4A5 Electrical Potential

Question 1

Define:

Electrical potential

Answer 1

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

Electrical potential is measured in volts (V).

Question 2

Fill in the blank:

A ______ converts chemical energy into electrical energy.

Answer 2

battery

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

Question 3

Define:

Electrode

Answer 3

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.

Question 4

What is the purpose of a battery electrolyte?

Answer 4

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

Common electrolytes include sulfuric acid in lead-acid batteries.

Question 5

What is a redox process?

Answer 5

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.

Question 6

Fill in the blank:

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

Answer 6

oxidation

The anode releases electrons during oxidation.

Question 7

What is the role of the cathode in a battery?

Answer 7

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.

Question 8

Fill in the blank:

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

Answer 8

anode

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

Question 9

What is a lead-acid battery?

Answer 9

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

Common in cars.

Question 10

Define:

Dry cell

Answer 10

Type of battery with a paste electrolyte instead of liquid.

Alkaline batteries are common examples.

Question 11

Why are alkaline batteries preferred for portable electronics?

Answer 11

• Lightweight
• Stable voltage
• Long shelf life

They are more environmentally friendly than older battery types.

Question 12

What happens when you connect two batteries in parallel?

Answer 12

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

Parallel connections are ideal for extending battery life.

Question 13

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

Answer 13

Connect them in series.

In series, the voltages of the batteries are summed.

Question 14

How does temperature impact battery performance?

Answer 14

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

Lithium-ion batteries are sensitive to temperature changes.

Question 15

Describe how a flashlight battery provides electrical potential.

Answer 15

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

Flashlights often use dry cell batteries.

Question 16

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

Answer 16

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.

Question 17

Fill in the blank:

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

Answer 17

reverse

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

Question 18

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

Answer 18

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.

Question 19

True or false:

Photocells generate electrical potential by converting heat into electricity.

Answer 19

False

Photocells convert light, not heat, into electricity.

Question 20

What are the main components of a photocell?

Answer 20

• 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.

Question 21

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

Answer 21

Photocells require light to release electrons and produce current.

Solar panels are ineffective without light sources.

Question 22

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

Answer 22

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

Photocells are renewable but weather-dependent.

Question 23

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

Answer 23

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

Surface design is critical for solar panel efficiency.

Question 24

Define:

Electric generator

Answer 24

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.

Question 25

How does **electromagnetic induction** work in generators?

Answer 25

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.

Question 26

Why are **generators** important in **power plants**?

Answer 26

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.

Question 27

List the key **components** of a **generator** and their functions.

Answer 27

* **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.

Question 28

Only **mechanical energy** sources can drive a **generator**.

Answer 28

False ## Footnote Generators can also use thermal and hydraulic energy.

Question 29

How can **generators** be classified?

Answer 29

* 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.

Question 30

List different types of **generators** based on their **energy source**.

Answer 30

* 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.

Question 31

How would a **faulty battery** affect the electrical potential of a circuit?

Answer 31

It would **reduce or completely stop** the flow of current. ## Footnote Battery degradation reduces charge efficiency.

Question 32

# True or false: Generators require **brushes** to maintain electrical contact.

Answer 32

True ## Footnote Brushes transfer current from the rotating coil to the circuit.

Question 33

# Fill in the blank: **Generators** typically produce \_\_\_\_\_\_ current.

Answer 33

alternating (AC) ## Footnote AC can be transmitted over long distances with less loss.

Question 34

# Fill in the blank: **EMF** is often described as the \_\_\_\_\_\_ of a **power source**.

Answer 34

voltage ## Footnote EMF represents the maximum potential difference across a power source.

Question 35

# True or false: EMF always results in a **current flow** in a circuit.

Answer 35

False ## Footnote Current flows only when there is a complete circuit and a load connected.

Question 36

What is the **unit** of electromotive force (EMF)

Answer 36

Volts (V) ## Footnote It shares the same unit as potential difference.

Question 37

What is the relationship between **EMF** and **internal resistance**?

Answer 37

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.

Question 38

# Fill in the blank: **EMF** in a **generator** depends on the strength of the \_\_\_\_\_\_\_ \_\_\_\_\_\_ and the speed of rotation.

Answer 38

magnetic field ## Footnote Stronger magnetic fields and faster rotations generate higher EMF.

Question 39

How can **EMF** be increased in a generator?

Answer 39

* Increase the speed of rotation. * Use stronger magnets. ## Footnote Coil design can also affect EMF production.

Question 40

# True or false: The **magnitude of EMF** is directly proportional to the **number of turns in a coil**.

Answer 40

True ## Footnote According to Faraday’s Law, EMF is proportional to the rate of change of magnetic flux times the number of turns.

Question 41

How is **electromotive force (EMF)** calculated?

Answer 41

EMF=V+Ir ## Footnote where V is the terminal voltage, I is the current, and r is the internal resistance of the source.

Question 42

How is **EMF** different from **potential difference**?

Answer 42

* 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.

Question 43

A battery has an EMF of **12V** and an internal resistance of **1Ω**. What is the terminal voltage when the current is **2A**?

Answer 43

10V ## Footnote Terminal voltage = EMF - (Current × Internal Resistance).

Question 44

# Fill in the blank: **EMF** is represented by the **symbol** \_\_\_\_\_\_.

Answer 44

ε (epsilon) ## Footnote EMF is often denoted by ε in equations.

Question 45

# Fill in the blank: The \_\_\_\_\_\_ \_\_\_\_\_ of a power source generates **EMF**.

Answer 45

chemical reaction | (or magnetic induction) ## Footnote Batteries use chemical reactions; generators use electromagnetic induction.

Question 46

# True or false: **EMF** can be generated without any **external input**.

Answer 46

False ## Footnote EMF always requires a source of energy, such as chemical, solar, or mechanical energy.

Question 47

# Define: Back EMF

Answer 47

EMF induced in a motor that **opposes the applied voltage**. ## Footnote Back EMF occurs due to the motor's rotation.

Question 48

# Fill in the blank: **Back EMF** is essential for controlling the \_\_\_\_\_\_ of an electric motor.

Answer 48

speed ## Footnote Higher back EMF reduces the net voltage driving the motor.

Question 49

What does **Faraday’s Law** of Electromagnetic Induction state?

Answer 49

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.

Question 50

Why does **EMF decrease** as a **battery discharges**?

Answer 50

The **chemical energy** available for conversion decreases, increasing **internal resistance**. ## Footnote Battery aging also contributes to EMF reduction.

Question 51

What is the role of **EMF** in **solar cells**?

Answer 51

EMF is generated when photons displace electrons, creating potential difference. ## Footnote Solar cells convert light directly into electrical energy.

Question 52

# True or false: A **dead battery** has zero EMF.

Answer 52

False ## Footnote It may still have a small EMF but insufficient to provide current.

Question 53

What is the source of **EMF** in a **thermocouple**?

Answer 53

Temperature difference between two dissimilar metals. ## Footnote Thermocouples are used in temperature sensors.

Question 54

# True or false: **EMF** can only be generated by **batteries**.

Answer 54

False ## Footnote EMF can come from batteries, generators, solar cells, and more.

Question 55

How does a **fuel cell** maintain a **stable EMF**?

Answer 55

By continuously supplying fuel and maintaining proper chemical conditions. ## Footnote Fuel cells are efficient but require constant fuel input.

Question 56

What happens when **internal resistance** in a **battery** becomes too high?

Answer 56

The terminal voltage drops, reducing circuit performance. ## Footnote High internal resistance indicates battery degradation.

Question 57

How does a **rechargeable battery** maintain its **EMF** after multiple cycles?

Answer 57

It relies on **reversible chemical reactions** during charging and discharging. ## Footnote Over time, efficiency decreases.

Question 58

Why is **EMF** important in understanding **power systems**?

Answer 58

It determines the maximum voltage available for work in a circuit. ## Footnote Efficient power generation relies on maintaining consistent EMF.