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PhysicsTest

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- Homework Statement
- To calculate the electric field from the charge density inside the BJT.

- Relevant Equations
- ##dE = \frac {dq} {4\pi\epsilon r^2}##

There is a section in the BJT explanation the charge density and the corresponding electric field graphs. But i was not sure how the electric field is derived and hence i started deriving it. Please correct me if my understanding is wrong in posting the question

It is an ##npn## BJT. My derivation is

##dE = \frac {dq} {4\pi\epsilon r^2}##

If i only calculate only for the 1st region

##dq = \rho dx##

I am assuming at some distance x1,

##dE = \int_0^{x1}\frac{\rho dx} {4\pi\epsilon x^2}##

##E = [\frac{\rho} {4\pi\epsilon x}]_0^{x1}##

I am really not sure if I am proceeding properly?

It is an ##npn## BJT. My derivation is

##dE = \frac {dq} {4\pi\epsilon r^2}##

If i only calculate only for the 1st region

##dq = \rho dx##

I am assuming at some distance x1,

##dE = \int_0^{x1}\frac{\rho dx} {4\pi\epsilon x^2}##

##E = [\frac{\rho} {4\pi\epsilon x}]_0^{x1}##

I am really not sure if I am proceeding properly?

Last edited: