Charging by friction

• Normally the number of protons and electrons in an atom is equal but sometimes it is possible for one object to ‘steal’ electrons from another by being rubbed against it.

• When polythene rod is rubbed with a cloth some of the cloth’s electrons are ‘stolen’ by the rod.

  • The rod is now negatively charged because it has an excess of electrons.

  • The cloth is now positively charged because it has less electrons

  • Both objects are said to be charged with static electricity

Attraction and repulsion

• When two charged objects are brought close to each other they exert a force on each other

• positives repel

• opposites attract

Induced charge

• When a balloon is rubbed with a cloth it can stick to a wall.

• If the balloon is negatively charged it will repel the electrons on the surface of the wall.

• The wall has an induced positive charge therefore the balloon will attract and stick

• If the balloon is positively charged it attracts the electrons and sticks to the wall

Uses

• Photocopier

• Electrostatic sprays

  • The paint as it passes through the nozzle gets positively charged and paint particles start to repel each other.

  • There will be a fine, even spread of paint and the paint will go around the object and into any hidden edges.

  • Less paint wasted

  • If the object is earthed the paint will be attracted to it and

• Electrostatic precipitator

  • Dusts and fumes pass through a high voltage metal grid (-5000V).

  • This makes the dust particles negative.

  • Later on they pass near earthed plates (or positive) and due to induced charge they attract the dust (or due to opposites attract).

  • Eventually the plates get too dirty so the dust needs to be removed, shaken or hit by a hammer to get the dust off

Dangers

• Refuelling

  • Friction through the hose + petrol.

  • Or when a plane flies there is friction between the plane and air

  • The friction transfers electrons, charging the vehicle (or hose when the fuel flows).

  • A spark could cause and explosion with the fuel

  • To prevent this an earth wire is connected.

  • Current flows through the wire, neutralising the charged object

• Lightning

  • Lightning rods safely discharge the lightning onto the ground

Charging by Friction

Normally, the number of protons and electrons in an atom is equal, resulting in a neutral charge. However, it is possible for one object to ‘steal’ electrons from another by rubbing against it, leading to a phenomenon known as charging by friction. For instance, when a polythene rod is rubbed with a cloth, some of the cloth’s electrons are transferred to the rod. As a result, the rod becomes negatively charged due to the surplus of electrons, while the cloth becomes positively charged because it has lost electrons. Both objects are now said to be charged with static electricity.

Attraction and Repulsion

When two charged objects are brought close to each other, they exert electrostatic forces on each other:

• Like charges repel: two positively charged or two negatively charged objects will push away from each other.

• Opposite charges attract: a positive charge will pull a negative charge towards it.

Induced Charge

A common example of induced charge can be observed when a balloon is rubbed with a cloth and then brought near a wall. If the balloon becomes negatively charged, it will repel the electrons located on the surface of the wall, resulting in an induced positive charge on that area. This induced charge attraction causes the balloon to stick to the wall. Conversely, if the balloon is positively charged, it will attract electrons from the wall, also allowing it to adhere to the surface. This principle is key to understanding how static electricity interacts with different materials.

Uses of Static Electricity

• Photocopiers: Photocopiers utilize static electricity principles to transfer images. The surface of the copier drum is charged with static electricity. Paper placed on the drum also becomes statically charged and attracts toner particles, which are positively charged, leading to image reproduction.

• Electrostatic Sprays: In painting applications, the electrostatic spray method charges paint particles positively as they exit the nozzle. This charging causes the paint particles to repel each other, resulting in a fine and even spread of paint. This method helps to ensure that paint reaches hidden edges and reduces paint waste significantly. If the object being painted is earthed, the paint is further attracted to it due to the opposite charges, improving application efficiency.

• Electrostatic Precipitators: These devices are used in industrial settings to control air pollution. Dust and fumes pass through a high-voltage metal grid (around -5000V), which charges the dust particles negatively. As these charged particles then pass near earthed plates (which are positively charged), they are attracted due to the principle of induced charge. Eventually, the plates accumulate dust and need to be cleaned, often by being shaken or struck by a hammer to dislodge the accumulated particles.

Dangers of Static Electricity

• Refuelling: The act of refuelling vehicles can create static electricity due to friction generated during the flow of fuel through the hose. This friction can transfer electrons, thus charging the vehicle. If a spark occurs due to this static charge, it can ignite the fuel, potentially causing an explosion. To mitigate this risk, an earth wire is often used to safely discharge any static electricity that builds up during the refuelling process.

• Lightning: Natural occurrences such as lightning can also be connected to static electricity. Lightning rods are installed on buildings to safely discharge lightning strikes into the ground. This prevents damage and reduces the risk of fire by providing a pathway for the electrical charge to safely dissipate.

Charging by Friction

Normally, the number of protons and electrons in an atom is equal, resulting in a neutral charge. However, it is possible for one object to ‘steal’ electrons from another by rubbing against it, leading to a phenomenon known as charging by friction. For instance, when a polythene rod is rubbed with a cloth, some of the cloth’s electrons are transferred to the rod. As a result, the rod becomes negatively charged due to the surplus of electrons, while the cloth becomes positively charged because it has lost electrons. Both objects are now said to be charged with static electricity.

Attraction and Repulsion

When two charged objects are brought close to each other, they exert electrostatic forces on each other:

• Like charges repel: two positively charged or two negatively charged objects will push away from each other.

• Opposite charges attract: a positive charge will pull a negative charge towards it.

Induced Charge

A common example of induced charge can be observed when a balloon is rubbed with a cloth and then brought near a wall. If the balloon becomes negatively charged, it will repel the electrons located on the surface of the wall, resulting in an induced positive charge on that area. This induced charge attraction causes the balloon to stick to the wall. Conversely, if the balloon is positively charged, it will attract electrons from the wall, also allowing it to adhere to the surface. This principle is key to understanding how static electricity interacts with different materials.

Uses of Static Electricity

• Photocopiers: Photocopiers utilize static electricity principles to transfer images. The surface of the copier drum is charged with static electricity. Paper placed on the drum also becomes statically charged and attracts toner particles, which are positively charged, leading to image reproduction.

• Electrostatic Sprays: In painting applications, the electrostatic spray method charges paint particles positively as they exit the nozzle. This charging causes the paint particles to repel each other, resulting in a fine and even spread of paint. This method helps to ensure that paint reaches hidden edges and reduces paint waste significantly. If the object being painted is earthed, the paint is further attracted to it due to the opposite charges, improving application efficiency.

• Electrostatic Precipitators: These devices are used in industrial settings to control air pollution. Dust and fumes pass through a high-voltage metal grid (around -5000V), which charges the dust particles negatively. As these charged particles then pass near earthed plates (which are positively charged), they are attracted due to the principle of induced charge. Eventually, the plates accumulate dust and need to be cleaned, often by being shaken or struck by a hammer to dislodge the accumulated particles.

Dangers of Static Electricity

• Refuelling: The act of refuelling vehicles can create static electricity due to friction generated during the flow of fuel through the hose. This friction can transfer electrons, thus charging the vehicle. If a spark occurs due to this static charge, it can ignite the fuel, potentially causing an explosion. To mitigate this risk, an earth wire is often used to safely discharge any static electricity that builds up during the refuelling process.

• Lightning: Natural occurrences such as lightning can also be connected to static electricity. Lightning rods are installed on buildings to safely discharge lightning strikes into the ground. This prevents damage and reduces the risk of fire by providing a pathway for the electrical charge to safely dissipate.