Problem 99 - University Physics with Modern Physics

Question

What is the best explanation for the observation that the electric charge on the stem became positive as the charged bee approached (before it landed)? (a) Because air is a good conductor, the positive charge on the bee's surface flowed through the air from bee to plant. (b) Because the earth is a reservoir of large amounts of charge, positive ions were drawn up the stem from the ground toward the charged bee. (c) The plant became electrically polarized as the charged bee approached. (d) Bees that had visited the plant earlier deposited a positive charge on the stem.

Step-by-Step Solution

Answer

The best explanation is option (c): plant polarization.

Step 1: Understanding the Question

We need to determine which choice explains why the electric charge on the plant stem became positive as a charged bee approached it, even before the bee landed.

Step 2: Analyzing Option (a)

Option (a) suggests that the charge was transferred through the air because air is a good conductor. However, air is actually a poor conductor, making this option unlikely to explain the observation.

Step 3: Analyzing Option (b)

Option (b) claims positive ions are drawn up the stem from the ground. While the Earth is a charge reservoir, this option implies charge movement that’s not typically how charge redistribution due to external fields occurs.

Step 4: Analyzing Option (c)

Option (c) involves polarization, where the charged bee induces a separation of charges in the plant, leading to charges on the stem becoming positive near the bee without direct contact. This explanation aligns with known physical behavior of polarization.

Step 5: Analyzing Option (d)

Option (d) states that previous bees left a positive charge on the stem. However, this doesn’t explain why the charge became positive as the current bee approached.

Step 6: Conclusion

The best explanation is option (c): The plant became electrically polarized as the charged bee approached, causing charges to rearrange and the observed positive charge on the stem.

Key Concepts

Electric Charge

Electric charge is one of the fundamental properties of matter. It comes in two types: positive and negative. Objects become charged when they gain or lose electrons, the negatively charged particles that orbit an atom's nucleus.

If an object gains electrons, it becomes negatively charged, whereas if it loses electrons, it becomes positively charged.

• Like charges repel each other.
• Opposite charges attract each other.

These interactions are what lead to various phenomena, including electric forces and the ability of charged objects to exert force over a distance.

Conductors and Insulators

Materials can be classified as conductors or insulators based on their ability to allow electric charge to move through them. Conductors, like metals, allow charges to flow freely. This is because they have free electrons that can move easily within the material’s structure.

On the other hand, insulators, such as rubber or glass, do not allow charge to flow easily. This is because their electrons are tightly bound to their atoms, making movement difficult.

• Conductors: Facilitate easy movement of charge.
• Insulators: Restrict the movement of charge.

Understanding the nature of conductors and insulators helps in explaining how charge can build up on an object or get transferred between them.

Charge Redistribution

Charge redistribution occurs when charges within a conductor move in response to other nearby charges. When a charged object is brought near a conductor, the free electrons in the conductor move, causing a shift in charge distribution.

This process is especially important in explaining how conductive materials can become polarized. Charge redistribution does not necessarily mean the conductor gains or loses charge but rather that charges within it realign under external influence. Consequently, this can result in localized regions of positive or negative charge depending on where the external charge is positioned relative to the conductor.

Induced Charge Separation

Induced charge separation is the process by which a charged object causes a redistribution of charges within another object, even without directly touching it. When a charged object, like a bee, approaches a neutral object, like a plant stem, it can cause the charges in the neutral object to rearrange.

In this case, the charged bee induces positive and negative charges to separate within the plant, resulting in one side of the plant becoming positively charged and the other negatively charged. This polarization effect is a crucial concept in understanding how objects can influence each other's electrical state from a distance, aligning with option (c) from the exercise. This happens because electric fields from charges extend into space and exert forces on electric charges over distances.