# Niels Bohr atom and magnetic fiels

• tiagobt
In summary, according to Bohr's model, an electron orbits a proton at a distance of 5.29 \times 10^{-11} m with a velocity of 2.19 \times 10^6 m/s. The intensity of the magnetic field produced by this movement is given by the Biot-Savart Law, which states that the field intensity is proportional to the charge of the electron multiplied by the area of the current conductor.
tiagobt
Niels Bohr atom and magnetic fields

Could anyone help me solve the following problem?

According to 1913 Niels Bohr hydrogen atom model, an electron orbits a proton from a distance of $5.29 \times 10^{-11} m$ with a velocity of $2.19 \times 10^6 m/s$. Find the intensity of the magnetic field produced by this movement in the position of the proton.
I am supposed to use Biot-Savart Law. What I tried was:

The orbit of the electron can be interpreted as a current flowing in a circular spire (on the opposite direction of the electron's velocity). If an element $d \vec{s}$ of the spire produces a field $d \vec{B}$ in the position of the proton, the intensity of $d \vec{B}$ can be written as the following:

$dB = \frac{\mu_0ids}{4 \pi R^2}$

$B = \frac{\mu_0i}{4 \pi R^2} \oint ds$

Calculating the integral for the entire circle:

$B = \frac{\mu_0i2 \pi R}{4 \pi R^2} = \frac{\mu_0i}{2R}$

And then I tried to calculate the electical current as a function of the electron's velocity of displacement:

$i = nq_{e}v_{d}A$

Where $n$ is the number of free charged particles, $q_e$ is the charge of an electron, $v_d$ is the velocity of displacement of the charge and $A$ is the area of section of the current conductor. I am not sure what $A$ could be in the original problem. Am I making any sense?

Thanks,

Tiago

Last edited:
tiagobt said:
And then I tried to calculate the electical current as a function of the electron's velocity of displacement:

$i = nq_{e}v_{d}A$

That's the formula for the current in a conductor of cross-section A, in terms of the motion of the electrons in it. In the Bohr atom, you don't have a conductor, you don't have a cross-section, and you don't have a number density of electrons (n).

What you do have is a single electron traveling in a circular path. Suppose you're standing next to a point on that circular path (and that you're very tiny ). How many times per second does that electron pass you? How many coulombs per second does that work out to, counting each "pass" as a separate chunk of charge?

Thanks so much! I think I got it now. Just to make sure my ideas are correct:

In each period $T$, the electron passes through the point "where I am standing" once. That means that there is a charge of $q_e$ every $T$ seconds:

$i = \frac{q_e}{T} = \frac{q_e}{\frac{2 \pi R}{v}} = \frac{q_e v}{2 \pi R}$

Sustituting $i$ in Biot-Savart Law:

$B = \frac{\mu_0}{2R} \frac{q_e v}{2 \pi R} = \frac{\mu_0 q_e v}{4 \pi R^2} = k_m \frac{q_e v}{R^2}$

I think that's it!

Thanks again

Last edited:
Yep, that's it. You even did it algebraically, without plugging in any numbers until the end! :!) My students always calculate every intermediate number along the way unless I whack them by taking points off for it.

Having done a classical calculation of the field at the proton, it is just one step further to calculate the interaction energy of the proton spin with this field. That, at least might tell you something. I don't see what physical idea comes out of calculating the field alone...perhaps it's just to give you practice with calculations like this?

## 1. What is the Niels Bohr atom model?

The Niels Bohr atom model is a representation of an atom proposed by Danish physicist Niels Bohr in 1913. It is based on the idea that electrons orbit the nucleus in specific energy levels, rather than freely moving around the nucleus.

## 2. How does the Niels Bohr atom model explain the stability of atoms?

The Niels Bohr atom model explains the stability of atoms by stating that electrons can only occupy specific energy levels, and they cannot exist in between these levels. This means that electrons are not constantly losing energy and collapsing into the nucleus, which would make the atom unstable.

## 3. What is the significance of the magnetic field in the Niels Bohr atom model?

The magnetic field plays a crucial role in the Niels Bohr atom model as it helps to explain the behavior of electrons in atoms. According to the model, electrons have spin, which creates a magnetic moment. This magnetic moment interacts with the external magnetic field, causing the electrons to move in a circular orbit around the nucleus.

## 4. How does the Niels Bohr atom model explain the spectral lines of elements?

The Niels Bohr atom model explains the spectral lines of elements by stating that when electrons move from one energy level to another, they emit or absorb energy in the form of light. Each possible energy transition has a specific wavelength of light associated with it, resulting in a unique spectral line for each element.

## 5. What are the limitations of the Niels Bohr atom model?

The Niels Bohr atom model has several limitations, such as not being able to explain the spectra of more complex atoms, such as those with multiple electrons. It also does not account for the wave-like nature of electrons, which is a fundamental aspect of quantum mechanics. However, the model was a significant contribution to our understanding of atomic structure and laid the foundation for further advancements in quantum theory.

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