Electric Fields: Charge/Unit Length on Inner Surface of Coaxial Cable

In summary, the conversation discusses the concept of charge per unit length on the inner surface of a hollow cylindrical metal tube placed around a wire with infinite charge. The speaker suggests using Gauss's law to calculate the charge and questions if there are any differences between this scenario and using a gaussian surface. The other person explains that, due to the polar accumulation of charges, the inner surface of the cylinder will have a charge density and clarifies that the charge per unit length is not 0. They also express their enjoyment of physics and thank the other person for their help.
  • #1
steph124355
4
0
I'm a little stuck on the theory behind this question:

(in relation to a line of infinite charge: a wire)
A hollow cylindrical metal tube with inner radius 2.5mm is now placed around the wire, to form a coaxil cable. What will be the charge per unit length on the inner surface of the tube. Explain.

I am thinking it is 0, how or why i got that I don't know!
 
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  • #2
Hint: Make use of Gauss's law.
 
  • #3
Use Gauss' law as though the cylinder is not there?
In which case to calculate using E= λ/(2πε_0 r) and use the 2.5mm as the radial distance?

Is there any different concepts behind this scenario compared to using a gaussian surface?
 
  • #4
steph124355 said:
(in relation to a line of infinite charge: a wire)

Infinite charge...wow...wonder how that happens
 
  • #5
Its not 0. Considering that metals are good conductors, what happens is that when placed in an electric field, a polar accumulation of charges occur (meaning the positive charges go in one direction and the negative in the other). Therefore, charges accumulate on the surfaces of the cylinder. The inner surface will have a charge density.
 
  • #6
haha thanks!
physics does my head in but i enjoy it!
thanks for your help
 

Related to Electric Fields: Charge/Unit Length on Inner Surface of Coaxial Cable

1. What is an electric field?

An electric field is a physical quantity that describes the influence that a charged object has on other charged objects in its surroundings. It is represented by a vector and is measured in units of newtons per coulomb (N/C).

2. How is the electric field calculated for a coaxial cable?

The electric field for a coaxial cable can be calculated using the formula E = (λ/2πε0r)2, where λ is the charge per unit length on the inner surface of the cable, ε0 is the permittivity of free space, and r is the distance from the center of the cable to the point where the electric field is being measured.

3. What is the significance of the charge per unit length on the inner surface of a coaxial cable?

The charge per unit length on the inner surface of a coaxial cable determines the strength of the electric field within the cable. It is directly proportional to the electric field, so a higher charge per unit length will result in a stronger electric field.

4. How does the electric field change as you move from the inner surface to the outer surface of a coaxial cable?

The electric field within a coaxial cable decreases as you move from the inner surface to the outer surface. This is because the charge on the inner surface is spread out over a larger area on the outer surface, resulting in a weaker electric field.

5. Can the charge per unit length on the inner surface of a coaxial cable be negative?

Yes, the charge per unit length on the inner surface of a coaxial cable can be negative. This would result in an electric field in the opposite direction compared to a positive charge per unit length. However, in practice, coaxial cables are designed to have a positive charge per unit length on the inner surface to ensure proper function.

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