Combining Electric Fields
Combining Electric Fields
- Electric field strength is a vector. Draw the direction from each source charge before deciding whether magnitudes add or subtract.
Add electric fields as vectors
- At the point of interest, draw one field arrow for each source charge.
- Calculate each magnitude separately.
- Add fields that point in the same direction. Subtract fields that point in opposite directions.
Opposite-sign charges
Between the charges, both field arrows point from positive to negative, so the magnitudes add.
Same-sign charges
Between the charges, the field arrows oppose, so the magnitudes subtract.
Common mistake
Do not decide “add or subtract” from the charge signs alone. Draw the field arrows at the point first.
Your turn9702/41/O/N/24 Q5(c)
A point lies between a positive charge and a negative charge. Do the two field magnitudes add or subtract? Explain using direction.
Show worked answer
Both field arrows point from the positive charge towards the negative charge, so the magnitudes add.