Electric Current (SAQs)

Physical Science | 9. Electric Current – SAQs:
Welcome to SAQs in Chapter 9: Electric Current. This page contains the most Important FAQs for Short Answer Questions in this Chapter. Each answer is provided in simple English, with a Telugu explanation, and formatted according to the exam style. This will support your preparation and help you secure top marks in your exams.

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SAQ-1 : Write two examples for ohmic and non-ohmic materials each.

Introduction

Materials can be classified based on their voltage-current relationship. Some materials, known as ohmic materials, have a linear relationship between voltage and current, meaning their resistance remains constant. On the other hand, non-ohmic materials have a non-linear relationship, indicating that their resistance varies.

Ohmic Materials

1. Definition: Ohmic materials obey Ohm’s Law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant.
2. Examples:
   • Metallic Conductors: Most metals, like copper or silver, show a linear V-I relationship under constant temperature, making them ohmic.
   • Carbon Resistors: These are specially designed resistors made of carbon and they obey Ohm’s Law within specific limits.

Non-Ohmic Materials

1. Definition: Non-ohmic materials don’t have a constant resistance. Their resistance varies with the current or voltage.
2. Examples:
   • Diodes: Diodes are semiconductor devices that allow current to flow in one direction only. Their V-I characteristics are non-linear, with current dramatically increasing after a certain threshold voltage.
   • Filament Bulbs: As the filament bulb heats up due to the current flow, its resistance changes, leading to a non-linear V-I characteristic curve.

Summary

While many materials exhibit a linear V-I relationship and obey Ohm’s Law, there are also plenty of materials with non-linear characteristics. Understanding the nature of these materials is essential in electronics and electrical engineering.

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SAQ-2 : Why doesn’t a bird get a shock when it stands on a high voltage wire?

Introduction

A common observation is that birds frequently perch on high voltage wires without getting electrocuted. This might seem puzzling given the high amount of voltage in these wires. The answer lies in the way electric current works and the concept of potential difference.

Understanding Potential Difference

1. Basics of Electricity:
   For an electric current to flow, there must be a potential difference, or voltage difference, across two points. The current will choose the path of least resistance between these points.
2. Parallel Lines:
   High voltage power lines usually run parallel to each other, carrying a significant voltage.
3. Contacting the Lines:
   A bird or any creature would only experience an electric shock if it creates a pathway for the current by touching two points with different voltages.

Birds on the Wire

1. Single Point of Contact:
   When a bird sits on a single wire, both its feet are at the same electrical potential, so there’s no potential difference across its body.
2. No Alternate Pathway:
   The bird doesn’t offer a more conducive pathway for the current. The electricity continues to flow along the wire, as that’s the path of least resistance.

Summary

Birds remain unharmed on high voltage wires because they don’t create a path for the current or establish a potential difference. It’s crucial to note that if the bird were to touch another wire or grounded structure while still in contact with the first wire, it would create a pathway for the current, leading to electrocution. This principle underlines the importance of understanding electrical safety.