TOPIC 2 - Electric charge (Static electricity experiments in notebook) (copy)

What is static electricity?

Static electricity is a build up of electric charge on an object.

- Identify 4 Insulating materials

Plastics, rubber, wool, and wood.

- Identify a Conducting material

All metals - copper is the best conductor

What is a conductor?

A conductor is a material that allows charge (usually electrons) to flow through it easily.

How does a conducting material allow charge to flow through it?

- Conductors are made up of positively charged metal ions, with their outermost electrons delocalized - the electrons are free to move.
- The sea of delocalized electrons carries the current throughout the metal.

What is an insulator?

An insulator is a material that has no free charges, hence does not allow the flow of charge through them.

How does an insulating cause charge to build up?

- Insulating materials do not have delocalized electrons to carry a charge throughout the material, so the charge builds up instead.
- Although insulators don't conduct electricity, they do conduct a little in the form of static electricity.

Explain how positive and negative electrostatic charges are produced on materials

- When a substance or object becomes STATICALLY CHARGED, only electrons are transferred.
- The electrons orbit around the nucleus of an atom, and it is relatively easy to remove/add electrons from/to a substance.
- If electrons are ADDED, the substance has an overall NEGATIVE charge.
- If electrons are REMOVED, the substance has an overall POSITIVE charge.

Atoms consist of three types of particle: PROTONS

Positively charged particles found in the nucleus.

Atoms consist of three types of particle: NEUTRONS

Neutral particles found in the nucleus.

Atoms consist of three types of particle: ELECTRONS

Negatively charged particles which orbit the nucleus in 'shells.'

Opposite charges...

Attract

Like charges...

Repel

Explain electrostatic phenomena in terms of the movement of electrons

- All objects are initially electrically neutral: the negative (electrons) and positive charges are evenly distributed.
- When the electrons are transferred through friction, one object becomes negatively charged and the other positively charged.
- This difference in charges leads to a force of attraction between itself and other objects which are also electrically neutral.
- This is known as static electricity.

Name the 3 ways in which materials can become charged

1. Friction - rubbing two uncharged objects together.
2. Contact - a charged object is put in contact with an uncharged object.
3. Polarization - a charged object is put NEAR an uncharged object.

- How do planes become charged during flight?
- How do they become neutralized before refueling?

- The friction of air particles rubbing against plane while travelling through atmosphere builds up.
- Earth the plane (connect a conducting wire between the plane and earth) so that the charge flows safely to earth, and the plane becomes neutral again.

- Explain the dangers of electrostatic charges when fulling an aircraft or tanker

- Fuel runs through pipes at a fast rate.
- This fuel is very flammable.
- The friction between the fuel (a liquid insulator) and the pipe causes the fuel to gain charge.
- Uncontrolled discharging could cause a spark and result in an explosion.

How do you reduce the risk of an explosion when fueling an aircraft or tanker?

- Slow fueling
- Earthing the equipment and vehicle

Explain the uses of electrostatic charge in photocopiers

- Photocopiers use static electricity to ATTRACT the small particles of ink onto the paper in the right places:
1. Image is projected onto a POSITIVELY charged copying plate.
2. When light is projected onto the plate, the charge leaks away, except where the image is.
3. NEGATIVELY charged black toner particles are attracted to the remaining positively charged areas (where the image is.)
4. Paper is placed over copying plate: toner is transferred to paper and heated to make it stick.
5. Paper removed from copy plate.

Explain the uses of electrostatic charges in inkjet printers)

- Inkjet printers use static electricity to DEFLECT the small particles of ink onto the paper in the right places.
1. Each ink droplet is charged.
2. POSITIVELY charged - it is repelled by the positive plate and attracted to the negative plate.
3. By controlling the potential difference between the plates, ink droplet hits the paper in the desired place.

Describe an experiment to investigate how insulating materials can be charged by friction - Gold leaf electroscope

a variety of plastic rods and dusters, and a gold leaf electroscope are needed…

1. charge the electroscope using a high voltage supply. note whether its positively or negatively charged.

2. rub an insulator with a duster. Hold insulator close to electroscope.

3. due to the movement of the electroscope leaf, deduce the following:

   • insulator is charged.

   • sign of the charge.

     repeat experiment with other dusters and insulators. record results.

   • same charge = like charges repel = the Gold leaf rises

   • opposite charge = negative charge from the rod pushes electrons away in the leaves, leaving them with a positive charge.

Describe an experiment to investigate how materials can be charged by friction

rub two insulators together…

1. rub a woolen cloth and plastic rod together.

2. one looses electrons and the other gains electrons. The cloth and ruler become oppositely charged.

3. charge 2 of the same plastic rulers with the same cloth.

4. suspend one plastic rod from string and bring second ruler close to it.

5. the suspended ruler repels from the other because they have the same charge.

6. REPEAT EXPERIMENT WITH PLASTIC AND GLASS ROD

7. if the 2 rods are oppositely charged, plastic rod is attracted to glass rod.

Describe an experiment to investigate how materials can be charged by contact

1. charge plastic rod by rubbing with a cloth.

2. bring charged rod in contact with neutral metal sphere.

Negatively charged rod

• electrons transferred from negatively charged rod to metal sphere.

• sphere is a conductor. electrons spread out over it.

• metal sphere is becomes negatively charged (like the plastic rod)

Positively charged rod

• electrons transferred from metal sphere to positively charged rod (electrons attracted to the rod.)

• sphere becomes positively charged (like the plastic rod.)

Describe an experiment to investigate how materials can be charged by polarisation

Negatively charged rod

1. electrons in section of sphere closest to the negatively charged rod are repelled.

2. leaving the section nearest positively charged.

3. and the section furthest away, negatively charged.

Positively charged rod

1. electrons in sphere attracted to positively charged rod.

2. leaves section nearest negatively charged.

3. and section furthest away negatively charged.

in both cases, if you take the rod away, the charge of the sphere will redistribute and become unpolarised.