Cuesta College, San Luis Obispo, CA
Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing presentations on charges and materials and electric forces and fields.
Selected/edited responses are given below.
Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Electrons are free to move in conductors, whereas in an insulator electrons are more or less fixed to their location. For insulators, when a charged object is introduced, particles of the opposite charge are drawn to the object. For conductors, particles will actually separate creating a positive half and negative half that is dependent on the orientation of the object introduced."
"The positive charge of a proton equals the negative charge of an electron. The law of conservation of electric charge says the net electric charge of an isolated system remains conserved. Coulomb's law is the force that charges exert on each other."
"When positive or negatively charged objects get close to an insulator or conductor, the electrons will move accordingly in order to create a net attraction to the object."
"Neutral objects will have an electrostatic attraction to objects that are charged. The attraction will be the same for positively or negatively charged objects."
"The greater the charges and the closer together they are, the greater the force. Unlike signs are attracted, like signs are repelled."
"Electrons are able to transfer between objects through the air. This is done by an electric shock or arc, where several electrons all jump at the same time along the path of least resistance."
"The electric force between charges is directly proportional to the product of the absolute value of the charges and a constant (k) and inversely proportional to the square of the distance between the charges. As the distance between the charges increases, the force decreases. As the distance between the charges decreases, the force between the charges increases."
"The difference between electric force and electric fields, and how to solve for them. A simple equation for force, and a two-step process for electric fields."
Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"A lot of chemistry concepts overlapped--I would like clarification on the gasoline and electric spark question."
"I don't quite understand how something that is a neutral insulator can be attracted to a charge I would assume it would want to keep its neutral balanced state."
"What does Q mean?"
"The concept of a test charge, q was confusing. I do not understand how the electric field is a vector."
"I am pretty confused about source charges and the field model. I understand that one source will exert a force on another but I got lost when we started talking about source charge Q creating an electric field."
"Coulomb's law. Also the field model: electric fields, electric forces, and source and test charges."
"The difference between electric force and electric field. I feel like I understand the definition of each, but I am unsure of how they relate to one another."
"The field model looks pretty confusing based on all the variables but I think will be easier to understand in lecture with examples."
"The test charge--I do not understand how it is a test charge and what exactly is being tested."
"Why does +q always has a force exerted on it along the direction of a field line and –q always has a force exerted on it against the direction of a field line?"
"I remember learning about this in a previous physics class so I understood most of it."
"When she sat in the car, the seat rubbed against her creating a charge, and her rubber shoes improperly grounded her, so when she touched the nozzle, static electricity was produced sparking a fire."
"She became electrically charged when she rubbed her hands on her sweater causing friction and transfer of charges."
"Nothing like fire to get the tough stains out, am I right?"
a positive. *** [3] a negative. **** [4] either a positive or a negative. ********************* [21] zero (neutral). ** [2] (Unsure/lost/guessing/help!) * [1]
a positive. ***** [5] a negative. ***** [5] either a positive or a negative. ******************* [19] zero (neutral). * [1] (Unsure/lost/guessing/help!) * [1]
a positive. *** [3] a negative. ********* [9] either a positive or a negative. ******************* [19] zero (neutral). * [1] (Unsure/lost/guessing/help!) * [1]
Explain the difference between units for electric force, F, and the electric field, E.
"Force F has units of N or newtons and electric field E has units of N/C or newtons per coulomb."Explain the conceptual difference between the electric force, F, and the electric field, E.
"Electrical field is proportional to the electrical force divided by the test charge. The direction of the electric field is the same direction of the force, they both are vectors."Explain the conceptual difference between a source charge (±Q), and a test charge (±q).
"Electric force is dependent on the force a source charge exerts on a test charge. Electric field is dependent on source charge creating an electric field around it."
"The electric field E is created by the source Q and then the electric force F is exerted by the electric field onto the test charge q."
"Electric force is the attraction or repulsive interaction between two objects. The electric field is the region around a charged object with which a force would be exerted on other charged particles."
"Not quite sure."
"Q exerts a field out around it and q obeys the force exhibited by the electrical field."
"A source charge Q is the one applying force onto source charge q. I am still a little confused with this stuff."
"Well the field is coming from the source charge, and the test charge is just something we use to see how it will react to the field."
"A source charge creates an electric field and the test charge is placed within the field. This is confusing to me, I think I would benefit from more visuals on this."
(Only correct responses shown.)
Positive source charge (+Q): E field lines point outwards [77%]
Negative source charge (–Q): E field lines point inwards [80%]
along the E field direction. ******************* [19] opposite the E field direction. ********** [10] (Unsure/guessing/lost/help!) ** [2]
A negative point charge (–q) is placed on an electric field line (due to some other source charge ±Q). This positive point charge will always experience an electric force F:
along the E field direction. ****** [6] opposite the E field direction. *********************** [23] (Unsure/guessing/lost/help!) ** [2]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"We HAVE to go over electric forces and fields. The whole presentation makes no sense to me."
"More explanation would be nice."
"Can we do some examples in class?"
"I'm sure we will go over the equations in class."
"Not exactly sure what to ask but I am a little confused. Hopefully more explanation in lecture will clear some things up."
"What will our next quiz be on?" (Interference and electrostatics. The study guide for next week's quiz is already posted.)
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