Unit 7 Test Review: Electrostatics

A positively charged rod is brought near the knob, but does not touch a neutral electroscope. Which of these four pictures represents the charge distribution on the knob and foil leaves of the electroscope as the rod is held nearby?

• A

• B

• C

• D

Answer explanation

When a positively charged rod is brought near the neutral electroscope, electrons in the knob are attracted towards the rod, causing the knob to become negatively charged and the leaves to become positively charged. This is represented in choice D.

What charge does an object have if it loses electrons?

• positive charge

• negative charge

• no charge

Answer explanation

An object that loses electrons has a deficiency of negatively charged particles. This results in a net positive charge, as the positive charges from protons are no longer balanced by an equal number of electrons.

What happens to the potential energy as a negative charge is brought closer to another negative charge?

• It remains constant

• It decreases

• It increases

Answer explanation

As a negative charge approaches another negative charge, the repulsive force increases, leading to an increase in potential energy. Therefore, the correct answer is that the potential energy increases.

Tags

NGSS.HS-PS2-4

A child slides down a plastic slide at the playground and becomes charged with her hair standing on end. Which method of charging did she experience?

• Friction - electrons got transferred between the slide and the child as she slid down.

• Induction - the child got near the slide and electrons were transferred.

• Conduction - the child simply touched the slide and electrons were transferred to her hair.

Answer explanation

The child experienced charging by friction as she slid down the plastic slide, causing electrons to transfer between her hair and the slide, resulting in her hair standing on end.

A student conducting a static electricity investigation charges a neutral metal ball by touching it with a charged rod. Which statement correctly describes the results of this investigation? Think of what happened in the John Travoltage Lab.

• The charges will stay right where the rod touched because it is a conducting material.

• The charges will spread out in the metal ball because it is a conducting material.

• The charges will spread out in the metal ball because it is an insulating material.

• The charges will stay right where the rod touched because it is an insulating material.

Answer explanation

The charges will spread out in the metal ball because it is a conducting material. Conductors allow charges to move freely, so when the charged rod touches the ball, the charges distribute evenly across its surface.

Tags

NGSS.MS-PS2-5

Which of the following materials is a conductor of electricity?

• glass

• metal

• rubber

• plastic

Answer explanation

Metal is a good conductor of electricity due to its free-moving electrons, allowing electric current to flow easily. In contrast, glass, rubber, and plastic are insulators and do not conduct electricity.

Two balloons are charged and hung from strings as shown to the right. They are repelling each other. Which statement is true?

• They must have opposite charges.

• They must have like charges.

• Their charge cannot be determined from the information provided.

Answer explanation

The balloons are repelling each other, which indicates they must have like charges. Opposite charges would attract, not repel. Therefore, the correct statement is that they must have like charges.

Tags

NGSS.MS-PS2-3

Physics students studied various behaviors and features of charged particles and how they interact with other charged materials. The image below shows the results of sending a charged particle through two oppositely charged electric plates. What is the charge on the particle moving between the two electrically charged plates shown based on its movement?

• positive

• negative

• neutral

• cannot be determined

Answer explanation

The charged particle moves towards the positively charged plate, indicating it has a negative charge. Positive charges would move away from the positive plate, while neutral particles would not be affected.

Tags

NGSS.MS-PS2-3

NGSS.MS-PS2-5

NGSS.MS-PS2-2

What happens to the electrical force between two charges held some distance apart, if the value of BOTH of the charges doubles?

• ¼ Fe

• ½ Fe

• 4 Fe

• ½ Fe

Answer explanation

According to Coulomb's law, the electrical force (Fe) is directly proportional to the product of the charges. If both charges double, the force becomes 4 times greater, resulting in 4 Fe.

Tags

NGSS.HS-PS2-4

Which answer most completely describes the difference(s) between the gravitational force and the electrostatic force?

• The gravitational force is much weaker than the electrostatic force.

• The gravitational force can only attract but the electrostatic force can attract or repel.

• The gravitational force occurs throughout the universe but the electrostatic force only occurs on Earth.

• The gravitational force is weaker and can only attract objects but the electrostatic force is strong and can both attract and repel.

Answer explanation

The correct choice highlights that the gravitational force is weaker and only attracts, while the electrostatic force is stronger and can both attract and repel, accurately describing their fundamental differences.

Tags

NGSS.HS-PS2-4