- #1
brad sue
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HI I don't understand the method of image.
I have this problem:
A uniform charged disk is suspended ( at a distance h) above an infinite conducting plane ( disk is parallel to the plane). The disk carries a charge Q and has a diameter d. Assume d>>h.
1- Calculate the electric field vector near the center and below the disk.
2- Calculate the capacitance of the system using the formula C=Q/V.
3- Calculate the capacitance of the system using the energy formulas.
I attach a picture.
I get lost at some point
the electric fiel for a disk is:
E=Qy/(2*pi*epsilon)*(1/y-1/(sqrt(y^2+R^2)) y (unit vector)
to answer the question 1-:
electric field from charge Q:
EQ=Q(h-y)/(2*pi*epsilon)*(1/(h-y)-1/(sqrt((h-y)^2+R^2)) (-y) (unit vector)
electric field from charge -Q ( the image):
E-Q=-Q(h+y)/(2*pi*epsilon)*(1/(h+y)-1/(sqrt((h+y)^2+R^2)) (-y) (unit vector)
Here is my first problem: the direction of the two electric fields EQ and E-Q.
I am not sure about the electric field of the expressions.
(I suspect I get some mistakes because I tried a similar problem but with a more simple expression for the 2 fields and when I add them, I get zero)
I would really have some help with this problem.
please can someone help me?
Thank you
I have this problem:
A uniform charged disk is suspended ( at a distance h) above an infinite conducting plane ( disk is parallel to the plane). The disk carries a charge Q and has a diameter d. Assume d>>h.
1- Calculate the electric field vector near the center and below the disk.
2- Calculate the capacitance of the system using the formula C=Q/V.
3- Calculate the capacitance of the system using the energy formulas.
I attach a picture.
I get lost at some point
the electric fiel for a disk is:
E=Qy/(2*pi*epsilon)*(1/y-1/(sqrt(y^2+R^2)) y (unit vector)
to answer the question 1-:
electric field from charge Q:
EQ=Q(h-y)/(2*pi*epsilon)*(1/(h-y)-1/(sqrt((h-y)^2+R^2)) (-y) (unit vector)
electric field from charge -Q ( the image):
E-Q=-Q(h+y)/(2*pi*epsilon)*(1/(h+y)-1/(sqrt((h+y)^2+R^2)) (-y) (unit vector)
Here is my first problem: the direction of the two electric fields EQ and E-Q.
I am not sure about the electric field of the expressions.
(I suspect I get some mistakes because I tried a similar problem but with a more simple expression for the 2 fields and when I add them, I get zero)
I would really have some help with this problem.
please can someone help me?
Thank you