Pre Lab
As discussed in last week's lab, electric charges feel attractive and repulsive forces as determined by Coulomb's Law. Two positively charged objects will feel a force pushing them apart. Like gravity, this electric force acts at a distance, not requiring any physical contact between the objects acting on each other. We call this a "field force" as we use the idea of an electric field to help us make sense of how charged objects behave near another charged object(s). The concept of an electric field was introduced by Michael Faraday. He said that an electric field is emanated out from positively charged items and into negatively charged items. They are vector quantities that emanate out (or in) in all directions and can be represented by lines as shown in the picture below.
The electric field is NOT a force but defines the forces that charged particles would feel at specific points in space. The field lines describe the direction that a positive test charge will feel electrical force at a given point.
Electric fields add vectorially. When you have multiple charges located in an area, their fields will add as vectors. This is part of the principle of Superposition which is REALLY important in studying electricity and magnetism. Below is a diagram of a Dipole (a positive and negative charge together). And here is a diagram for a line of positive charges.
We can get the equation for the field strength near a point charge from Coulomb's Law as follows.
This equation works great for point charges, but charge distributions (where the charge is spread out in a shape) require so high level math, specifically integration. Here are a couple links to examples using a line of charge:
The videos to the right do a pretty good job of describing all of these points in greater detail so be sure to check them out. In the lab this week we will apply this principle and a simulation (one of the ones we played with in last week's prelab) to describe the electric field produced by various arrangements of charges. Prior to lab please complete the following:
|
Electric Field Videos from Khan Academy
Professor Dave Explains Electric Fields
Crash Course on Electric Fields
E Field Due to a Line of Charge
|
Pre Lab Video
Simulation
Explore the simulations embedded at the following links to explore factors regarding electric fields and forces. These were both included last week, but we will be looking at the fields this time.
Simulation 1: https://phet.colorado.edu/sims/html/charges-and-fields/latest/charges-and-fields_en.html
Simulation 2: https://phet.colorado.edu/en/simulation/electric-hockey
Simulation 3: http://www.physicsclassroom.com/Physics-Interactives/Static-Electricity/Put-the-Charge-in-the-Goal
You may use the simulation to answer the pre lab quiz questions as well.
Pre-Lab Quiz is available at the course Blackboard website
Simulation 1: https://phet.colorado.edu/sims/html/charges-and-fields/latest/charges-and-fields_en.html
Simulation 2: https://phet.colorado.edu/en/simulation/electric-hockey
Simulation 3: http://www.physicsclassroom.com/Physics-Interactives/Static-Electricity/Put-the-Charge-in-the-Goal
You may use the simulation to answer the pre lab quiz questions as well.
Pre-Lab Quiz is available at the course Blackboard website
Lab
This week you will be completing the Charges and Electric Fields lab (pg.11) found your lab manual.
We will be using a Phet simulation on the lab computers to complete this lab.
We will be using a Phet simulation on the lab computers to complete this lab.
Post Lab
Please post a reflection on the lab experience on the Charges and Electric Fields Reflection discussion board on the course Blackboard site.
Be sure to include:
Be sure to include:
- What you did
- Why you did it
- Any interesting observations
- What you learned from doing the lab