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ian2012

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I've got a problem understanding a line of proof in my lecture notes.

Given that you have a charge of +Q and mass m orbiting a fixed particle of charge -Q' in the presence of a magnetic field

Given that:

[tex]m\hat{a_{I}}=-\frac{QQ'}{4\pi\epsilon_{0}r^{2}}\hat{r}+Q\hat{v_{I}} \times \hat{B}[/tex]

where [tex]\hat{v_{I}}[/tex] is the particle's velocity in the inertial frame.

Substituting

[tex]\hat{a_{I}}=\hat{a_{R}}+2\hat{\omega} \times \hat{v_{R}}+\hat{\omega} \times (\hat{\omega} \times \hat{r})[/tex]

into the first equation along with [tex]\hat{v_{I}}=\hat{v_{R}}+\hat{\omega} \times \hat{r}[/tex]

gives:

[tex]\hat{a_{R}}+2\hat{\omega} \times \hat{v_{R}}+\hat{\omega} \times (\hat{\omega} \times \hat{r})[/tex] = [tex]-\frac{QQ'}{4\pi\epsilon_{0}mr^{2}}\hat{r}+(\frac{Q}{m})[\hat{v_{R}}+(\hat{\omega} \times \hat{r})] \times \hat{B}[/tex]

Apparently the terms porportional to [tex]\hat{v_{R}}[/tex] cancel if [tex]\hat{\omega}=-\frac{Q}{2m}\hat{B}[/tex]

Why is this so? Visualizing the situation will probably help a lot.

Given that you have a charge of +Q and mass m orbiting a fixed particle of charge -Q' in the presence of a magnetic field

**B**. The particle is moving slowly enough for relativistic effects to be ignored.Given that:

[tex]m\hat{a_{I}}=-\frac{QQ'}{4\pi\epsilon_{0}r^{2}}\hat{r}+Q\hat{v_{I}} \times \hat{B}[/tex]

where [tex]\hat{v_{I}}[/tex] is the particle's velocity in the inertial frame.

Substituting

[tex]\hat{a_{I}}=\hat{a_{R}}+2\hat{\omega} \times \hat{v_{R}}+\hat{\omega} \times (\hat{\omega} \times \hat{r})[/tex]

into the first equation along with [tex]\hat{v_{I}}=\hat{v_{R}}+\hat{\omega} \times \hat{r}[/tex]

gives:

[tex]\hat{a_{R}}+2\hat{\omega} \times \hat{v_{R}}+\hat{\omega} \times (\hat{\omega} \times \hat{r})[/tex] = [tex]-\frac{QQ'}{4\pi\epsilon_{0}mr^{2}}\hat{r}+(\frac{Q}{m})[\hat{v_{R}}+(\hat{\omega} \times \hat{r})] \times \hat{B}[/tex]

Apparently the terms porportional to [tex]\hat{v_{R}}[/tex] cancel if [tex]\hat{\omega}=-\frac{Q}{2m}\hat{B}[/tex]

Why is this so? Visualizing the situation will probably help a lot.

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