Electrical Charges & Fields

What is a charge?

A physical quantity of matter that dictates howit reacts in an electrical field.

How do charges interact?

Like charges repel. And opposite charges attract.

Where do charges come from?

The protons and electron in our atoms

What dictates the movement of elecrons?

Different materials have different levels of electron affinity that decides how much an atom ‘wants’ an electron and how willing the substance is to accept electrons from other materials.

What is the process of ‘charging by friction’?

When two materials are rubbed together, the material with the higher electron affinity recieves electrons (becoming negatively charged) while the material losing the electron gains a positive net charge.

→ The friction releases the heat energy that gives the electrons energy needed to move over and transfer to the other material.

Which charged particle is the only one that moves?

Electrons are the only charged particles that move because they are weakly bonded making it easier to break their bonds with low amount of energy.

Describe the differences between conductors/insulators/semi-conductors

• Conductors = have loosely bound electrons that can move freely from atom to atom. Allowing electrons to spread out and flow easily through the substance, minimising build up of electrostatic charge.

• Insulators = Electrons are tightly bound to atoms and cannot flow freely. Meaning if charge is transferred through them they don’t flow easily, creating a build up of electrons that can’t move out of place —> electrostatic charge

• Semi-Conductors = bad conductors when cold (less energy for electrons to flow) but good conductors when hot (more energy for electrons to flow

How are uncharged objects attracted to charge ones?

When a charged object (positive or negative) is held near an uncharged one, the like charges will repel and the opposite charges attract.

E.g if a negatively charged object was held near an uncharge one, the electrons in the uncharged one will move oppositely and repel. Creating a build up of positive charge on the surface and negative charge at the bottom. The force of attraction is stronger than the force of repulsion as the charges are closer, causing the charged object to attract the uncharge one.

How does charging by induction work for a positive overall charge?

1) A negatively charged rod is held near the neutral sphere

2) The electrons move away from the rod to repel, leaving one side of the sphere positive and the other negative

3) The negative side is earthed, forcing the electrons into the ground by conducting material.

4) When the conducting material is removed the overall charge in the sphere is positive as the electrons have transferred into the ground

How does charging by induction work for a negative overall charge?

1) A positively charged rod is held near a neutral sphere at the top

2) The electrons will move to attract in the direction of the positively charged rod, leaving a negatively charged top and positively charged bottom.

3) The positvely charged bottom is earthed to the ground and electrons will move up the conducting material to neutralise the protons.

4) When the conducting material and rod is removed the electrons will spread out to fill the neutral space creating an overall negative charge

What is static electricity?

The buildup of electric charge on the surface of a material (mostly insulating material) due to friction between two materials

How do we discharge electrons to the Earth through the body?

If an insulating material continues to recieve a transfer of electrons that build up as a result of its strongly bonded electrons, its potential difference to the neutral charge of the Earth increases. If its potential difference is significant, when it comes in contact to a ‘earthed object’ the electrons will tend to jump across to to earthed object (in this case your body).

How do photocopier work using eletrostatic charge?

1) A light sensitive plate is given a positive net charge

2) An image of the original photo is projected and the blank areas are neutralised with electrons while the dark areas remain positively charged.

3) Negatively charged powdered ink (toner) is spread across the plate, sticking to the positively charged area through oppositely charged attraction

4) A paper is placed over the plate and heated so that the powdered ink can melt an stick to the paper, leaving behind the original image.

How do electrostatic precipitators work using electrostatic charge ?

1) Waste gas alongside ash and soot entire via a duct

2) The particles flow up the precipitator while positively charged plate and negatively charged wires are attached to the sides.

3) The negatively charged wires ionizse the ash and soot particles

4) The positive plates attract the negatively soot.

5) The neutrally charged waste gas pases up without inturuption and floats out clean

What is a ‘field’?

A region in space where a particular force occurs

What are the 3 different fields?

• Gravitational field = anything to do with mass pulling another mass

• Electrical field = anything to do with two charges attracting or repelling.

• Magnetic fields = anything to do with two poles attracting or repelling

How are the fields shown between positive and negative particles?

The fields are shown using field lines. Must be drawn perpendicular to surface and go from positive to negative

How does strength in the fields differ?

The strength of the field is more concentrated closer to the particles and gets weaker the further away they are.

What is the process of ionising air?

1) A strong electrically charged rod is held against neutral air particles

2) The electrons in the air push and repel away as the electrons jump.

3) Ionising the air and leaving negatively charged electrons to freely move