inserted.
1. When the switch is closed and the circuit is completed, a current flows through the solenoid, creating a magnetic field around it.
2. The iron rod, being a ferromagnetic material, has high magnetic permeability compared to air. When the rod is inserted into the solenoid, it increases the magnitude of the magnetic field within the solenoid.
3. According to Lenz's Law, when there is a change in the magnetic field through a closed loop, an electromotive force (EMF) is induced in the loop that opposes the change. In this case, since the magnetic field is increasing, the induced EMF will act to oppose the increased magnetic field.
4. The induced EMF creates a current in the circuit that flows in the opposite direction to the original current, trying to reduce the magnetic field within the solenoid.
5. Using the right-hand rule, if you align your fingers with the induced current and curl them in the direction of the original current, your thumb will point opposite to the direction of the increased magnetic field.
6. This means that the induced current flows in the opposite direction to the original current, reducing the overall current in the circuit.
7. The brightness of the lightbulb is directly proportional to the current flowing through it. Therefore, as the overall current decreases due to the induced current opposing the increased magnetic field, the brightness of the lightbulb decreases.
So, the correct answer is B) Decreases.