D2b - The Electric field

• Physics
• Secondary Education

Learning Objective

At the end of the lesson, you will understand the qualitative and mathematical definition of the electric field, the shape around point charges, uniform electric fields between parallel plates, and the vector nature of the electric field.

Mathematical Definition

The electric field (E) at a point is defined as the force (F) experienced by a positive test charge (q) placed at that point, divided by the magnitude of the test charge: E = F / q.

Please make a note of this defintion and annotate your data booklet.

If a +10 C charge is placed in an electric field and experiences a 50 N force, what is the electric field strength at the point where the charge is?

1. 500N/C
2. 1/5 N/C
3. 5 N/C
4. 50 N/C

Two equal positive point charges are placed near each other. Considering the E field of each charge sketch the resultant E feild around the two charges

Suppose that the force two point charges are exerting on one another is F. What is the force when one charge is tripled, the other is doubled, and the distance is cut in half ?

1. 3F
2. 3F/2
3. 6F
4. 24F

Note that for a uniform field such as the one below we can determine the Electric Field (E) if we know the Potential Difference between the two plates (V) and the separation distance (d)

E=​d​​V​​

Note: we will look at potential difference in more detail elsewhere.

The positive charge has a larger magnitude compared to the negative. Using the idea of Electric Field superposition explain the shape of the field at A and B.

A

B

1. A
2. B
3. C
4. D

1. X and Y only
2. Z and Y only
3. X and Z only
4. X, Y and Z

1. A
2. B
3. C
4. D

Write down 2 things you learned in this lesson.

Have students enter three things they learned in this lesson. With this they can indicate their own learning efficiency of this lesson.

Write down 2 things you want to know more about.

Here, students enter two things they would like to know more about. This not only increases involvement, but also gives them more ownership.

Ask 1 question about something you haven't quite understood yet.

The students indicate here (in question form) with which part of the material they still have difficulty. For the teacher, this not only provides insight into the extent to which the students understand/master the material, but also a good starting point for the next lesson.