# Magnetic field and generator power output

• B
• dansmith170
In summary, the conversation discusses the relationship between magnetic field, frequency, and power output in a generator. The equations used show that frequency is inversely proportional to magnetic field, and decreasing the magnetic field could potentially increase the frequency and therefore the power output of the generator. However, it is important to consider other factors such as maintaining a constant torque and the source of the current.
dansmith170
TL;DR Summary
Could decreasing the magnetic field increase a generator's power output?
Hi,

I am confused about whether decreasing the magnetic field used for a generator could increase the generator's power output.

I used four equations:

1. Torque = Force x radius
2. Torque = NIAB (N = number of turns, I = current, A = area of armature, B = magnetic field).
3. emf = NAB(2*pi*f) (emf = electromotive force, f = frequency of rotation of armature.
4. I = emf / R (R = resistance)

Using these equations, I found that frequency is inversely proportional to magnetic field ("f" is proportional to "1/B^2"). If that is the case, then decreasing magnetic field should actually increase frequency, correct?

A generator should produce more power when the frequency is greater. Well then, a generator with lower magnetic field, provided that it has greater frequency, should produce more power.

I get the feeling that I made a mistake somewhere in my math or reasoning, would someone please help me out on this?

Thanks.

Citations to sources for relevant equations:
https://courses.lumenlearning.com/suny-physics/chapter/23-5-electric-generators/
http://spiff.rit.edu/classes/phys213/lectures/amp/amp_long.html

To keep a constant emf, if the B field is lower, the frequency has to be increased. The frequency compensates for a low B field in order to maintain an emf. The power is not greater.

osilmag said:
To keep a constant emf, if the B field is lower, the frequency has to be increased. The frequency compensates for a low B field in order to maintain an emf. The power is not greater.
osilmag, thanks for your response. Suppose I do not want to keep a constant emf, but I do want to keep a constant torque. In that case, would lowering the B field mean increasing frequency (f) in a way that increases total power output of the generator?

If you wanted a constant torque when your B field lowered, your current would have to increase. That has to come from your current source. Is the current in equation 2 the same as in equation 4?

Last edited:
osilmag said:
If you wanted a constant torque when your B field lowered, your current would have to increase. That has to come from your current source. Is the current in equation 2 the same as in equation 4?
Yeah, same current (I) in both equations.

The current source is, I think, from the mechanical force that is spinning the generator's armature (maybe it is a wind-powered generator). In that case, the generator's armature spin, measured in frequency (f) should determine the current (I) magnitude.

In other words, given that current (I) is proportional to (B) times (f) (see equations 3 and 4), if I decrease (B) but (I) increases, then (f) must increase by a greater amount than (B) has decreased by.

Agree?

osilmag
Agree

## What is the relationship between magnetic field strength and generator power output?

The power output of a generator is directly related to the strength of the magnetic field. A stronger magnetic field increases the amount of induced electromotive force (EMF) in the generator's coils, which in turn increases the power output. This is because the EMF is proportional to the rate of change of the magnetic flux, which is enhanced by a stronger magnetic field.

## How does the speed of the generator's rotor affect the power output?

The speed of the generator's rotor is crucial for power output. Faster rotation speeds increase the rate at which the magnetic field lines are cut by the coils, leading to a higher induced EMF and thus greater power output. However, there are practical limits to how fast the rotor can spin due to mechanical and thermal constraints.

## Can a generator work without a magnetic field?

No, a generator cannot work without a magnetic field. The fundamental principle of electromagnetic induction, which generators rely on, requires a changing magnetic field to induce an EMF in the coils. Without a magnetic field, there would be no induced voltage and therefore no power output.

## What materials are typically used for the magnets in generators?

Generators commonly use either permanent magnets or electromagnets. Permanent magnets are typically made from materials like neodymium, iron, and boron (NdFeB), or samarium cobalt (SmCo). Electromagnets are made from coils of wire, usually copper, wound around a core of ferromagnetic material like iron to enhance the magnetic field strength when current flows through the coils.

## How does the load on a generator affect its magnetic field and power output?

The load on a generator affects its power output but not the magnetic field directly. As the load increases, the generator must produce more current to meet the demand, which can cause a voltage drop if the generator is not designed to handle the increased load efficiently. This can lead to a decrease in power output if the generator's capacity is exceeded. However, the magnetic field strength itself is typically maintained by the generator's design and operation parameters.

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