Static Electricity

Static electricity: electric charge that can be collected and held in one place (static means not moving/changing).

Static electricity is different from current electricity. Current electricity is the continuous flow of charge in a complete circuit.

In static electricity, electrons build up in one place. A current is a pathway through which electrons can travel.

Review from Unit 1

Remember from unit 1, in an atom consists of protons (+1), neutrons (o) and electrons (-1).

Protons and neutrons are in the nucleus of the atom and cannot be changed or moved.

Electrons are in energy levels around the atom and can be taken away by other atoms, or added to by electrons from other atoms.

Uses & Dangers of Static Electricity Using pages 233 & 234 in your

textbook, as well as your own common knowledge, list 10 uses and dangers of static electricity in your notebook.

Uses/Dangers of Static ElectricityUses Dangers1. Used in paint on cars2. Used to decrease air pollution

(removes smoke particles from chimneys; air ionizers)

3. Helps sandwich wrap cling4. Packing peanuts stick

together with static electricity5. Helps blankets stick to you at

night6. Sticking balloons to walls at

birthday parties7. Fun – Van der Graff generator8. Swiffer cloths

1. Anywhere oxygen tanks are used in an enclosed space, can cause explosions (spark)

2. Sparking around fuel tanks can cause explosions (that’s why they have grounded fuel hoses)

3. Lightning

Types of Charges Atoms or objects have a positive charge

when they have more protons than they do electrons. Atoms/objects have a positive charge when they LOSE electrons to another atom/object.

Atoms/objects have a negative charge when they have more electrons than they do protons. Atoms/objects have a negative charge when they GAIN electrons from other atoms/objects.

Atoms/objects have a neutral charge when they have the same number of protons as electrons.

Charges in objects can change...

Neutral objects can develop a positive charge when they lose electrons to other objects.

Neutral objects can develop a negative charge when they gain electrons from other objects.

Positively charged objects can become neutral when they gain electrons from other objects.

Negatively charged objects can become neutral when they lose electrons to other objects.

Electrical Discharge

Electrical discharge is the flow of electricity through a liquid, solid, or gas. The flow of electricity is the flow of electrons.

When you get a static shock, electrons move from the place where they have built up (the static charge) and flow from that place to your body.

Laws of Static Electricity1. Like charges repel (positive pushes

away positive, negative pushes away negative)

2. Opposite charges attract (positive attracts negative and vice versa)

3. Neutral objects are attracted to charged objects.

Laws of Static Electricity... When you rub a balloon on

your head, you add electrons from your hair to the balloon, making it negatively charged.

Two negatively charged balloons will repel each other.

When you put a negatively charged balloon on a wall, the positive charge of the wall moves towards the outside of the wall (opposite charges attract each other). This attraction keeps the balloon stuck to the wall.

Visualizing Charge Transfer – Page 231.

In your notebooks, follow steps 1 to 8 in activity 7-1B.

Electric Force and Charge Electric force is the push or pull between

charged objects. Electrical force is an action-at-a-distance force – it can apply force to an object without touching it.

When you touch a negatively charged object to a neutrally charged rod, electrons get added to the rod, making it negatively charged. Charging a neutral object by touching it to a charged object is called charging by conduction.

Touching the neutral rod with a positively charged object would have the same effect. Electrons in the neutrally charged rod will be attracted to the positively charged object . The neutral rod will lose electrons and have a positive charge.

Charging by Induction

If you bring a negatively charged object near, but not touching, a neutral rod, the negative charge will repel the electrons in the rod. The electrons will move down and away from the negatively charged object, and the top will be positively charged. This is called charging by induction. When you move the negatively charged object away, the charges will balance again.

When an object is charged by induction , no electrons get transferred from one object to the next. A change in the position of the electrons inside the object is induced.

Charging by induction explains the third law of static electricity (neutral objects attract charged objects – remember the example of the balloon and the wall).

In your notebooks…

Using pages 233, 234 and 241 in your textbook, explain how the following three technologies work. Make sure to include static electricity in your descriptions.1. Lightning Rod2. Photocopier3. Electrostatic air cleaner

List three careers that relate to electricity.

Pages 246 & 247

Answer questions 1 to 9, 11 to 22,

25 & 26.

Energy… Some Definitions

Energy, in science, is the ability to do work.

Work is force acted through a distance. If you haven’t changed places (distance) you haven’t done any work.

Electrical work is the work done on a charged particle in an electric field.

An electric field surrounds a charged particle, and exerts a force on another electrically charged object.

Potential Energy

Potential energy is stored energy. When you are not moving, you have potential energy (the potential to start moving). When you start moving, your potential energy is converted to kinetic energy (the energy of movement). Think of a mousetrap.

Electric potential energy is energy stored in electrons… the electrons have stored energy and the ability to do work.

Batteries

Batteries use electric potential energy. The battery must be connected to a device for the electrons to lose their stored energy. If you connect a battery to a light bulb, for example, the electric potential energy gets moved through the wire inside the bulb and gets converted to heat and light energy.

Potential energy, electric or otherwise, always gets converted to another form of energy.

Electric Potential Difference Electric charge is measured in coulombs (C).

One coulomb is the amount of charge passing a point in one second when one ampere of current is flowing.

The current is the amount of charge passing a point in a conductor every second.

A conductor is any material that allows electrons to flow freely through it.

An ampere (A) is a unit for measuring electric current.

The amount of electric potential energy per 1 coulomb of charge is the electric potential difference (or just potential difference). This is also called the voltage, and is measured in volts (V).

Electrochemical Cells

Electrochemical cells are also called batteries. They convert chemical energy into electrical energy stored in charges.

Chemical energy separates the +ve and –ve charges – this is why batteries have +ve and –ve ends.

A basic battery consists of: Two electrodes & An electrolyte (either a wet paste or a

solution)

Batteries continued… Electrodes are usually metals, but

can be a metal and another material. The electrolyte is a substance that

conducts electricity. In this example, the electrolyte

attacks the zinc electrode and pulls atoms off of it.

The zinc atoms leave behind electrons on the electrode, and it become -vely charged.

The electrolyte also pulls electrons off the copper electrode. This means that it will become +vely charged.

The difference in charges creates a potential difference (voltage) between the two electrodes.

The amount of voltage produced depends on the types of metal and the electrolyte used. Most electrochemical cells produce 1.5V or 2.0V. A 12V car battery would have six 2.0V cells or eight 1.5V cells connected together with wires.

Questions page 259

Answer questions 1 to 8

Electric Circuits

Electric circuits are complete pathways that allow electrons to flow. In a circuit, electric potential energy is transformed into other forms of energy.

We have already learned that current electricity is the flow of charged particles in a complete circuit.

An ammeter Is a device used to measure current.

To have a continuous flow of charge, a circuit must contain at least one source of voltage.

Electric Circuits

Electric CircuitsThere are four basic parts to an electric circuit:1.The source : the source of the electrical

energy. The source provides electric potential energy to be used by the other elements of the circuit. This creates a potential or voltage drop (i.e. the sources starts getting used up). This could be a cell, a battery, or a generator.

2.The conductor: the wire that the electric current flows through.

3.The load: a device that transforms the electrical energy into other forms of energy (a light bulb, a buzzer, a heater, a motor).

4.The switch: a device that can turn the circuit on or off by closing or opening the circuit.

Circuit Diagrams Circuit diagrams are simple drawings

that demonstrate the different components of a circuit. To draw them we use the following symbols:

ammeter

Circuit diagrams

Some notes on circuit diagrams…. Ammeters are always connected in

series. This means they will be in the same line as the source and load.

Voltmeters are always connected in parallel. This means that they will be draw in a separate box or triangle connected to the series.