4A5 Electrical Potential Flashcards

Explain the sources and processes required to generate electrical potential and electromotive force. (58 cards)

1
Q

Define:

Electrical potential

A

It is the potential energy per unit charge at a point in an electric field.

Electrical potential is measured in volts (V).

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2
Q

Fill in the blank:

A ______ converts chemical energy into electrical energy.

A

battery

Batteries store chemical energy for direct current (DC) applications.

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3
Q

Define:

Electrode

A

Conductor that allows electrical current to enter or leave a device or medium, such as a battery or electrochemical cell.

It can be either an anode or a cathode.

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4
Q

What is the purpose of a battery electrolyte?

A

It allows the flow of ions between electrodes to sustain chemical reactions.

Common electrolytes include sulfuric acid in lead-acid batteries.

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5
Q

What is a redox process?

A

It involves two simultaneous reactions: oxidation, where a substance loses electrons, and reduction, where a substance gains electrons.

This process is crucial for chemical reactions, energy storage in batteries, and electrochemical applications.

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6
Q

Fill in the blank:

In a battery, the anode electrode is where _______ occurs.

A

oxidation

The anode releases electrons during oxidation.

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7
Q

What is the role of the cathode in a battery?

A

It is the electrode where reduction occurs, and electrons flow toward it during discharge.

In rechargeable batteries, the cathode and anode switch roles during charging.

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8
Q

Fill in the blank:

In a zinc-carbon battery, zinc serves as the _______, undergoing oxidation by releasing electrons.

A

anode

The zinc atoms lose electrons, forming zinc ions (Zn²⁺) and providing current flow.

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9
Q

What is a lead-acid battery?

A

A rechargeable battery that uses lead and lead dioxide plates submerged in sulfuric acid.

Common in cars.

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10
Q

Define:

Dry cell

A

Type of battery with a paste electrolyte instead of liquid.

Alkaline batteries are common examples.

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11
Q

Why are alkaline batteries preferred for portable electronics?

A
  • Lightweight
  • Stable voltage
  • Long shelf life

They are more environmentally friendly than older battery types.

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12
Q

What happens when you connect two batteries in parallel?

A

The total voltage remains the same, but the current capacity increases.

Parallel connections are ideal for extending battery life.

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13
Q

How would you connect batteries to increase electrical potential in a circuit?

A

Connect them in series.

In series, the voltages of the batteries are summed.

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14
Q

How does temperature impact battery performance?

A

High temperatures shorten battery life, while low temperatures reduce performance and efficiency.

Lithium-ion batteries are sensitive to temperature changes.

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15
Q

Describe how a flashlight battery provides electrical potential.

A

By converting chemical energy into electrical energy to power the bulb.

Flashlights often use dry cell batteries.

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16
Q

What is the purpose of a salt bridge in a battery?

A

It maintains electrical neutrality by allowing the flow of ions between the two half-cells.

It prevents the accumulation of charge that would stop the reaction.

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17
Q

Fill in the blank:

In a rechargeable battery, energy is supplied to _______ the chemical reactions, restoring the battery’s capacity.

A

reverse

This reversal restores the original chemical composition, allowing the battery to store and release energy again.

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18
Q

What happens when a battery’s chemical reactants are fully consumed?

A

The battery stops generating electrical energy, as no further redox reactions can occur.

This is why disposable batteries eventually lose their charge and must be replaced.

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19
Q

True or false:

Photocells generate electrical potential by converting heat into electricity.

A

False

Photocells convert light, not heat, into electricity.

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20
Q

What are the main components of a photocell?

A
  • Semiconductor layer
  • Electrodes
  • Encapsulation layer
  • Anti-reflective coating

Photocells are also known as photovoltaic cells.

Semiconductor layer: Absorbs light and generates electron-hole pairs.

Electrodes: Collect the generated current.

Encapsulation layer: Protects the cell from environmental damage.

Anti-reflective coating: Increases light absorption efficiency.

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21
Q

Why can’t a solar panel generate electricity in the dark?

A

Photocells require light to release electrons and produce current.

Solar panels are ineffective without light sources.

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22
Q

Describe a situation where a photocell could be more effective than a battery.

A

In outdoor applications with abundant sunlight, such as solar garden lights.

Photocells are renewable but weather-dependent.

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23
Q

How does increasing the surface area of a photocell affect its efficiency?

A

It allows more light to be captured, generating higher electrical potential.

Surface design is critical for solar panel efficiency.

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24
Q

Define:

Electric generator

A

A device that converts mechanical energy into electrical energy through electromagnetic induction.

Generators are essential for producing electricity in both large power grids and portable applications.

25
How does **electromagnetic induction** work in generators?
Generators produce electricity by **moving a conductor through a magnetic field,** inducing an electromotive force (EMF) according to Faraday's Law. ## Footnote The magnitude of EMF depends on the speed of motion, strength of the magnetic field, and number of coil turns.
26
Why are **generators** important in **power plants**?
They provide the **main source of electrical potential** for power distribution. ## Footnote Turbines, powered by steam, water, or wind, rotate generator coils to induce electricity.
27
List the key **components** of a **generator** and their functions.
* **Rotor**: Rotates to produce a magnetic field. * **Stator**: Contains the coil where EMF is induced. * **Brushes**: Maintain electrical contact with the rotating parts. * **Slip rings**: Transfer current between rotor and external circuit. ## Footnote Generators convert mechanical energy into electrical energy.
28
Only **mechanical energy** sources can drive a **generator**.
False ## Footnote Generators can also use thermal and hydraulic energy.
29
How can **generators** be classified?
* The **type of current** they produce: AC (alternating current) or DC (direct current). * The **energy source** used, such as hydroelectric, wind, or solar energy. ## Footnote Classification helps identify the most suitable generator for specific energy needs.
30
List different types of **generators** based on their **energy source**.
* Hydroelectric Generator: Powered by water flow. * Wind Generator: Converts wind energy. * Solar Thermal Generator: Uses solar heat. * Fuel-Based Generator: Relies on fossil fuels. ## Footnote Each type of generator is optimized for specific environmental or economic conditions.
31
How would a **faulty battery** affect the electrical potential of a circuit?
It would **reduce or completely stop** the flow of current. ## Footnote Battery degradation reduces charge efficiency.
32
# True or false: Generators require **brushes** to maintain electrical contact.
True ## Footnote Brushes transfer current from the rotating coil to the circuit.
33
# Fill in the blank: **Generators** typically produce \_\_\_\_\_\_ current.
alternating (AC) ## Footnote AC can be transmitted over long distances with less loss.
34
# Fill in the blank: **EMF** is often described as the \_\_\_\_\_\_ of a **power source**.
voltage ## Footnote EMF represents the maximum potential difference across a power source.
35
# True or false: EMF always results in a **current flow** in a circuit.
False ## Footnote Current flows only when there is a complete circuit and a load connected.
36
What is the **unit** of electromotive force (EMF)
Volts (V) ## Footnote It shares the same unit as potential difference.
37
What is the relationship between **EMF** and **internal resistance**?
EMF is the **sum of the terminal voltage** and the voltage drop across the internal resistance. ## Footnote Internal resistance reduces the usable voltage in a circuit.
38
# Fill in the blank: **EMF** in a **generator** depends on the strength of the \_\_\_\_\_\_\_ \_\_\_\_\_\_ and the speed of rotation.
magnetic field ## Footnote Stronger magnetic fields and faster rotations generate higher EMF.
39
How can **EMF** be increased in a generator?
* Increase the speed of rotation. * Use stronger magnets. ## Footnote Coil design can also affect EMF production.
40
# True or false: The **magnitude of EMF** is directly proportional to the **number of turns in a coil**.
True ## Footnote According to Faraday’s Law, EMF is proportional to the rate of change of magnetic flux times the number of turns.
41
How is **electromotive force (EMF)** calculated?
EMF=V+Ir ## Footnote where V is the terminal voltage, I is the current, and r is the internal resistance of the source.
42
How is **EMF** different from **potential difference**?
* EMF is the **total energy** provided by a source. * Potential difference is the **energy used between two points** in a circuit. ## Footnote Internal resistance reduces the effective voltage available.
43
A battery has an EMF of **12V** and an internal resistance of **1Ω**. What is the terminal voltage when the current is **2A**?
10V ## Footnote Terminal voltage = EMF - (Current × Internal Resistance).
44
# Fill in the blank: **EMF** is represented by the **symbol** \_\_\_\_\_\_.
ε (epsilon) ## Footnote EMF is often denoted by ε in equations.
45
# Fill in the blank: The \_\_\_\_\_\_ \_\_\_\_\_ of a power source generates **EMF**.
chemical reaction | (or magnetic induction) ## Footnote Batteries use chemical reactions; generators use electromagnetic induction.
46
# True or false: **EMF** can be generated without any **external input**.
False ## Footnote EMF always requires a source of energy, such as chemical, solar, or mechanical energy.
47
# Define: Back EMF
EMF induced in a motor that **opposes the applied voltage**. ## Footnote Back EMF occurs due to the motor's rotation.
48
# Fill in the blank: **Back EMF** is essential for controlling the \_\_\_\_\_\_ of an electric motor.
speed ## Footnote Higher back EMF reduces the net voltage driving the motor.
49
What does **Faraday’s Law** of Electromagnetic Induction state?
The induced **electromotive force (EMF)** in a closed circuit is directly proportional to the rate of change of magnetic flux through the circuit. ## Footnote EMF= - ΦB/dt, where ΦB is the magnetic flux, and the negative sign follows Lenz’s Law, indicating the direction of the induced EMF opposes the change in flux.
50
Why does **EMF decrease** as a **battery discharges**?
The **chemical energy** available for conversion decreases, increasing **internal resistance**. ## Footnote Battery aging also contributes to EMF reduction.
51
What is the role of **EMF** in **solar cells**?
EMF is generated when photons displace electrons, creating potential difference. ## Footnote Solar cells convert light directly into electrical energy.
52
# True or false: A **dead battery** has zero EMF.
False ## Footnote It may still have a small EMF but insufficient to provide current.
53
What is the source of **EMF** in a **thermocouple**?
Temperature difference between two dissimilar metals. ## Footnote Thermocouples are used in temperature sensors.
54
# True or false: **EMF** can only be generated by **batteries**.
False ## Footnote EMF can come from batteries, generators, solar cells, and more.
55
How does a **fuel cell** maintain a **stable EMF**?
By continuously supplying fuel and maintaining proper chemical conditions. ## Footnote Fuel cells are efficient but require constant fuel input.
56
What happens when **internal resistance** in a **battery** becomes too high?
The terminal voltage drops, reducing circuit performance. ## Footnote High internal resistance indicates battery degradation.
57
How does a **rechargeable battery** maintain its **EMF** after multiple cycles?
It relies on **reversible chemical reactions** during charging and discharging. ## Footnote Over time, efficiency decreases.
58
Why is **EMF** important in understanding **power systems**?
It determines the maximum voltage available for work in a circuit. ## Footnote Efficient power generation relies on maintaining consistent EMF.