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| ### Statement |
| ### Statement |
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| \\\\\\\$6.2.10.\\\\\\\$ Two infinite planes intersecting at an angle \\\\\\\$\\\\\\\\alpha\\\\\\\$ divide space into four regions. What is the electric field strength in regions 1 and 2 if the surface charge density of the planes is \\\\\\\$\\\\\\\\pm \\\\\\\\sigma\\\\\\\$? |
| $6.2.10.$ Two infinite planes intersecting at an angle $\alpha$ divide space into four regions. What is the electric field strength in regions 1 and 2 if the surface charge density of the planes is $\pm \sigma$? |
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| ### Solution |
| ### Solution |
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| Consider the following figure... |
| Consider the following figure... |
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| It's known that the electric field intensity for one of the faces of a infinite plane with surface charge density is \\\\\\\$E = \\\\\\\\frac{\\\\\\\\sigma}{2\\\\\\\\varepsilon_0}\\\\\\\$. |
| It's known that the electric field intensity for one of the faces of a infinite plane with surface charge density is $E = \frac{\sigma}{2\varepsilon_0}$. |
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| For region 1 (see part \\\\\\\$a\\\\\\\$ of above figure): |
| For region 1 (see part $a$ of above figure): |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R1y} = E - E \\\\\\\\cos{\\\\\\\\alpha} = \\\\\\\\frac{\\\\\\\\sigma}{2\\\\\\\\varepsilon_0}(1-\\\\\\\\cos{\\\\\\\\alpha}) |
| E_{R1y} = E - E \cos{\alpha} = \frac{\sigma}{2\varepsilon_0}(1-\cos{\alpha}) |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| and for \\\\\\\$x\\\\\\\$-direction, |
| and for $x$-direction, |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R1x} = E \\\\\\\\sin{\\\\\\\\alpha} = \\\\\\\\frac{\\\\\\\\sigma}{2\\\\\\\\varepsilon_0}\\\\\\\\sin{\\\\\\\\alpha}. |
| E_{R1x} = E \sin{\alpha} = \frac{\sigma}{2\varepsilon_0}\sin{\alpha}. |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| So, as |
| So, as |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R1} = \\\\\\\\sqrt{E_{R1x}^2+E_{R1y}^2}, |
| E_{R1} = \sqrt{E_{R1x}^2+E_{R1y}^2}, |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| and taking in account that |
| and taking in account that |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| \\\\\\\\sin{\\\\\\\\alpha} = \\\\\\\\sqrt{\\\\\\\\frac{1-\\\\\\\\cos{\\\\\\\\alpha}}{2}}, |
| \sin{\frac{\alpha}{2}} = \sqrt{\frac{1-\cos{\alpha}}{2}}, |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| it is obtained |
| it is obtained |
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| #### Answer 1 |
| #### Answer 1 |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R1} = \\\\\\\\frac{\\\\\\\\sigma}{\\\\\\\\varepsilon_0}\\\\\\\\sin{\\\\\\\\frac{\\\\\\\\alpha}{2}} |
| E_{R1} = \frac{\sigma}{\varepsilon_0}\sin{\frac{\alpha}{2}} |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| For region 2, for \\\\\\\$y\\\\\\\$-direction: |
| For region 2, for $y$-direction: |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R2y} = E(1+\\\\\\\\cos{\\\\\\\\alpha})=\\\\\\\\frac{\\\\\\\\sigma}{2\\\\\\\\varepsilon_0}(1+\\\\\\\\cos{\\\\\\\\alpha}) |
| E_{R2y} = E(1+\cos{\alpha})=\frac{\sigma}{2\varepsilon_0}(1+\cos{\alpha}) |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| and for \\\\\\\$x\\\\\\\$-axis, |
| and for $x$-axis, |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R2x} = E\\\\\\\\sin{\\\\\\\\alpha} = \\\\\\\\frac{\\\\\\\\sigma}{2\\\\\\\\varepsilon_0}\\\\\\\\sin{\\\\\\\\alpha}. |
| E_{R2x} = E\sin{\alpha} = \frac{\sigma}{2\varepsilon_0}\sin{\alpha}. |
| \\\\\\\$\\\\\\\$ |
| $$ |
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| Again, |
| Again, |
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| \\\\\\\$\\\\\\\$ |
| $$ |
| E_{R2} = \\\\\\\\sqrt{E_{R2x}^2+E_{R2y}^2} |
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| \\\\\\\$\\\\\\\$ |
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| and taking in account that |
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| \\\\\\\$\\\\\\\$ |
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| \\\\\\\\cos{\\\\\\\\frac{\\\\\\\\alpha}{2}} = \\\\\\\\sqrt{\\\\\\\\frac{1+\\\\\\\\cos{\\\\\\\\alpha}}{2}} |
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| \\\\\\\$\\\\\\\$ |
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| #### Answer 2 |
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| \\\\\\\$\\\\\\\$ |
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| E_{R2} = \\\\\\\\frac{\\\\\\\\sigma}{\\\\\\\\varepsilon_0}\\\\\\\\cos{\\\\\\\\frac{\\\\\\\\alpha}{2}} |
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| \\\\\\\$\\\\\\\$ |
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