<< Chapter < Page Chapter >> Page >

Inhomogeneous electric field

What is the total flux of the electric field E = c y 2 k ^ through the rectangular surface shown in [link] ?

A rectangle labeled S is shown in the xy plane. Its side along y axis is of length a and that along the x axis measures b. A strip is marked on the rectangle, with its length parallel to x axis. Its length is b and its breadth is dy. Its area is labeled dA equal to b dy. Two arrows are shown perpendicular to S, n hat equal to k hat and vector E equal to cy squared k hat. These point in the positive z direction.
Since the electric field is not constant over the surface, an integration is necessary to determine the flux.

Strategy

Apply Φ = S E · n ^ d A . We assume that the unit normal n ^ to the given surface points in the positive z -direction, so n ^ = k ^ . Since the electric field is not uniform over the surface, it is necessary to divide the surface into infinitesimal strips along which E is essentially constant. As shown in [link] , these strips are parallel to the x -axis, and each strip has an area d A = b d y .

Solution

From the open surface integral, we find that the net flux through the rectangular surface is

Φ = S E · n ^ d A = 0 a ( c y 2 k ^ ) · k ^ ( b d y ) = c b 0 a y 2 d y = 1 3 a 3 b c .

Significance

For a non-constant electric field, the integral method is required.

Got questions? Get instant answers now!

Check Your Understanding If the electric field in [link] is E = m x k ^ , what is the flux through the rectangular area?

m a b 2 / 2

Got questions? Get instant answers now!

Summary

  • The electric flux through a surface is proportional to the number of field lines crossing that surface. Note that this means the magnitude is proportional to the portion of the field perpendicular to the area.
  • The electric flux is obtained by evaluating the surface integral
    Φ = S E · n ^ d A = S E · d A ,

    where the notation used here is for a closed surface S .

Conceptual questions

Discuss how would orient a planar surface of area A in a uniform electric field of magnitude E 0 to obtain (a) the maximum flux and (b) the minimum flux through the area.

a. If the planar surface is perpendicular to the electric field vector, the maximum flux would be obtained. b. If the planar surface were parallel to the electric field vector, the minimum flux would be obtained.

Got questions? Get instant answers now!

What are the maximum and minimum values of the flux in the preceding question?

Got questions? Get instant answers now!

The net electric flux crossing a closed surface is always zero. True or false?

true

Got questions? Get instant answers now!

The net electric flux crossing an open surface is never zero. True or false?

Got questions? Get instant answers now!

Problems

A uniform electric field of magnitude 1.1 × 10 4 N/C is perpendicular to a square sheet with sides 2.0 m long. What is the electric flux through the sheet?

Got questions? Get instant answers now!

Calculate the flux through the sheet of the previous problem if the plane of the sheet is at an angle of 60 ° to the field. Find the flux for both directions of the unit normal to the sheet.

Φ = E · A E A cos θ = 2.2 × 10 4 N · m 2 / C electric field in direction of unit normal; Φ = E · A E A cos θ = −2.2 × 10 4 N · m 2 / C electric field opposite to unit normal

Got questions? Get instant answers now!

Find the electric flux through a rectangular area 3 cm × 2 cm between two parallel plates where there is a constant electric field of 30 N/C for the following orientations of the area: (a) parallel to the plates, (b) perpendicular to the plates, and (c) the normal to the area making a 30 ° angle with the direction of the electric field. Note that this angle can also be given as 180 ° + 30 ° .

Got questions? Get instant answers now!

The electric flux through a square-shaped area of side 5 cm near a large charged sheet is found to be 3 × 10 −5 N · m 2 / C when the area is parallel to the plate. Find the charge density on the sheet.

3 × 10 −5 N · m 2 / C ( 0.05 m ) 2 = E σ = 2.12 × 10 −13 C / m 2

Got questions? Get instant answers now!

Two large rectangular aluminum plates of area 150 cm 2 face each other with a separation of 3 mm between them. The plates are charged with equal amount of opposite charges, ± 20 μ C . The charges on the plates face each other. Find the flux through a circle of radius 3 cm between the plates when the normal to the circle makes an angle of 5 ° with a line perpendicular to the plates. Note that this angle can also be given as 180 ° + 5 ° .

Got questions? Get instant answers now!

A square surface of area 2 cm 2 is in a space of uniform electric field of magnitude 10 3 N/C . The amount of flux through it depends on how the square is oriented relative to the direction of the electric field. Find the electric flux through the square, when the normal to it makes the following angles with electric field: (a) 30 ° , (b) 90 ° , and (c) 0 ° . Note that these angles can also be given as 180 ° + θ .

a. Φ = 0.17 N · m 2 /C;
b. Φ = 0 ; c. Φ = E A cos 0 ° = 1.0 × 10 3 N / C ( 2.0 × 10 −4 m ) 2 cos 0 ° = 0.20 N · m 2 / C

Got questions? Get instant answers now!

A vector field is pointed along the z -axis, v = α x 2 + y 2 z ^ . (a) Find the flux of the vector field through a rectangle in the xy -plane between a < x < b and c < y < d . (b) Do the same through a rectangle in the yz -plane between a < z < b and c < y < d . (Leave your answer as an integral.)

Got questions? Get instant answers now!

Consider the uniform electric field E = ( 4.0 j ^ + 3.0 k ^ ) × 10 3 N/C . What is its electric flux through a circular area of radius 2.0 m that lies in the xy -plane?

Φ = 3.8 × 10 4 N · m 2 / C

Got questions? Get instant answers now!

Repeat the previous problem, given that the circular area is (a) in the yz -plane and (b) 45 ° above the xy- plane.

Got questions? Get instant answers now!

An infinite charged wire with charge per unit length λ lies along the central axis of a cylindrical surface of radius r and length l . What is the flux through the surface due to the electric field of the charged wire?

E ( z ) = 1 4 π ε 0 2 λ z k ^ , E · n ^ d A = λ ε 0 l

Got questions? Get instant answers now!

Questions & Answers

I'm interested in biological psychology and cognitive psychology
Tanya Reply
what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
Amanyire Reply
why is communication effective
Dakolo Reply
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
Wekolamo Reply
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Manix Reply
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
Amesalu Reply
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
Zyryn Reply
good👍
Jonathan
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
Kelu Reply
interpersonal relationships
Abdulfatai Reply
What would be the best educational aid(s) for gifted kids/savants?
Heidi Reply
treat them normal, if they want help then give them. that will make everyone happy
Saurabh
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 3

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'University physics volume 2' conversation and receive update notifications?

Ask