Electricity

Electrostatic Phenomena: Understanding Charging and Discharging

1. Electrostatic phenomena refer to the behaviors and effects of electric charges

at rest. These effects can be easily observed in everyday life, such as when a
balloon sticks to a wall after being rubbed against clothes or when it deflects a
stream of water from a tap.
2. Electrostatic Phenomena: Observable effects caused by electric charges.
3. Charging: The process of adding or removing electric charge on an object.
4. Discharging: The process of removing electric charge from an object, often
through grounding.

Charging a Balloon

1. When you rub a balloon against your clothes, electrons are transferred from
your clothes to the balloon. This transfer of electrons charges the balloon
negatively. Because of this negative charge, the balloon can:

• Stick to a Wall: The balloon induces a positive charge on the surface of the wall,
causing attraction.
• Deflect a Stream of Water: The charged balloon attracts the polar molecules of
water, causing the stream to bend.
• Pick Up Small Pieces of Paper: The negatively charged balloon induces a positive
charge on the pieces of paper, causing them to be attracted to the balloon.

Charging and Discharging Experiment

Adam rubs different rods with a cloth and observes their interactions:

1. Polythene Rods:
o When rubbed with a cloth, the polythene rod becomes negatively
charged (gains electrons).

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 o Two negatively charged polythene rods repel each other because like
charges repel.
2. Polythene and Perspex Rods:
o When Adam rubs a Perspex rod with a cloth, it becomes positively
charged (loses electrons).
o A negatively charged polythene rod and a positively charged Perspex
rod attract each other because unlike charges attract.

Why Do Objects Become Charged?

1. Objects become charged due to the transfer of electrons:

• Negative Charge (-): An object gains extra electrons.

• Positive Charge (+): An object loses electrons.

Types of Electric Charge

• Positive Charge (+)

• Negative Charge (-)

Principles of Electric Charges

• Like Charges Repel: Positive repels positive, and negative repels negative.
• Unlike Charges Attract: Positive attracts negative.

Objectives Recap

1. Know the Types of Charge:

o Positive (+) and Negative (-).
2. Explain Why Things Become Charged:
o Due to the transfer of electrons through friction or contact, causing an
imbalance in the number of protons and electrons.
3. Explain the Difference Between Conductors and Insulators:
o Conductors allow electric charge to move freely, while insulators do not.

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 4. Example: Rubbing a balloon on your hair.

• When you rub a balloon on your hair, electrons transfer from your hair to the
balloon, making the balloon negatively charged.
• Your hair, now positively charged, stands up because the individual strands of
hair repel each other.

Where Does the Charge Come From?

Structure of an Atom

• Atoms are the building blocks of all materials.

• Atoms consist of three types of particles:
o Protons: Positively charged.
o Neutrons: No charge (neutral).
o Electrons: Negatively charged.
• Nucleus: Center of the atom containing protons and neutrons.
• Electrons: Orbit the nucleus in different energy levels or shells.

Neutral Atoms

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 • In a neutral atom, the number of protons equals the number of electrons.
• The positive and negative charges cancel out, resulting in no net charge.

Charging by Friction

• When you rub a material (like a polythene rod) with a cloth, electrons are
transferred between the materials.
o Polythene Rod: Gains electrons from the cloth, becoming negatively
charged.
o Cloth: Loses electrons, becoming positively charged.
• When you rub a Perspex rod:
o Perspex Rod: Loses electrons to the cloth, becoming positively charged.
o Cloth: Gains electrons, becoming negatively charged.

Conservation of Charge

• Charge cannot be created or destroyed, only transferred.

• The total amount of charge remains constant in an isolated system.

Conductors vs. Insulators

• Conductors: Materials that allow electrons to move freely (e.g., metals).

o Example: If you charge a metal rod, the electrons will move through the
metal and can be transferred to your hand, then to the ground (earth).
• Insulators: Materials that do not allow electrons to move freely (e.g., plastic,
rubber).
o Example: A charged polythene or Perspex rod retains the charge
because the electrons cannot move through the material.

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Static Electricity

• Static: Means stationary or standing still.

• Electrostatic phenomena: Observable effects caused by stationary electric
charges (e.g., the attraction and repulsion of charged rods).

Example 1: Static Cling in Clothes

Scenario: After taking clothes out of the dryer, you may notice that some items stick
together.

Explanation:

• Friction in the Dryer: As clothes tumble and rub against each other in the dryer,
electrons are transferred between different pieces of clothing.
• Charge Imbalance: Some clothes become negatively charged while others
become positively charged.
• Attraction and Repulsion: Oppositely charged clothes attract each other,
causing them to stick together (static cling).

Example 2: Dust and Small Particles Clinging to Surfaces

Scenario: Dust particles sticking to a TV screen or computer monitor.

Explanation:

• Static Charge on Screen: Electronic screens can build up a static charge when
they are turned on and off, due to the movement of electrons in the display.
• Attraction of Dust: Dust and small particles in the air, which may be neutrally
charged or carry a small positive or negative charge, are attracted to the screen
because of the static charge.
• Accumulation: This causes dust to cling to the screen until it is cleaned off.

Example 3: Walking on a Carpet and Getting a Shock

Scenario: Walking across a carpeted floor and then touching a metal doorknob,
resulting in a small electric shock.

Explanation:

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 • Friction with the Carpet: As you walk, electrons are transferred between your
shoes and the carpet, causing your body to accumulate a static charge.
• Static Charge Build-up: Your body becomes either positively or negatively
charged depending on the direction of electron transfer.
• Discharge: When you touch a metal doorknob, the charge quickly moves from
your body to the doorknob (or vice versa), resulting in a small shock as the
electrons move to neutralize the charge imbalance.

Dangers of Electrostatic Phenomena

Electrostatic phenomena, while fascinating and often harmless in everyday situations,

can also pose significant dangers. One of the most dramatic and dangerous examples
of electrostatic phenomena is lightning.

1. Electrostatic Phenomena: Observable effects caused by electric charges at rest,

which can sometimes result in dangerous sparks and electric shocks.
2. Electric Current: The movement of electric charge, which can occur in the form
of a spark.

Lightning

• Formation: During a thunderstorm, air currents within a cloud cause regions to

become positively and negatively charged.
• Discharge: When enough charge builds up, the air between these regions can
conduct electricity, resulting in a massive spark, or lightning.
• Path to Earth: Lightning often travels from the negatively charged region of a
cloud to the ground, creating a visible and audible phenomenon.

Sparks and Current

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 • Charge Build-up: Friction can cause significant charge accumulation, leading to
a spark.
• Spark Characteristics: A spark involves charge moving through the air, heating
it up, which produces light and sound.
• Electric Current: The moving charge in a spark is an electric current.

Dangers of Lightning

• Physical Harm: Lightning can cause severe injuries or death if it strikes a person.
o Burns: The intense heat of the electric current can cause burns.
o Bone Damage: The force of the lightning strike can break bones.
o Heart Interference: The electric current can disrupt the heart’s rhythm
or stop it entirely, leading to cardiac arrest.

Electric Shocks in Other Contexts

• Defibrillation: In a controlled medical environment, a strong electric current can

be used to restart a stopped heart. This is done using a defibrillator, which
delivers a measured electric shock to the patient’s heart.

Reducing the Risk of Damage from Electrostatic Phenomena

1. Lightning Protection Systems

• Lightning Rods: These are metal rods placed on buildings to safely direct the
charge from a lightning strike to the ground, preventing damage to the
structure and reducing the risk of fire.

• Grounding Systems: Ensuring that buildings and electrical systems are

properly grounded helps to safely dissipate electric charge into the earth.

2. Personal Safety Measures

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 • During Thunderstorms: Avoid open areas, tall objects, and conductive materials
(like metal fences) which can attract lightning.
• Safe Shelters: Stay indoors or in a car during a thunderstorm. Both provide
better protection from lightning strikes.

3. Workplace Safety

• Electrostatic Discharge (ESD) Precautions: In environments where static

electricity can damage electronic components, workers use ESD wrist straps,
mats, and other grounding techniques to prevent charge build-up.

• Proper Clothing and Footwear: Wearing clothes and shoes made of materials
that do not generate static electricity can help reduce the risk of sparks.

Objectives Recap

1. Describe How Electrostatic Phenomena Can Be Dangerous:

o Lightning can cause burns, break bones, or stop the heart.
o Uncontrolled electric shocks can cause severe injuries or death.
2. Explain How the Risk of Damage from Electrostatic Phenomena Can Be
Reduced:
o Use lightning rods and grounding systems to protect structures.
o Avoid exposure during thunderstorms by staying indoors.
o Implement ESD precautions in workplaces dealing with sensitive
electronics.

Reducing the Risk of Electrostatic Phenomena

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Electrostatic phenomena can pose significant risks, especially during thunderstorms, in
fuel handling, and in the electronics industry. Understanding how to reduce these risks
is crucial for safety.

1. Risk: The combination of the probability of an event occurring and the

consequences if it does.
2. Earthing/Grounding: Connecting an object to the Earth with a conductor to
safely dissipate charge and reduce the risk of sparks or damage.

Reducing Risk During Thunderstorms

Lightning Conductors

• Lightning Conductors: Thick strips of metal, usually copper, running down

buildings and attached to copper plates buried underground.
• Function: Directs the electric charge from a lightning strike safely into the
ground, preventing damage to the building.

Example:

• High-rise buildings and towers often have lightning conductors to protect them
from lightning strikes. When lightning hits the building, the conductor provides
a path for the electrons to flow to the ground, reducing the risk of structural
damage.

Personal Safety

• Avoid Trees: Trees are likely to be struck by lightning, so sheltering under them
during a thunderstorm is dangerous.
• Seek Safe Shelter: Stay indoors or in a vehicle to avoid being struck by lightning.

Reducing Risk in Fuel Handling

Fuel Pipes

• Risk: The friction of fuel moving through pipes can cause a charge to build up,
leading to potential sparks and fire hazards.
• Solution: Earthing the fuel pipes by attaching a metal wire to them. This allows
any built-up charge to flow safely to the ground, reducing the risk of a spark and
subsequent explosion.

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Example:

• When refueling airplanes, the fuel nozzle and the plane are earthed to prevent
static electricity from causing a spark.

Reducing Risk in Electronics

Electrostatic Discharge (ESD) Precautions

• Risk: Static electricity can damage delicate electronic components.

• Solution: Engineers wear special wristbands connected to a metal wire that
goes to the ground. This allows any charge build-up to flow safely to the ground,
protecting the components.

Example:

• In a factory assembling electronic devices like TVs or smartphones, workers use

ESD wristbands to prevent static discharge from damaging the products.

Everyday Electrostatics

Common Experiences

• Car Doors: A small shock when touching a car door can occur because the car
has become charged by friction while moving.
• Clothing: Sparks and crackling sounds when removing clothing can happen due
to the buildup of static electricity.

Objectives Recap

1. Describe How Electrostatic Phenomena Can Be Dangerous:

o Lightning can cause severe damage or injuries.
o Sparks in fuel handling can lead to fires or explosions.
o Static discharge can damage electronic components.
2. Explain How the Risk of Damage from Electrostatic Phenomena Can Be
Reduced:
o Use lightning conductors to protect buildings.
o Earth fuel pipes to prevent sparks during refueling.
o Use ESD precautions to protect delicate electronics.

Digital Sensors: Touch Screens and Digital Cameras

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Digital sensors are integral to the functioning of modern devices like mobile phones
and digital cameras. Understanding how touch screens and digital cameras work can
enhance our appreciation of the technology we use daily.

Touch Screens

How Touch Screens Work

Touch screens rely on the principle of capacitance to detect the position of your touch.

Capacitor Basics

• Capacitor: An electronic component that stores electric charge.

• Structure: Consists of two metal plates separated by an insulating material
called a dielectric.
• Charging: When connected to a battery, electrons are pulled from one plate
and pushed onto the other, creating a potential difference.
• Disconnection: Once the battery is disconnected, the stored charge remains
because the electrons cannot move through the dielectric.

Capacitive Touch Screen Operation

• Capacitive Touch Screen: Functions like a capacitor.

o First Plate: Incorporated into the screen.
o Second Plate: Your finger.
• Sensing Circuit: Detects changes in capacitance when your finger touches the
screen.
o Detection: The circuit measures the capacitance at different points on
the screen to determine where your finger is.

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 o Functionality: This allows the device to detect which part of the screen
is being touched, enabling actions such as dialing a phone number or
interacting with an app.

Advanced Touch Screen Features

• Multi-touch: Can detect multiple points of contact simultaneously, enabling

gestures like pinching to zoom or swiping to scroll.
• Glove Compatibility: Some advanced touch screens are designed to work even
when the user is wearing gloves.
• Alternative Technologies: While many touch screens use capacitive technology,
some use other methods like resistive or infrared sensing.

Example: Dialing a Number on a Touch Screen Phone

• Touching a Number: When you touch a number on the screen, your finger acts
as one plate of a capacitor.
• Detection: The sensing circuit detects the change in capacitance at the location
of your touch.
• Action: The phone interprets this input and dials the corresponding number.

Digital Cameras

How Digital Cameras Work

Digital cameras use a charge-coupled device (CCD) to convert light into electronic
signals.

Charge-Coupled Device (CCD)

• CCD Structure: A grid of components that function like capacitors.

• Light Detection: When light (radiation) hits each component in the CCD, it
produces an electric charge.
• Charge Storage: The charge is stored in the component's capacitor, with the
amount of charge corresponding to the intensity of the light.
• Charge Transfer: The stored charge is transferred to a circuit that generates a
digital signal, which the camera then converts into an image.

Image Formation

• Pixels: The image is composed of small dots called picture elements or pixels.

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 o Color Images: To create color images, the camera uses red, green, and
blue light. These primary colors mix to form all the different colors in the
image.
o Intensity Detection: The intensity of the light hitting each pixel
determines the amount of charge stored, allowing for variations in
brightness and color.

Example: Taking a Picture with a Digital Camera

• Exposure: Light enters the camera through the lens and hits the CCD.
• Charge Accumulation: Each pixel on the CCD accumulates charge based on the
light intensity.
• Signal Conversion: The accumulated charges are transferred to a circuit that
converts them into a digital signal.
• Image Formation: The digital signal is processed to form the final image
displayed on the screen.

Delay in Image Capture

• Processing Time: There is often a slight delay when taking a picture because the
camera needs time to move the charge from the CCD and convert it into a digital
signal.

Electric Fields in Touch Screens

Electric Fields

• Field Concept: Similar to gravitational and magnetic fields, electric fields exist
around electric charges.
• Field Lines: Electric field lines can be drawn to represent the direction and
strength of the field, similar to how magnetic field lines are depicted.
• Interaction with Touch Screens: When you touch a touch screen, you change
the electric field between your finger and the screen's internal plate. The device
detects these changes to determine the location and movement of your finger.

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Understanding Circuit Components and Symbols

Electric circuits are essential for operating many devices, from entertainment systems
to life-saving medical equipment. Understanding the components and symbols used in
circuits helps in designing and interpreting these circuits.

Simple Circuit Example

Basic Components

• Lamp: Provides light when the circuit is complete.

• Battery (Cell): Supplies electrical energy to the circuit.
• Wire: Conducts the electrical current.
• Switch: Controls the flow of current, allowing the lamp to be turned on or off.

Simple Circuit Example

• Torch Circuit: A basic circuit found in a torch includes a lamp, battery, and wire.
Adding a switch allows you to control the lamp.

Circuit Symbols

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Connecting Components in a Circuit

Series Connection

• Series Connection: Components are connected end-to-end, so the same

current flows through each component.
• Battery Connection: When connecting cells in a series to form a battery, ensure
the positive terminal of one cell is connected to the negative terminal of the
next cell.

Parallel Connection

• Parallel Connection: Components are connected across common points, so

each component receives the same voltage.

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Example 1: Simple Torch Circuit

• Components: Lamp, battery, switch, and wires.

• Operation: When the switch is closed, the circuit is complete, and the lamp
lights up.

Example 2: Battery Connection

• Two Cells in Series: Connect the positive terminal of the first cell to the negative
terminal of the second cell. This increases the total voltage available to the
circuit.

What is Electric Current?

Electric current is the flow of electric charge through a conductor, such as a metal wire.
The flow is typically due to the movement of electrons, which are negatively charged
particles.

How Current Flows

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 • In Metal Wires: Electrons move through the metal atoms. These electrons are
not tightly bound to the atoms and can move freely, creating an electric current
when a voltage (electric push) is applied.
• Measurement: Current is measured in amperes (A), often shortened to amps.
For smaller currents, it is measured in milliamps (mA), where 1 mA = 0.001 A.

Measuring Current

• Ammeter: A device used to measure current in a circuit. It is connected in series

with the components of the circuit.
o Types:
▪ Analog Ammeter: Uses a needle and scale to display current.
▪ Digital Ammeter: Shows current on a digital display.
o Symbol:

Series Circuits

A series circuit has only one path for the current to flow.

• Characteristics:
o Single Loop: If one component fails, the entire circuit is interrupted.
o Current: The current is the same through all components because there
is only one path for the flow.
o Example: A simple torch with a battery, lamp, and switch.

Measuring Current in Series Circuits

• Consistency: The current measured at any point in a series circuit is the same
because the current has only one path.

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Conventional Current vs. Electron Flow

• Conventional Current: Flows from the positive to the negative terminal of the
battery.
• Electron Flow: Electrons actually flow from the negative to the positive
terminal. This is the real direction of current flow.

Parallel Circuits

A parallel circuit has multiple paths for the current to flow.

• Characteristics:
o Multiple Loops: Components are connected in separate branches.
o Current: The total current is the sum of the currents through each
branch.
o Example: A circuit with multiple lamps where each lamp can be
controlled independently.

Measuring Current in Parallel Circuits

• Branch Currents: Each branch has its own current. The total current is the sum
of the currents in all branches.

Models of Electric Circuits

1. Factory Model:

• Factory: Represents the battery.

• Trucks: Represent the charges.
• Shop: Represents the lamp.
• Explanation: The factory pushes out charges (like trucks carrying goods) to the
shop (lamp), delivering energy.

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2. Water Circuit Model:

• Pipes: Represent wires.

• Pump: Represents the battery pushing water (charge) through pipes.
• Tap: Acts like a switch to control the flow of water.
• Meter: Measures the flow, similar to an ammeter.

How Components Affect the Current

In Series Circuits

• Adding Components: Increasing the number of components increases the total

resistance, decreasing the current.
• Changing Resistance: Different components provide different resistance. For
example, a buzzer may have higher resistance than a lamp.
• Adding Cells: Increases the voltage, resulting in a higher current.

In Parallel Circuits

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 • Adding Components: Each new component provides an additional path for
current, increasing the total current.
• Voltage: The voltage across each component in a parallel circuit is the same as
the voltage across the battery.

Voltage

Voltage is the electrical force that drives the current through a circuit. It is measured in
volts (V).

Measuring Voltage

• Voltmeter: Used to measure the voltage across a component. It is connected in

parallel with the component.
o Symbol:

Voltage in Circuits

• Series Circuits: The total voltage is divided among the components. If two lamps
are connected in series with a 6V battery, each lamp gets 3V.
• Parallel Circuits: The voltage across each component is the same as the voltage
of the battery.

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