Static Electricity Test Corrections
Use the following answer key and explanations to write up your test corrections. All corrections are due
by Monday the latest. If you have any questions, you can ask me in class tomorrow.
YOU WILL STILL HAVE A RESISTANCE QUIZ TOMORROW!!
Make sure that each correction explains how to get the correct answer and why your answer was
incorrect. Only responses that do both of these will receive credit. Between this and ‘Work, Power, and
Energy’, your best corrections will be used to give you credit.
Make sure you get all labs in by the end of the day Friday. All make-up work must be done by the week’s
end. E-mail me at wrockensies@sewanhaka.k12.ny.us if you are unsure of what you owe.
1. Since a positively charged object is brought near the Knob, electrons (negatives) move up to the
knob. This then causes the Leaves to lose electrons, becoming MORE positive, therefore the
separation increases.
2. If the electroscope is neutral, it should have EQUAL numbers of positives and negatives. When a
negatively charged object is brought near, the charges rearrange themselves so that the
electrons (negatives) are repelled down into the leaves, and the knob becomes positive.
3. When a neutral object makes contact with a charged object, the neutral object gains the same
charge as the positively charged object. Since the neutral object is now POSITIVE, it LOST
electrons.
4. Electroscopes detect charge, but don’t necessarily indicate whether it is positive or negative.
Compasses line up with magnetic field lines. Galvanometers (we call them ammeters) are used
to detect current. Voltmeters detect potential difference (Voltage).
5. When two objects are brought together, you sum the total charge. +2 + 0 = +2. When
separated, you must divide the total charge by 2. +2/2 = +1 on each object.
6. Since the pith ball is neutral, it gains the same charge as the positive rod, losing electrons.
7. Protons never move!! If the wool is positive, it must have lost electrons.
8. If the hair becomes positive, it is because it lost electrons
9. Add the charge, divide by two – SHOW THE WORK
10. Losing electrons leads to a positive charge
11. – 14. Convert each answer to elementary charges. Whichever answer is a whole number is
correct. All other answer choices have decimals, which is impossible since that indicates you
have only part of an electron/proton.
15. Find the charge on each sphere. A loses some of its charge, while B gains. This could only happen
if A gains electrons and B loses them.
16. They have the same charge before contact, so they will have the same charge when separated
17. Add the charges and divide by 2 – SHOW THE WORK!
18.-19. Use Coulomb’s Law – SHOW THE WORK
20. -22. Show how the factors change total force by replacing each variable with the factor it
changes by.
23. E and r have an inverse square relationship.
24.-26. Show how the factors change total force by replacing each variable with the factor it changes
by.
27.-28. Use the Electric Field Strength equation. SHOW THE WORK!
29. Electric field lines are drawn based on what a positive charge would do if placed in a certain
point in space. So around a negative charge, field lines point towards it because that is what would
happen if there was a positive charge in that position.
30. See explanation for 29, but switch it for a positive charge.
31. If a positive charge were placed at point A, where would it go?
32. Field lines ALWAYS point to the negative, away from the positive.
33. Electrons are attracted to the positive. Since it feels a FORCE (F=ma) it accelerates.
34. E field strength is uniform (the same) between two parallel plates.
35. Use E=F/q - SHOW THE WORK!