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Science 9- Unit 4
Transcript of Science 9- Unit 4
and Technologies Unit 4
Topic 1 - Electric Charge
When you get a 'shock', feel a 'jolt', or, a 'spark', you are experiencing the same type of electrical
effect that makes lightning Static electricity happens when there is an imbalance of electrons
(which have negative charges)
Producing Charges Making Sense of Electrical Charges Conductors, Insulators, and In-Between Neutralizing Unbalanced Charges Preventing Electrostatic Buildup
Materials that attract or repel other materials are said to be charged, or carry an
electric charge Charges are produced
when materials are
moved together and then separated. To refer to charges as stationary, would be inaccurate, because the charges are moving. ‘Unbalanced charges’ is a more accurate way of describing this
electricity. (Remember! - like charges repel -
Most objects have the same number of positive (proton) and negative (electron) charges This makes them neutral (no charge).
When there is a difference in the electrical charge,
certain actions are predictable, because of the
Laws of Electrical Charges. The charged electrons repel the electrons in the neutral object and the charged object is then attracted to the protons of the neutral object.
In insulators electrons are bonded closely to the nuclei (allowing little movement), while in
conductors, the electrons are free to move easily Most metals are conductors and non-metals are insulators. A special type of conductor, called a resistor allows electrons to flow, but provides
some resistance (so it is sort of in-between a conductor and insulator) Superconductors are materials that offer little, if any, resistance to the flow of electrons.
There is now an electron balance.
An ionizer can be used to neutralize
charges on non-conductors Anitstatic sprays, coating or grounding strips P. 266 in your textbook A rubber belt rubs a piece of metal and transfers the charge to a sphere. When you touch the
sphere the charge builds up on you. These generators build up an excess of static charge using friction. A Van de Graaff generator that is why your hair
strands separate as you touch the sphere as the charge builds up on your body.) 5:18 Minutes
Benjamin Franklin was the first to describe the charges as ‘positive’ or ‘negative’. Law of Charges:
1. Unlike charges attract.
2. Like charges repel.
3. Charged objects attract (neutral) objects. Copper wire = conductor porcelain = insulator Porcelain toilets too! Semiconductors are almost perfect
conductors they have almost no resistance to electron flow. Silicon semiconductors are used extensively to make computer microchips. Electrical Discharge is the movement of charges whenever an imbalance of charges occurs. The action results in neutralizing the objects. The over-charged electrons repel the electrons in the object and the positive protons attract the charged electrons causing a discharge or 'miniature lightning bolt'. ‘Static cling’ is a build-up of unbalanced charges on different materials.
Topic 2 - Electricity Within a Circuit Circuit Elements and Diagrams Measuring Current Measuring Voltage Rivers of Electricity A circuit is a pathway that allows the flow of electricity. Most electrical circuits use wires
(as conductors), although others may use gases, other fluids or materials. • load - converts electrical energy into another form of energy …
Bulb All circuit diagrams have four basic parts: • source - provides energy and a supply of electrons for the circuit
… Battery • conductor - provides a path for the current …Wires • switching mechanism - controls the current flow, turning it off and on, or directing it to different parts of the circuit
A drawing made with these symbols is called a schematic or schematic diagram.
The rules to follow when making schematic diagrams:
Use a pencil and ruler on graph or unlined paper
Place the components in a rectangular or square arrangement
Conducting lines should be straight with ‘right-angled’ corners
Do not cross conductors
Be neat and make the sizes of the symbols consistent and easy to see
The steady flow of charged particles is called electrical current The flow continues until the
energy source is used up, or disconnected. The rate at which an electrical current flows is
measured in amperes (A). This flow varies from a fraction of an ampere to many thousands of
amperes, depending on the device. An instrument used to measure very weak electric current is
called a galvanometer. Larger currents are measured with an ammeter
Electrical energy is the energy carried by charged particles Voltage is a measure of how much electrical energy each charged particle carries. The higher the energy of each charged particle,
the greater the potential energy. Also called 'potential difference' MEASURING CURRENT
Topic 3 - Resisting the Movement of Charge
Resistance is a measure of how difficult it is for the electrons to flow through a conductor. Resistance also converts electric energy into other forms of energy. conductors have low resistance and insulators have high resistance. The standard unit for
resistance is ohm (Ώ). Resistance can be measured directly with an ohmmeter, but a multi-meter
is used more often to measure resistance.
Electrical resistance is calculated by finding the ratio of the voltage across the load (V) to the
current through the load (I). This is called Ohm’s Law. R = V / I
The more resistance a substance has, the greater the energy gain it receives from the electrons
that pass through it
Topic 5 - Portable Power Electrochemical Cells Two metal electrodes are surrounded by an electrolyte. The chemical reaction in a cell releases free electrons The chemical reactions within the cell determine the potential difference (voltage) that the cell can create. Several cells connected in series produces a higher voltage, and is commonly referred to as a battery, which is a sealed case with only two terminals. A primary cell is one in which the reactions will not continue after the reactants are used up. A secondary cell uses chemical reactions, which can be reversed. These are referred to as rechargeable batteries. Wet cells
use a liquid electrolyte. Wet cells are 'wet', because the electrolyte is a liquid (usually an acid). The acidic electrolyte eats away the zinc electrode, leaving behind electrons that give it a negative charge. The copper electrode is positive, but it is not eaten away. –the electricity-producing cells, referred to as 'batteries', the chemicals used in them are a paste. Dry cells The dry cell is made up of two different metals, called electrodes in an electrolyte. An electrolyte is a paste or liquid that conducts electricity because it contains chemicals that form ions. The electrolyte reacts with the electrodes, making one electrode positive and the other negative. These electrodes are connected to the terminals.
Topic 6 - Generators
A device that converts mechanical energy into electrical energy is called an electric generator (energy of motion – windmills, turbines, nuclear power,
falling water, or tides)
Electricity to Magnetism found that the current created a
magnetic field around the wire. Hans Christian Oersted The amount of needle deflection depended on how much electric
current was flowing in the wire. When the current was reversed, the needle moved in the
opposite direction. The strength of an electromagnet is affected by the …
type and size of core
strength of current
number of coils What do you think could increase the power of electromagnets? Michael Faraday
(and Joseph Henry) discovered electromagnetic induction in 1831. Faraday created the first
What’s in a Generator? An AC generator – the most common type – has a coil of wire rotating inside a stationary field
magnet. The electricity produced by this type of generator is called alternating current because it changes
direction in North America it changes direction 120 times per second – giving 60 Hertz or
complete waves each second. A DC generator is much the same as a DC motor, and is often called a dynamo. The DC generator’s pulsating
electricity is produced in one direction - referred to as direct current - and coincides with the
spinning of the generator.
Faraday constructed the first motor
AC motors have a rotating core Topic 7 - Electricity in the Home Transmission of Electricity through the Power Grid Transformers are used to change the amount of voltage with hardly any energy loss. Voltage change
is necessary because the most efficient way to transmit current over long distances is at high voltage
and then reduced when it reaches its destination, where it will be used. A step-up transformer increases voltage a step-down transformer reduces voltage just before
entering your home. Why do you think that's a good idea? Increase the voltage, only to decrease it later... From the Grid into Your Home Coming in contact with a power transmission line can prove to be deadly. By touching it, a short
circuit can occur, because the electricity is trying to find a path to the ground - you can complete
the circuit, and it may be fatal. Power needs to enter your home safely. Electrical power enters a meter on the side of your house where electrical usage is recorded Power is then routed into the service panel
(usually in the basement). The main circuit breaker
shuts off all the power in the house at once, in case of an overload. The individual circuit breakers in the service panel
control the branch circuits, located throughout the entire house. Each branch circuit is connected in parallel to wall plugs, lights and wall
switches within a particular area of the house. Home Wiring
To install or change electrical wiring in your home a permit is necessary and all work done must meet a set of standards called the electrical code