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Chapter 15: Problem 1

Define back-emf, overpotential, and \(i R\) drop.

Short Answer

Expert verified
Back-emf opposes driving voltage in motors; overpotential is extra voltage for non-spontaneous reactions; \(iR\) drop is voltage loss in resistive circuits.

Step by step solution

01

Define Back-Emf

Back-electromotive force (back-emf) refers to the voltage generated by a motor or generator during operation that opposes the voltage driving the system. In electric motors, back-emf is produced when the armature moves through its magnetic field, and it works against the applied voltage, effectively limiting the current that can pass through the circuit.
02

Define Overpotential

Overpotential is the extra voltage necessary to drive a non-spontaneous electrochemical reaction at an electrode above the equilibrium potential. It accounts for losses due to kinetic barriers and is directly related to the reaction rate, influencing the energy efficiency of electrochemical cells.
03

Define iR Drop

The term \(iR\) drop, or ohmic drop, refers to the voltage loss across a resistive component in a circuit, calculated by the product of the current \(i\) through the component and its resistance \(R\). This drop represents energy dissipation as heat and is a fundamental concept in circuit analysis affecting power distribution and energy efficiency.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Back-Emf
Imagine you're riding a bike down a hill. As you pedal, your legs generate a force to keep the wheels turning. But as you coast, the movement of the wheels continues, generating a force that resists your pedaling effort. This is quite similar to how back-electromotive force, or back-emf, works in electric motors.

Back-emf occurs when an electric motor generates its own voltage during operation. This self-generated voltage acts in the opposite direction to the voltage supplied to the motor by the circuit. Consequently, it serves to reduce the overall current flowing through the system.

Key points to understand about back-emf include:
  • It is crucial for energy efficiency in motors, as it limits the current and prevents excessive power consumption.
  • The faster the motor spins, the greater the back-emf, as it depends on how quickly the motor's magnetic fields move.
  • It helps protect the motor from overheating by naturally regulating the current as motor speed changes.
Overpotential
In electrochemistry, overpotential is like an additional hurdle that an electrochemical reaction needs to overcome to proceed. If you think of a track race, overpotential is akin to extra hurdles placed in the path of the runners, requiring more effort to clear. It represents the additional energy needed to drive a reaction that doesn't happen on its own.

When discussing overpotential, consider the following:
  • It is essential for enabling non-spontaneous reactions, which are reactions that wouldn't occur without added electricity.
  • Overpotential is tied to kinetic barriers, meaning it influences how fast or slow a reaction can proceed.
  • Managing overpotential is key to improving the energy efficiency of devices like batteries and electrolyzers, making them last longer and work better.
Ohmic Drop
The concept of an iR drop, commonly known as ohmic drop, is very much like what happens when water flows through a narrow pipe. The resistance in the pipe causes some of the water pressure to be lost. Similarly, in electric circuits, the resistance encountered by the current causes a drop in voltage known as the iR or ohmic drop.

Here's what you need to know about ohmic drop:
  • This drop is determined by Ohm's Law, which states that the voltage drop (
  • It represents energy lost as heat due to resistance, impacting energy efficiency and power distribution.
  • Reducing ohmic drop is crucial for minimizing energy loss and ensuring that components work effectively and efficiently in a circuit.

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Most popular questions from this chapter

A solution contains about \(10^{-2} M \mathrm{Fe}^{3+}\) and \(10^{-5} M \mathrm{~Pb}^{2+}\). It is desired to analyze for the lead content polarographically. \(\mathrm{Fe}^{3+}\) is reduced to \(\mathrm{Fe}^{2+}\) at all potentials accessible with the DME up to \(-1.5 \mathrm{~V}\) versus \(\mathrm{SCE},\) and is reduced along with \(\mathrm{Fe}^{2+}\) to the metal at potentials more negative than \(-1.5 \mathrm{~V}\). \(\mathrm{Pb}^{2+}\) is reduced at \(-0.4 \mathrm{~V}\). Suggest a scheme for measuring the lead polarographically.

Give two reasons for using a supporting electrolyte in voltammetry.

Define half-wave potential, depolarizer, DME, residual current, and voltammetry.

What is the function of an electrocatalyst in a chemically modified electrode?

What are the advantages of an ultramicroelectrode?
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