Question

You bring a negatively charged rubber rod close to a grounded conductor without touching it. Then you disconnect the ground. What is the sign of the charge on the conductor after you remove the charged rod? a) negative d) cannot be determined from b) positive the given information c) no charge

Short answer

Answer: b) positive

Step-by-step solution

Understand grounding and induction

When a negatively charged rubber rod is brought close to a conductor, the electrons in the conductor are repelled by the negatively charged rod and move away from it. This results in a separation of charges within the conductor, with the side closer to the charged rod being positively charged (due to the lack of electrons) and the other side being negatively charged (due to an excess of electrons). This process is called induction.

Grounding the conductor

When the conductor is connected to the ground, it allows electrons to flow between the conductor and the ground. In this case, because the side of the conductor farther from the rod is negatively charged (there are excess electrons), those excess electrons will flow into the ground, leaving the conductor with an overall positive charge.

Disconnecting the ground and removing the charged rod

Once the ground connection is removed, the flow of electrons between the conductor and the ground stops. This means the conductor retains its positive charge. After removing the charged rod, the conductor remains positively charged.

Determine the sign of the charge on the conductor

Based on the previous steps, at the end of the process, the conductor is left with a positive charge. Therefore, the correct answer is: b) positive

Key concepts

Grounding in Physics

Grounding is a fundamental concept in electrostatics that refers to the process of connecting an electrical device to the earth. This connection allows excess charge to flow into or out of the device, neutralizing it. Imagine grounding as a safety valve in a water system - it provides a pathway for excess electrons (or a shortage of them) to balance the system when connected.

In the context of electrostatic induction, when a conductor is grounded, electrons can move freely between the conductor and the earth. If there's an excess of electrons, they flow into the ground, leaving the conductor with fewer negative charges. Conversely, if the conductor has too few electrons, electrons can flow from the ground into the conductor to balance the charge. This process helps achieve electrostatic equilibrium.

For example, when a negatively charged rod is brought near a conductor, the grounding process allows excess electrons in the conductor to escape to the ground, resulting in the conductor becoming positively charged once the ground connection is severed.

Charge Separation

Charge separation is a crucial aspect of electrostatic induction. When a charged object is brought near a conductor, it induces a separation of charges within the conductor without direct contact.

Here's how it works:

• A negatively charged rod brought near a conductor will repel electrons in the conductor, causing them to move away from the source of the negative charge.
• This movement results in one side of the conductor becoming positively charged (because it has lost electrons) and the other side negatively charged (because it holds more electrons).

This leaves the conductor with two charged regions, positive and negative. However, the conductor as a whole remains electrically neutral unless grounded. If grounding occurs at this point, electrons can leave the negatively charged region, leading to a net positive charge.

It's essential to remember that charge separation does not change the total charge of the object until grounding or another external influence alters it.

Electrophysics

Electrophysics deals with the study of electric charges, electric fields, and the forces arising from them. It explains phenomena like electrostatic induction, grounding, and charge separation in a systematic way. This branch of physics clarifies how charged objects interact in various setups and conditions.

In electrostatics, one of the main focus areas of electrophysics, the objects in consideration typically hold static (constant) charges. When a charged object influences a nearby conductor without contact - a process known as electrostatic induction - it perfectly exemplifies the principles of electrophysics. The conductor's electrons rearrange, reacting to the electric field from the charged object.

Electrophysics equips us with equations and concepts to predict and describe these interactions. For instance, Coulomb's Law helps calculate the force between two charges, while Gauss's Law relates the distribution of electric charge to the resulting electric field. These principles are foundational for understanding not just simple charge interactions, but also their applications in technologies like capacitors and electronic circuits.