Physics 203 Midterm I-Questions 2025/2026 with
100% Correct Solutions
Immediately after a plastic rod is given a net negative charge by rubbing it with fur, the fur
has an equal positive charge.
A comb is given a net electric charge. Which of the following will allow you to determine
the sign of the charge?
The comb attracts an object known to have a positive charge AND the comb repels an object
known to have a negative charge
A positively charged rod is brought close to a neutral piece of paper, which it attracts. The
positively charged rod is removed, the paper is grounded to make it neutral again, and a
negatively charged rod is brought close to the piece of paper. The negatively charged rod
attracts the piece of paper
The force between two point charges is 1 N. The charges are moved so they are four times
as far apart. The force between the charges is now
1/16 N
A -1.0 μC point charge is placed at a point where it experiences an electric force of 0.025 N,
down. The electric field at that point is
25,000 N/C up
Why can't electric field lines cross?
, At the point where they cross the field would have two different directions at the same time,
which isn't possible.
In each of the following cases, equal magnitude positive and negative point charges are
placed at the positions shown. In which case will the magnitude of the electric field at the
black dot be zero?
negative negative with the dot in the middle
In each of the following cases, equal magnitude positive and negative point charges are
placed at the positions shown. In which case will the magnitude of the electric field at the
black dot be the greatest?
opposite charges with the dot in the middle
Why is the inside of a car a safe place to be during a thunder and lightning storm?
The car is metal. The electrostatic field inside a conductor is zero.
What is the main advantage of using electric potential instead of electric potential energy?
The potential of a point in space is independent of the sign of the charge placed at that point.
A charge is initially at rest in an electric field. Which of the following correctly describes
how the charge will move?
A negative charge will move from lower to higher potential; a positive charge will move from
higher to lower potential.
What is the direction of the electric field in a parallel plate capacitor?
From the positive plate to the negative plate AND from high potential to low potential.
100% Correct Solutions
Immediately after a plastic rod is given a net negative charge by rubbing it with fur, the fur
has an equal positive charge.
A comb is given a net electric charge. Which of the following will allow you to determine
the sign of the charge?
The comb attracts an object known to have a positive charge AND the comb repels an object
known to have a negative charge
A positively charged rod is brought close to a neutral piece of paper, which it attracts. The
positively charged rod is removed, the paper is grounded to make it neutral again, and a
negatively charged rod is brought close to the piece of paper. The negatively charged rod
attracts the piece of paper
The force between two point charges is 1 N. The charges are moved so they are four times
as far apart. The force between the charges is now
1/16 N
A -1.0 μC point charge is placed at a point where it experiences an electric force of 0.025 N,
down. The electric field at that point is
25,000 N/C up
Why can't electric field lines cross?
, At the point where they cross the field would have two different directions at the same time,
which isn't possible.
In each of the following cases, equal magnitude positive and negative point charges are
placed at the positions shown. In which case will the magnitude of the electric field at the
black dot be zero?
negative negative with the dot in the middle
In each of the following cases, equal magnitude positive and negative point charges are
placed at the positions shown. In which case will the magnitude of the electric field at the
black dot be the greatest?
opposite charges with the dot in the middle
Why is the inside of a car a safe place to be during a thunder and lightning storm?
The car is metal. The electrostatic field inside a conductor is zero.
What is the main advantage of using electric potential instead of electric potential energy?
The potential of a point in space is independent of the sign of the charge placed at that point.
A charge is initially at rest in an electric field. Which of the following correctly describes
how the charge will move?
A negative charge will move from lower to higher potential; a positive charge will move from
higher to lower potential.
What is the direction of the electric field in a parallel plate capacitor?
From the positive plate to the negative plate AND from high potential to low potential.
