# Effects of Resistance & Speed on Coil Pendulum Motion in Magnetic Field

• Flame666
In summary, the speed and resistance of a coil in pendulum motion in a magnetic field can affect the induced voltage and the decay of potential difference. Adding resistors to the circuit decreases the induced voltage, but as the resistance is lowered, a constant current mode of operation is eventually attained. Adding a 3.3ohm resistor to the circuit causes a drop in voltage, and the initial speed of the coil depends on the presence of a magnetic field. This behavior is consistent with the laws of physics and can be observed in the experiment described.
Flame666
How do resistance and speed of a coil in pendulum motion in a magnetic filed affect the induced voltage and the decay of Potential Difference?

Details:

Q1 When the speed of a coil is kept constant and a 3.3ohm resistor is added to the circuit of which the coil is a part of, the induced voltage drops. Why is this so? When the resistor is replaced with a 5.0ohm resistor the induced voltage for some reason increases and when the 5.0ohm resistor is replaced with a 6.8ohm resistor the induced voltage further increases. Why is this so? The induced voltage is considerably low when resistors are added to when compared to what the induced voltage is when a resistor is not added to the circuit.

Q2 why and how is the rate of decay of potential difference affected by resistance? The rate of decay of potential difference is highest when no resistor is added to the circuit followed by when a 6.8ohm resistor is added and then by a 5.0ohm and 3.3ohm resistor.

Note According to the data collected the induced current remains the same even when the resistance is changed.

I included the diagram of the setup. This is not a homework question.

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Refer to the above thread recently active. My comments in that thread cover what you're observing. Let me know if you need further detail. The induction issue was discussed at length. The induced voltage and current change as the resistance varies, to a point. As the resistance is lowered, a "constant current" mode of operation is eventually attained. Reducing the resistance further will not increase the current as it approaches a max limit.

If the resistance is increased indefinitely, the induced voltage will increase until it reaches a max limit. This becomes "constant voltage" behavior.

The key to understanding all going on here is CEL (conservation of energy law), AL (Amperes law). FL (Faradays law), OL (Ohms law). and LL (Lenz law). All 5 laws must be simultaneously upheld under all loading conditions.

What is happening in your experiment is perfectly consistent with the laws of physics. It can't be any other way. You just empirically proved what I covered in the above ref post. You got it right.

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Thanks for helping out but i still don't get why there is a drop in voltage when a 3.3ohm resistor is added to the circuit. In the original post i mentioned that the speed is kept constant and this done by displacing the pendulum bob by a certain distance, but this is not so. The speed is constant when there is no magnetic field, but when there is a magnetic field it changes depending on the resistance. the initial speed increases as resistance increases but is below the initial speed when there is no magnetic field. Although at higher resistance the speed decreases at a faster rate. can you explain why this is so.

Your diagram is not very detailed, so I can't give a detailed answer. I need to know how the magnetic field is generated, its direction, etc. Also, the orientation of the coil wrt the mag field is important. A more detailed diagram would help.

As far as the drop in voltage when 3.3 ohms is "added" to the circuit, is this 3.3 ohm *across* the coil terminals? Before the resistor is added, is the coil open circuited? Under open circuit conditions, maximum voltage will appear at the coil terminals. As the loading resistors are added, the voltage will decrease. If the resistor values are large, let's say in the megohm range, the voltage hardly changes, but the current changes inversely with resistance.

But, if the resistance is lowered enough, the voltage drops substantially. Constant voltage operation no longer takes place. If the resistance is lowered down to a low enough value, ohms in your case, a constant current region of operation is observed.

The link to the post from last week should explain it in detail. BR.

Claude

## 1. What is a coil pendulum and how does it work in a magnetic field?

A coil pendulum is a simple device consisting of a coil of wire attached to a pivot point, allowing it to swing freely. When placed in a magnetic field, the coil experiences a force due to the interaction between the magnetic field and the electric current flowing through the wire. This force causes the pendulum to oscillate back and forth.

## 2. How does resistance affect the motion of the coil pendulum?

Resistance refers to the opposition of electric current flow in the wire. In a coil pendulum, resistance can affect the strength of the magnetic field and therefore the amount of force experienced by the coil. This can impact the amplitude and frequency of the pendulum's motion, resulting in changes to its overall behavior.

## 3. Does the speed of the coil pendulum affect its motion in a magnetic field?

Yes, the speed of the coil pendulum can also impact its motion in a magnetic field. As the pendulum swings faster, it can generate a stronger electric current, resulting in a stronger force from the magnetic field. This can cause changes in the pendulum's amplitude and frequency, as well as its overall trajectory.

## 4. How does the strength of the magnetic field affect the coil pendulum's motion?

The strength of the magnetic field can have a significant impact on the motion of the coil pendulum. A stronger magnetic field can result in a stronger force on the coil, causing changes in its amplitude, frequency, and trajectory. It can also influence the resistance in the wire, further affecting the pendulum's behavior.

## 5. What are the practical applications of studying the effects of resistance and speed on coil pendulum motion in a magnetic field?

Studying the effects of resistance and speed on coil pendulum motion in a magnetic field can have various practical applications. It can help in understanding the behavior of electric current in different conditions and can also aid in the design and optimization of electrical devices, such as motors and generators, that utilize magnetic fields. Additionally, this research can have implications in fields such as renewable energy, where understanding the motion of electrical components is crucial.

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