How to Draw Electric Field Lines for Two Particles with Different Magnitude Charges

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Shorouq Ahmad graduated from Middle Tennessee State University where they majored in Applied Physics and completed the Pre-Med program. Shorouq taught and designed Physics courses for 6+ years to varying levels and has taught AP Physics.

Leah Simon has a Ph. D. in Astronomy from the University of Florida and a Bachelor of Arts degree in Physics from Macalester College. She has taught college physics and astronomy for over 10 years and has worked for several years as a lesson writer for high school and college physics laboratory courses.

Step 1: Identify the signs of the charges on each particle.

Step 2: Determine the ratio of the magnitudes of the charges on each particle.

Step 3: Draw electric field lines pointing toward or away from each particle, with the number of lines on each particle proportional to the ratio found in the previous step.

What is an Electric Field Line?

Electric Field Line: A line that indicates the direction of the electric field at a certain location near a charged object. Electric fields point away from positive charges and toward negative charges. The number and density of electric field lines indicate the magnitude of the charge and the strength of the electric field, respectively. Electric field lines are symmetric around a point charge in isolation, radiating from the charge in all directions. Electric field lines cannot cross one-another.

Point Charge: A charge that resides at a single point in space and does not have dimensions.

Let’s try drawing electric field lines for some example point charges with different magnitude charges. The first example has two charges of the opposite sign. The second example has two charges of the same sign.

Examples of How to Draw Electric Field Lines for Two Particles with Different Magnitude Charges

Example 1

Draw the electric field for a +2 point charge located next to a -5 point charge.

Step 1: Identify the signs of the charge on each particle.

The signs of the charges are given in the text of the problem. One charge is positive and one is negative. The electric field will point away from the positive charge and toward the negative charge.

Step 2: Determine the ratio of the magnitudes of the charges on each particle.

One charge has an absolute value of 2 and the other has an absolute value of 5. The ratio of the charges is 2 to 5.

Step 3: Draw electric field lines pointing toward or away from each particle, with the number of lines on each particle proportional to the ratio found in the previous step.

If we choose to draw 4 electric field lines pointing away from the positive charge, there must be 2 x 5 = 10 electric field lines pointing toward the negative charge.

Here is how the electric field will look.

Electric field lines for +2 and -5 point charges.

Electric Field lines for +2 and -5 point charges

Example 2

Draw the electric field for a point charge with charge +10 that is nearby a point charge with a charge +14.

Step 1: Identify the signs of the charges on each particle.

Both particles in this problem have a positive charge, so the electric field will point away from both charges.

Step 2: Determine the ratio of the magnitudes of the charges on each particle.

One particle has a charge of absolute value 10 while the second particle has a charge of absolute value 14. The ratio of the charges is 10 to 14 which reduces to 5 to 7.

Step 3: Draw electric field lines pointing toward or away from each particle, with the number of lines on each particle proportional to the ratio found in the previous step.

We can choose to draw 5 electric field lines radiating away from the first charge and 7 radiating away from the second charge. The lines cannot cross, so between the two charges, they will curve away, leaving a gap between the two particles with no electric field lines.

Here is how the electric field will look.

Electric field lines for +10 and +14 point charges.