Direct Current (DC) MCQs Quiz | Class 10

This quiz on Direct Current (DC) MCQs is designed for Class X Science (Code 086) students, covering Unit IV: Effects of Current. It focuses on the definition and characteristics of Direct Current. Test your knowledge, submit your answers, and download a detailed PDF answer sheet for review.

Understanding Direct Current (DC)

Direct Current (DC) is a type of electric current that flows in a single, constant direction. Unlike Alternating Current (AC), which periodically reverses its direction, DC maintains a steady flow, making it essential for a wide range of electronic devices and applications. This section provides a detailed look into the definition, characteristics, and common uses of DC.

Definition of Direct Current (DC)

Direct Current (DC) is defined as the unidirectional flow of electric charge. This means that the electrons (or conventional current, which flows in the opposite direction of electrons) move consistently from a higher potential to a lower potential without changing their direction over time. The magnitude of DC can be constant (as from a battery) or it can vary, but its direction always remains the same.

Characteristics of Direct Current

  • Unidirectional Flow: The most defining characteristic of DC is its constant direction of flow. Current flows from positive to negative terminals and maintains this direction.
  • Constant Voltage/Current: In an ideal DC source like a battery, the voltage and current output are constant over time. Though in practical circuits, they might have minor fluctuations, the fundamental principle is a steady, non-alternating output.
  • Zero Frequency: Since DC does not alternate or change direction, its frequency is considered to be zero Hertz (0 Hz). This contrasts sharply with AC, which typically has frequencies like 50 Hz or 60 Hz.
  • Sources: Common sources of DC include batteries (chemical energy to electrical energy), solar cells (light energy to electrical energy), fuel cells, and rectifiers (devices that convert AC to DC).
  • Energy Storage: DC can be stored directly in batteries, which is a significant advantage for portable electronics and backup power systems.

Applications of Direct Current

DC is crucial for numerous applications, especially in modern electronics:

  • Portable Electronic Devices: Smartphones, laptops, tablets, and other battery-powered devices exclusively use DC.
  • Battery Charging: All types of batteries, from AA cells to electric vehicle batteries, are charged using DC.
  • Automotive Systems: Cars, trucks, and other vehicles rely on DC for their electrical systems, including starting, lighting, and onboard electronics.
  • Electroplating and Electrolysis: Industrial processes like electroplating (coating objects with a thin layer of metal) and electrolysis (chemical decomposition using electric current) require DC.
  • Photovoltaic (Solar) Systems: Solar panels generate DC, which is then often converted to AC for household use or stored in DC batteries.
  • High Voltage Direct Current (HVDC) Transmission: While AC is common for long-distance transmission, HVDC is gaining traction for very long distances and underwater cables due to lower power losses in certain scenarios.

DC vs. AC: A Quick Comparison

Feature Direct Current (DC) Alternating Current (AC)
Direction of Flow Unidirectional (constant) Bidirectional (reverses periodically)
Frequency 0 Hz 50 Hz or 60 Hz (common)
Voltage Transformation Difficult using transformers Easy using transformers
Storage Can be stored in batteries Cannot be stored directly
Applications Electronics, batteries, electroplating Household power, large motors, long-distance grid transmission

Quick Revision List

  • DC flows in one direction.
  • Ideal DC has constant voltage and current.
  • Frequency of DC is 0 Hz.
  • Batteries and solar cells are common DC sources.
  • Rectifiers convert AC to DC.
  • DC is essential for electronics, charging, and vehicles.
  • AC is better for long-distance voltage transformation.

Extra Practice Questions

  1. What is the primary characteristic that differentiates Direct Current from Alternating Current?
    1. Its higher voltage
    2. Its constant direction of flow
    3. Its ability to power large motors
    4. Its lower power loss
  2. Which of the following is NOT a common source of Direct Current?
    1. Solar panel
    2. Car battery
    3. Wall outlet
    4. Mobile phone charger (output)
  3. If a current has a frequency of 50 Hz, it is most likely a(n):
    1. Direct Current
    2. Pulsating DC
    3. Alternating Current
    4. Constant Current
  4. Why is DC generally used for electroplating?
    1. It helps in uniform deposition of metal.
    2. It is safer than AC.
    3. It generates more heat.
    4. It is easier to produce in large quantities.
  5. What role does a rectifier play in converting AC to DC?
    1. It increases the voltage.
    2. It filters out the current.
    3. It ensures the current flows in only one direction.
    4. It changes the frequency of the current.