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Four electrons are located at the corners of a square 10.0 nm on a side, with an alpha particle at its midpoint. Part A How much work is needed to move the alpha particle to the midpoint of one of the sides of the square?

Respuesta :

Answer:

Explanation:

The work done on alpha is given by

Charge on alpha particle is 2 the electron charge

[tex]W=\Delta U=U_{b}-U_{a} \quad \Rightarrow(1)[/tex]

The potential at center [tex]\left[U_{a}\right][/tex]

The electric potential due to multiples point charges is given by

[tex]U_{a}=k q q_{a} \sum_{i=1}^{4}\left(\frac{1}{r_{i}}\right) \quad \Rightarrow(2)[/tex]

where [tex]q[/tex]=charge on electron

[tex]q_{\alpha }[/tex]=charge on alpha particle

But  and is equal for all charges so ( 2) is equal to

[tex]U_{a}=\frac{4 k(-e)(2 e)}{d} \quad \Rightarrow(3)[/tex]

The radius  is given by

[tex]d=\frac{1}{2} \sqrt{(10)^{2}+(10)^{2}}=7.071 \mathrm{nC}[/tex]

Substitution in (3) yields

[tex]U_{a}=\frac{-8 \times 9 \times 10^{9} \times\left(1.6 \times 10^{-19}\right)^{2}}{7.071 \times 10^{-9}}=-2.607 \times 10^{-19} \mathrm{J}[/tex]

The potential at mid point [tex]\left[U_{b}\right][/tex]

due to lower charges the radius  is given by

[tex]r_{t}=\sqrt{L^{2}+(L / 2)^{2}}=\sqrt{10^{2}+5^{2}}=11.18 \mathrm{nm}[/tex]

And for upper charges the radius is

[tex]r_{u}=5 \mathrm{nm}[/tex]

So the electric potential is

[tex]U_{b} &=k q q_{a}\left[\frac{2}{r_{l}}+\frac{2}{r_{u}}\right][/tex]

[tex]=k(-e)(2 e)\left[\frac{2}{r_{1}}+\frac{2}{r_{u}}\right][/tex]

[tex]=-4 \times\left(1.6 \times 10^{9}\right)\left(1.6 \times 10^{-19}\right)^{2}\left[\frac{1}{11.18 \times 10^{-9}}+\frac{1}{5.0 \times 10^{-9}}\right][/tex]

[tex]=-2.667 \times 10^{-19} \mathrm{J}[/tex]

The work done on the charge is equal to

[tex]W=U_{b}-U_{a}=-2.667 \times 10^{-19}+2.607 \times 10^{-19}=-6.00 \times 10^{-21} \mathrm{J}[/tex]

The work done on  is given by

[tex]W=\Delta U=U_{b}-U_{a} \quad \Rightarrow(1)[/tex]

The potential at center [tex]\left[U_{a}\right][/tex]

The electric potential due to multiples point charges is given by

[tex]U_{a}=k q q_{a} \sum_{i=1}^{4}\left(\frac{1}{r_{i}}\right) \quad \Rightarrow(2)[/tex]

But  and is equal for all charges so ( 2) is equal to

[tex]U_{a}=\frac{4 k(-e)(2 e)}{d} \quad \Rightarrow(3)[/tex]

The radius  is given by

[tex]d=\frac{1}{2} \sqrt{(10)^{2}+(10)^{2}}=7.071 \mathrm{nC}[/tex]

Substitution in (3) yields

[tex]U_{a}=\frac{-8 \times 9 \times 10^{9} \times\left(1.6 \times 10^{-19}\right)^{2}}{7.071 \times 10^{-9}}=-2.607 \times 10^{-19} \mathrm{J}[/tex]

The potential at mid point [tex]\left[U_{b}\right][/tex]

due to lower charges the radius  is given by

[tex]r_{t}=\sqrt{L^{2}+(L / 2)^{2}}=\sqrt{10^{2}+5^{2}}=11.18 \mathrm{nm}[/tex]

And for upper charges the radius is

[tex]r_{u}=5 \mathrm{nm}[/tex]

So the electric potential is

[tex]U_{b} &=k q q_{a}\left[\frac{2}{r_{l}}+\frac{2}{r_{u}}\right][/tex]

[tex]=k(-e)(2 e)\left[\frac{2}{r_{1}}+\frac{2}{r_{u}}\right][/tex]

[tex]=-4 \times\left(1.6 \times 10^{9}\right)\left(1.6 \times 10^{-19}\right)^{2}\left[\frac{1}{11.18 \times 10^{-9}}+\frac{1}{5.0 \times 10^{-9}}\right][/tex]

[tex]=-2.667 \times 10^{-19} \mathrm{J}[/tex]

The work done on the charge is equal to

[tex]W=U_{b}-U_{a}=-2.667 \times 10^{-19}+2.607 \times 10^{-19}=-6.00 \times 10^{-21} \mathrm{J}[/tex]

[tex]W=-6.00 \times 10^{-21} \mathrm{J}[/tex]

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