Untitled Flashcards Set

All matter is made up of tiny particles called atoms.  Atoms have 3 parts:

• Protons have a positive electric charge.

• Neutrons do not have an electric charge.

• Electrons have a negative electric charge.

An electrically neutral atom has equal numbers of positive and negative charge.  Electrically neutral objects neither attract nor repel each other.

Any object can become electrically charged by giving away or receiving electrons:

• If an object gives away electrons, it becomes positively charged.

• If an object receives electrons, it becomes negatively charged.

• An unbalanced negative or positive charge on an object is called a static charge.

Charged objects can apply electric forces to one another.

Electric forces are different from traditional forces in that they can push or pull on other electric charges without touching.

Like charges (+/+ or -/-) will repel, or push each other away.  Opposite charges (+/-), on the other hand, will attract each other.

Coulomb’s Law tells us two things:

1. The more electric charge is present on two charged objects, the stronger the electric force between those charged objects will be.  They are directly related.

2. The farther apart two electric charges are, the weaker the electric force between them will be.  They are inversely related.

A material that electrons can easily move across is called a good conductor of electricity.  Metals and water are good conductors.

A material that electrons can not easily move across is called a good insulator of electricity.  Materials such as rubber, plastic, wood, and glass are good insulators.

There are 3 ways to electrically charge an object:  conduction, friction, and induction.

1. Conduction is the transfer of electric charge by simple touch.  Conduction happens when electric charges flow from one conductor to another (usually between metals).

2. Induction is the transfer of electric charge by scrambling electrons in conducting materials.  A charged object scrambles the electrons in two conducting materials it is brought near by repelling the electrons in the conductors so that more electrons are on the far object (see page 351 for diagram).  When the conductors are separated, the charges are trapped and can’t return to where they were before.

3. Friction is charge by rubbing.  One object scrapes electrons off of another object, and both become charged in the process.  For example, when you blow up a balloon and rub it against a sweater, the balloon scrapes electrons off of the sweater, and becomes negatively charged.  The sweater has lost electrons and becomes positively charged.

When electrons concentrate, or scramble at one end of an object, the object is said to be polarized.

When unbalanced charges become balanced, such as when you shock yourself on a metal doorknob after scuffing your feet on a rug, this is called electric discharge.

Lightning is a good example of a large discharge of static electricity.

Scientists are not completely sure of the causes of lightning.  We do know that as cold water droplets, ice crystals, and hail fall through a storm cloud, the scrape electrons off of rapidly rising warm air molecules.  This causes the bottom of storm clouds to become negatively charged.  The negative charge in the storm cloud is attracted to positive charge in the ground/buildings/trees, and discharges in the form of a lightning bolt.

The movement of electrically charged particles (electrons) is an electric current.

A closed, or complete path in which an electric current can travel is called an electric circuit.  

• If the circuit is closed, then there is a complete path and the electricity will flow.

• If the circuit is open, then there is some break or gap in the circuit, and the electricity will NOT flow.

The battery serves as a storehouse of electrical energy.  Chemical potential energy is stored here and turned into electrical energy as electrons flow through the complete circuit.

In a simple, closed circuit, electrons flow from the negative end of the battery, through the wires, through any electrical devices that the circuit powers, and back through more wires to the positive end of the battery.

A couloumb is how scientists count the number of electrons in a circuit.  Since electrons are so small, we use Coulombs of charge to describe them.  One Coulomb of electrons is about 6 x 10¹⁸, or 6 quintillion.

Current is the measure of how much charge is flowing through a circuit at any given moment.  

• We can think of current as being similar to water flowing out of a faucet.

• In the metric system, current is measured in Amperes.

• 1 A of current means that 1 coulomb of charge flows through a wire every second.

Resistance is a measure of how difficult it is for electrons to flow through a material.

• ALL electrical devices operate on the idea of resistance.  It’s how we get useful work from electricity.

• The more resistance in an electrical circuit, the greater the workload on the electrons.

• In the metric system, resistance is measured in Ohms.

A good conductor of electricity has low resistance.  A poor conductor of electricity has high resistance.

Thicker wires have lower resistance than do thinner wires.  Longer wires have higher resistance than shorter wires.

Voltage is the amount of energy the source uses to move electrons through an electric circuit.  Voltage is the “push” on the electrons, forcing them through the circuit.

• In the metric system, voltage is measured in Volts.

• The more voltage, the stronger the forward push on the electrons.

Batteries offer voltage of between 1.5-9 V.  Wall outlets offer voltage of about 120 V.

Ohm’s Law tells us the relationship among current, voltage and resistance in a circuit.

• The greater the voltage in the circuit, the greater the current will be.  Voltage and Current are directly proportional.  

  • This makes sense because if you push the electrons harder, they’ll go faster.

• The greater the resistance in the circuit, the less the current will be.  Resistance and Current are inversely proportional.  

  • This also makes sense because if you make the electrons work harder, they won’t want to move as fast.

The three basic parts of an electric circuit are:

1. Source of electric energy 

2. Electrical devices that transform electrical energy

3. Conductors such as wires that connect everything

Batteries are sources of electrical energy.  All batteries have two electrical contacts:  positive (+) and negative (-).

When a complete path exists between a battery’s negative and positive terminals, we say that the circuit is a closed circuit.

Electrons flow from the negative end of a battery to the positive end of the same battery.  They must flow through the wires and electrical devices in the circuit to reach the positive terminal.

Electrical devices, or appliances, convert electrical energy to other forms, such as thermal energy or light.  Electrical appliances are a source of resistance in a circuit.  

Whenever electrical energy flows through a circuit, some of the energy is wasted as thermal energy.

There are two ways to connect multiple electrical appliances in a circuit:  Series circuits and Parallel circuits.

In a series circuit, there is only one path for the current to flow.  Resistance in such a circuit is very high, and the current is very low.  Bulbs or other devices in the circuit are usually very dim as a result.  If one of the bulbs in the circuit burns out or is unscrewed, the entire circuit stops working, as there is no complete path for the current to flow.

In a parallel circuit, there are many paths for the current to flow.  Resistance in such a circuit is much lower than in a series circuit, and current is higher, since each electron only has to flow through one appliance.  Bulbs or other devices in the circuit are much brighter than they would be in series as a result.  If one of the bulbs in such a circuit burns out or is unscrewed, the rest of the circuit will usually keep working, as there are still complete paths for the current to take.  

Homes and schools are wired in parallel.

Fuse Boxes and Circuit Breakers are important electrical safety devices in your home.  Their job is to automatically open a circuit if the current becomes too high.  Too much current through a circuit can get it hot enough to cause a fire.

Any complete circuit with no resistance (i.e. it’s connected to a battery, but not to any light sources or appliances) is called a short circuit.  Short circuits are very dangerous because of how hot they can get.

Electric current follows the path of lowest resistance to the ground.  That path might be through an electric conductor such as metal, water, or even your own body.

Electric shock occurs when electric current flows through your body.  If you touch a current carrying wire or a damaged appliance while touching the ground, electric current could pass through your body, giving you a dangerous shock.