The following electric field problems will help you sharpen your knowledge of electric field.
Things that you absolutely need in order to solve the problems on this lesson.
Know how to draw the electric field vector.
Know how do solve math problems that have multiplication and division of exponents.
Convert d to meter before doing the math.
The electric field unit is N/C
Problem #1
A particle with charge q = 5Q is placed at a distance d from a point A.
1. Calculate the electric field produced at the point A in terms of k, Q and d.
Solution
When solving electric field problems, you need to find the magnitude and the direction of the electric field. You cannot just look for one and forget about the other.
To find the magnitude, use the formula shown above.
To find the direction, put a small positive test charge in the field and then find out if it will be attracted or repulsed.
For this problem it is very easy to find the magnitude of the electric field. Just substitute 5Q for q. The next two electric field problems will take things to the next level.
Put the test charge at point A. The direction of the electric field is shown below.
Caution
Take your time when reading the following electric field problems. Do not rush it!
E_{1} = k
4Q
d^{2}

E_{2} = k
8Q
d^{2}

Since the denominator is the same, we can just add 4Q and 8Q.
4Q + 8Q = 12Q
Put the test charge at point A. The direction of the electric field is shown below with the brown arrow.
Notice how the brown vector is the result of adding the green vector and the orange vector.
Notice also how the size of the orange vector is twice that of the green since 8Q is twice 4Q.
E_{1} = k
2Q
d^{2}

E_{1} = k
2Q
d^{2}

We need to add all the x components and all the y components for the two vectors (green and red).
When looking at the graph, I see that the y components are shown in gold and dark blue. Moreover, I immediately see that the y components add up to zero.
For both the green and the red vector, the x components is the blue line.
Find the x component of the green vector
To Find the x component of the red vector, we basically repeat what we did for the green vector to end up with the exact same answer.
Perhaps the last two electric field problems were hard. Send your questions.
Mar 16, 17 03:15 PM
Great lesson about the law of reflection. Crystal clear explanation
New! Comments
Do you like the physics lessons on this site? Have your say about what you just read! Leave me a comment in the box below. Please share the lessons with your friends as well!