goal to understand what electric force is and how to calculate it
Download
Skip this Video
Download Presentation
Goal: To understand what electric force is and how to calculate it.

Loading in 2 Seconds...

play fullscreen
1 / 12

Goal: To understand what electric force is and how to calculate it. - PowerPoint PPT Presentation


  • 112 Views
  • Uploaded on

Goal: To understand what electric force is and how to calculate it. Objectives: Understanding how to translate electric field to force Understand how to calculate Electric forces Knowing what Electric Field lines are and how to use them

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Goal: To understand what electric force is and how to calculate it.' - rafiki


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
goal to understand what electric force is and how to calculate it

Goal: To understand what electric force is and how to calculate it.

Objectives:

Understanding how to translate electric field to force

Understand how to calculate Electric forces

Knowing what Electric Field lines are and how to use them

Understanding motions of a charged particle in a constant electric field.

yesterday
Yesterday:
  • We learned that the Electric field is a topography of electric charges around you.
  • At any point the electric field is just a sum of the topography from each charge.
  • For each charge E = -qk / r2
  • How would this translate to a force?
ball downhill
Ball downhill
  • If you have a gravitational topography a ball will want to roll downhill.
  • That is it will roll from a high elevation to a low one or a high field to a low one.
  • The same is true of electric fields.
  • A positive charge will want to move to a lower electric field.
  • A negative charge will do the opposite and will want to move up to a higher valued electric field (moving uphill).
now for the math
Now for the math
  • The force on a charge is:
  • F = E * qon
  • Where qon is the charge the force is being applied to and E is the electric field that charge qon is located at.
  • Much like for gravity that F = m * g on the surface of the earth.
if we add in e
If we add in E
  • If we have 2 charges called qon and qby then the force is:
  • F = qon * E, but E = -qby k / r2
  • So, F = -qon * qby * k / r2
  • (k is the same constant we had before)
  • And if there are more than 2 charges, each charge will have a force on qon.
  • The net force will add up just like you add them up for E.
using the vectors
Using the vectors
  • The vector way to find the force:
  • Fx = -k qon * qby * x / r3 (x hat)
  • Fy = -k qon * qby * y / r3 (y hat)
  • Sanity check: like charges repel and opposites attract. The sign and direction should reflect that.
2 dimensions
2 dimensions
  • Just like yesterday in 2 dimensions you have to take the dimensions into account.
  • We will start off with a straightforward 3 charge problem.
  • q2 = 5 C and is at y = 3, X = 0
  • q3 = 9 C and is located at y = 0, x = 6
  • What is the total force on q1 if it is at the origin and has charge of 3 C?
now we take the next step
Now we take the next step
  • Now a little bit harder.
  • q2 = 3 C is at y = -2, x=0
  • q3 = -5 C and is at x = 3, y = -4
  • q1 = -2 C and is at the origin
  • What is the vector form of the force and what is the magnitude of the force on q1?
field lines
Field lines
  • Another way to look at this is by looking at field lines.
  • Field lines point downhill – the direction a positive charge will flow.
  • While these lines will tend to move towards – charges and away from + charges, that is not always the case if you have many charges.
  • (draw on board)
motions of a charge in a uniform electric field
Motions of a charge in a uniform electric field
  • Imagine you have an entire room where at any point in that room the electric field is about the same.
  • If you put a charge into that room then what will the charge do?
  • A) do nothing – no movement
  • B) move around in a circle
  • C) move around the room in random way
  • D) accelerate in some direction at a constant rate
  • E) accelerate in some direction in an ever increasing rate
motions of a charge in a uniform electric field1
Motions of a charge in a uniform electric field
  • Imagine you have an entire room where at any point in that room the electric field is about the same.
  • If you put a charge into that room then what will the charge do?
  • A) do nothing – no movement
  • B) move around in a circle
  • C) move around the room in random way
  • D) accelerate in some direction at a constant rate
  • E) accelerate in some direction in an ever increasing rate
  • Since F = q * E that already tells you the force will be a constant because q and E are constant here.
  • Also, ALWAYS remember that F = ma…
  • So, F = q * E = ma
  • So a = q * E / m for a uniform electric field!
  • Thus the acceleration is constant and the direction will be determined by the charge and the direction of the electric field.
conclusion
Conclusion
  • F = q * E
  • Electric Field lines point downhill.
  • If E is uniform then F and a are constants!
  • Once again the hardest part is doing the geometry.
ad