ElectromagnetismLesson 4 of 7 in the course Electric Charges and Fields

Electric Fields: Point Charges, Superposition, and Direction

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces the electric field as a useful way to describe how source charges influence the space around them. Instead of recalculating the force for every test charge, we can find the field once and use it to determine the force on any charge placed at a point.

A source charge produces an electric force on another charge. For several source charges, the net force on a test charge is the vector sum of the individual forces. Since each electrostatic force is proportional to the test charge QQ, the net force can be written as F⃗=QE⃗\vec{F}=Q\vec{E}.

All flashcards

What is the electric field?
Electric force per unit positive test charge at a location, written E⃗=F⃗/Q\vec{E}=\vec{F}/Q.
What determines an electric field?
The source charges and their positions relative to the point where the field is evaluated.
How do you find the force on a charge in a known electric field?
Use F⃗=QE⃗\vec{F}=Q\vec{E}; a negative charge experiences force opposite the field direction.
What is the field of a point charge?
For charge qq, E⃗=k(q/r2)r^\vec{E}=k(q/r^2)\hat{r}, where r^\hat{r} points from the source toward the observation point.
What is the observation point in an electric-field calculation?
The location at which the field is evaluated; displacement vectors run from each source to this point.

Quiz questions

  1. When several source charges contribute to the electric field at a point, how is the total field found?Answer: By adding the individual field vectors.
  2. Which statement correctly classifies the electric field and temperature?Answer: Electric field is a vector field; temperature is a scalar field.
  3. A negative charge is placed in an electric field. In which direction is the electric force on it?Answer: Opposite to the direction of the electric field.
  4. What are the SI units of electric field?Answer: Newtons per coulomb (N/C).
  5. In electrostatics, how is the Coulomb constant kk defined in terms of vacuum permittivity ϵ0\epsilon_0?Answer: k=14πϵ0k=\frac{1}{4\pi\epsilon_0}

Based on University Physics Volume 2 by Samuel J. Ling, William Moebs, Jeff Sanny (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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