Understanding key concepts such as how charges accumulate, interact, and create electric fields, is crucial for excelling in your Physics exams. Our comprehensive overview aligns perfectly with SEAB learning objectives on this topic, ensuring you grasp static electricity thoroughly and can confidently approach exam questions on static electricity.   First, take a minute to watch this quick recap on the basics of static electricity.   

Charges in Static Electricity

In electrostatics, we study how the charges in static electricity work. Specifically, the law of electrostatics states that a negative charge refers to an electron, whereas a positive charge refers to a proton.  Each electron has a charge of 1.6 × 10-19 coulombs (C).  Moreover, you must understand that unlike charges attract, while like charges repel.  

Principles of Static Electricity: Electrostatic Charging by Friction

First, let’s take a look at how electrostatic charging by friction, a basic process of generating static electricity, works.   Before rubbing, both the plastic rod and cloth are electrically neutral, meaning they have an equal number of positive and negative charges.  When rubbed together, the plastic rod transfers some of its electrons to the cloth’s surface. This process causes the plastic rod to lose electrons, resulting in a positive static charge, while the cloth gains these electrons, resulting in a negative static charge. Therefore, after rubbing, static electricity causes the plastic rod to become positively charged and the cloth to become negatively charged.  

Principles of Static Electricity: Electrostatic Charging by Induction

Next, let’s explore how electrostatic charging by induction, a fundamental aspect of static electricity, works. In this section, we will depict two different experiments to illustrate the principles of electrostatic charging by induction and its application in generating static electricity.

Experiment 1: Charging 2 Conductors

The following experiment will illustrate how static electricity can be induced in conductors simply by the presence of charged objects, which is a key principle of static electricity.   To demonstrate electrostatic charging by induction involving two conductors, follow these steps:

1. Place two conductors on insulating stands side by side.
2. Bring a negatively-charged rod near sphere A.
3. While holding the charged rod, move sphere B away from sphere A.
4. Remove the charged rod.

  In doing so, you’ll find that Sphere A acquires an induced charge opposite to the rod’s charge, while sphere B acquires a charge similar to the rod’s charge due to induction. Ultimately, static electricity can be induced in conductors simply by bringing a charged object close to them.  

Experiment 2: Charging 1 Conductor

The following experiment will demonstrate how static electricity induces charges in a single conductor through the proximity of a charged object.   To demonstrate electrostatic charging by induction involving one conductor, follow these steps:

1. Place a metal conductor on an insulating stand and bring a negatively-charged rod near it.
2. Without removing the charged rod, earth the negatively-charged end of the metal conductor (part B) by touching it with your hand.
3. With the charged rod still in place, remove your hand from the metal conductor.
4. Remove the charged rod

  In doing so, the metal conductor acquires a temporary induced charge opposite in polarity to the charged rod’s end, which illustrates how static electricity can induce charges in a conductor by the proximity of a charged object.  

Real-world Examples of Potential Hazards of Static Electricity Resulting from Electrostatic Charging

Example 1: Static Electricity Hazards in Trucks

  Static electricity can accumulate on trucks due to friction between the road and the rotating tyres of the trucks. When a sudden discharge occurs, it may ignite flammable load and cause an explosion.   

Example 2: Static Electricity in Thunderclouds

  Thunderclouds become charged when water molecules collide with air particles. Electrons gather at the bottom of the clouds, and when the accumulation reaches a critical point, ionized air particles create a conducting path for discharging the charges to the ground.  

Electric Field

To grasp the behaviour of static electricity, you must first understand the concept of electric fields: An electric field is a region in which an electric charge experiences a force due to static electricity.  

Drawing the Electric Field of an Isolated Point Charge

An isolated point charge refers to a single electric charge that exists in space without any nearby charges or objects influencing its electric field. This charge generates an electric field around itself, which exerts forces on other electric charges placed in its vicinity.  Always draw field lines from an isolated point charge perpendicular to the charge itself. Also, ensure the lines do not cross, as electric field lines cannot intersect.  To draw the electric field around a positive point charge, begin at the point charge and draw lines directed away from the point charge. But to draw the electric field around a negative point charge, you should draw the field lines from outside, directed towards the charge instead.  

Drawing the Electric Field Pattern between Two Isolated Point Charges

To illustrate this concept, refer to our diagrams below depicting Attraction and Repulsion in electric fields, which show how static electricity influences the interactions among multiple charged particles.  

Repulsion

A conducting sphere with a positive charge would repel other positive charges. Therefore, the arrows would point away from the positively charged centre.  

Attraction

On the other hand, if we were to place a negative charge in the field, it would create a force opposite to the field lines as the negative charge is attracted to the positive charge.  

Real-world Applications of Static Electricity

Static electricity is integral to our everyday lives. To deepen your understanding, it’s important to explore how static electricity is utilised in the following three key applications: electrostatic charging in photocopiers, spray paints, and precipitators, all of which achieve specific desired outcomes.  

Electrostatic Charging in a Photocopier

Static electricity is key in the operation of photocopiers as it facilitates the transfer of toner onto paper to reproduce documents accurately.  

1. When exposed to light, selenium on the drum surface becomes conducting.
2. The white areas of the page reflect intense light onto certain parts of the drum, causing those areas to become conducting. However, parts of the page and their corresponding sections on the drum that are not exposed to light remain insulating.
3. Negatively charged toner is sprayed on the drum surface.
4. The paper passes over the drum, and the negatively charged toner is attracted to the positively charged areas of the paper.
5. The toner on the paper is then melted, creating a permanent image on the paper.

 

Electrostatic Charging in Spray Painting

Static electricity enhances product finishing and minimises waste by ensuring an efficient and uniform application of paint onto surfaces.   

1. Pain droplets from an aerosol become charged by rubbing against the spray nozzle. 
2. The objects to be sprayed on are earthed. 
3. The charged paint droplets are attracted to the earthed object, ensuring even coverage.
4. Droplets with the same charge repel each other, spreading out evenly across the sprayed surface.

 

Electrostatic Charging in a Precipitator

Environmental precipitators use static electricity to capture particulate matter from industrial emissions, contributing to cleaner air and reduced environmental impact.  

1. Smoke particles become negatively charged when they pass through the negatively charged grid. 
2. Air molecules around the rods will become ionised due to the strong electric field in the region between the grid and the plates.
3. Positive ions are attracted back to the plates while negative ions are picked up by the tiny particles of ash and dust.
4. These charged dust particles will then move towards the positively charged plates, where they are collected and eventually removed. 

 

Ready to dive deeper into the exciting world of physics? 

Join our interactive live teaching sessions, where we explore various topics covered in the GCE O Level Physics exams, including fascinating subjects like static electricity and more.   Want a sneak peek? Watch Teacher Xuan Ming demonstrate how to solve this Weighted Assessment question on Flyaway Hairs, explaining its connection to static electricity in a clear and easy-to-understand manner!   Want to see more? Follow us on TikTok @blue3academy for updates on our upcoming sessions!