Difference Between AC & DC | Physics for EmSAT Achieve PDF Download

• Overview of Electric Current
• Introduction to Alternating Current (AC) and Direct Current (DC)
• Understanding Alternating Current (AC)
• Definition of AC
• Characteristics of AC
• Application of AC in Household and Industrial Settings
• Example of AC Usage: Electric Motors
• Understanding Direct Current (DC)
• Definition of DC
• Characteristics of DC
• Comparison with AC
• Example of DC Usage: Battery-Powered Devices
• Differences Between AC and DC
• Direction of Electron Flow
• Steadiness of Current
• Usages and Applications
• Efficiency and Transmission
• Frequency and Waveform of Alternating Current
• Sine Wave Representation
• Measurement in Hertz (Hz)
• Significance in Power Generation
• Advantages in Long-Distance Transmission
• Practical Applications of AC
• Household Appliances
• Powering Electric Motors
• Industrial Machinery
• Transportation Systems

Direct Current (DC) vs. Alternating Current (AC)

• Definition of DC and AC:
  • Direct Current (DC) flows steadily in a single direction without periodic changes. It is commonly used to power electrical devices and charge batteries.
  • Alternating Current (AC) changes its flow direction periodically and is used for transferring electricity over long distances.
• Examples of DC and AC applications:
  • DC is utilized in devices like mobile phone batteries, flashlights, flat-screen televisions, and electric vehicles.
  • AC powers appliances such as cellphones, electric vehicles, flashlights, and flat-screen TVs.
• Differences between AC and DC:
  • AC can be transmitted over longer distances with minimal energy loss, unlike DC which loses power over long distances.
  • AC changes its current direction due to rotating magnets, while DC maintains a steady flow in one direction.
  • The frequency of AC varies by country but is typically around 50-60 Hz, whereas DC has zero frequency.
  • Electrons in AC oscillate back and forth, while electrons in DC flow consistently in one direction.

Why AC Can't Be Stored in Batteries Instead of DC?

• Batteries store electrical energy in the form of chemical energy, not directly.
• When AC is connected to a battery, the changing polarity cancels out the energy supply, potentially damaging the battery.

Advantages of AC Over DC

• AC is more cost-effective and easier to generate compared to DC.
• AC can be transmitted across long distances with minimal energy loss, unlike DC.
• Power loss during AC transmission is lower than that during DC transmission.

Why AC Voltage is Preferred Over DC Voltage?

• AC voltage is preferred due to its cost-effectiveness and ease of generation.
• It can be transmitted efficiently across long distances with minimal energy loss.

Test Questions

1. Why can't AC be stored directly in batteries? Explain the potential damage it can cause.
2. List and explain three advantages of AC over DC.
3. Discuss why the use of AC voltage is preferred over DC voltage, providing reasons for its efficiency.

Advantages of AC Voltage over DC Voltage:

• The loss of energy in AC transmission is lower than in DC transmission, making it more suitable for long-distance power transmission.
• AC voltage allows for easy stepping up and stepping down of voltage levels based on requirements.

Understanding Wattless Current:

Wattless current refers to the current in an AC circuit where the average power consumption is zero. This phenomenon occurs in situations where reactive power is present without real power being consumed.

Power Factor at Resonance:

At resonance, the power factor in a circuit reaches its maximum value of 1. This indicates that the circuit is operating at its most efficient state, with minimal losses.

Reasons for Energy Loss in Transformers:

• Hysteresis: Energy loss due to the magnetic properties of the core material.
• Eddy Current Loss: Energy dissipation caused by induced currents circulating within the transformer's core.
• Leakage of Flux: Energy loss resulting from magnetic flux not linking both primary and secondary windings effectively.

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When discussing alternating current (AC), the polarity changes due to the interaction between a magnet and a coil of wire in an electric generator. As the wire rotates within the magnetic field, the varying strength of the field induces a force, propelling electric charges along the wire. Initially, this force moves charges in one direction. However, as the loop completes a 180-degree rotation, the force reverses, causing the current to flow in the opposite direction. This reversal in force and current direction occurs every 180 degrees of rotation.

In India, the decision to adopt a 50Hz frequency for power supply, as opposed to the 60Hz frequency used in the US, is influenced by various factors. These include environmental considerations, power generation costs, and losses related to eddy currents and hysteresis. The higher average annual temperature in India and the associated power generation expenses make the 50Hz frequency a more suitable choice. Additionally, higher frequencies lead to increased eddy current and hysteresis losses, resulting in greater power loss.

Understanding Alternating Current Generation

• Basic Principle of Electric Generator:
  • When a coil of wire rotates within a magnetic field in an electric generator, it induces an alternating current.
• Function of the Magnetic Field:
  • The magnet and rotating wire coil interact to create changing magnetic strengths that induce a force in the wire.
• Generation of Electric Charges:
  • The force generated in the wire initially drives electric charges in a specific direction.
• Current Reversal Mechanism:
  • As the wire loop completes a 180-degree rotation, the force reverses, leading to an electric current in the opposite direction.
• Changing Polarity:
  • With every 180-degree rotation of the loop, the direction of the force changes, altering the polarity of the current.

Why is the Power Supply Frequency 50Hz in India and Not 60Hz?

• Environmental Factors: India's higher average annual temperature compared to the US is a key reason why the power supply frequency is set at 50 Hz. Higher temperatures can affect the efficiency of power transmission and usage.
• Power Generation Costs: Generating power at a higher frequency, such as 60 Hz, is more expensive. This cost consideration plays a significant role in determining the optimal frequency for power supply in a country.
• Eddy Current Losses: As the frequency of power supply increases, so do eddy current and hysteresis losses. These losses result in decreased efficiency and increased power wastage. By maintaining a frequency of 50 Hz, India can mitigate these losses to a certain extent.

• Environmental factors play a crucial role in power generation.

• Generating power at higher frequencies can be costly.

• As the frequency increases, both eddy current and hysteresis losses also increase.
• This results in a corresponding increase in power loss.

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