Science 9 Unit 3 Review: Ch 7,8,9

Front 1

7.1

Static Charge

Back 1

Static charge is an electrical charge that is collected in one place.It is often encountered in everyday life when objects rub against one another and transfer charge

Front 2

Positive and Negative Charges

Back 2

All matter is made of atoms.Protons (positive) and neutrons (neutral) are found at the centre of the atom in the nucleus.Electrons (negative) surround the nucleus.

Front 3

Positive and Negative Charges

Back 3

Solid materials become charged due to the movement of electrons.When electrons are gained, the object becomes negatively charged.When electrons are lost, the object becomes positively charged.Electrons are transferred through friction, when objects rub against each other.

Front 4

Insulators and Conductors

Back 4

Materials that do not allow charges to move easily are called electrical insulators.Materials that allow electrons to travel freely are called electrical conductors.Only insulators are good at retaining static charge.Charge is measured with a unit called the coulomb (C).

Front 5

Generating Static Charge

Back 5

Van de Graff generators use friction to produce large amounts of static charge.As a rapidly moving belt moves over rollers, contact between the two results in a transfer of charge.The moving belt produces static charge on a metal dome.

Front 6

Applications and Dangers

Back 6

Electrostatic filters can be used to clean air, paint automobiles, and hold objects with electrostatic attraction.When static charge builds up, it can discharge and cause serious shocks, explosions or fires.Lightning is especially dangerous and is generated by static charge in the atmosphere.

Front 7

7.2

Force

Back 7

A force is a push or a pull.Eg. Shooting a basketball or pulling a wagon.Forces that are directly applied (ie. through direct contact) are known as contact forces.

Front 8

Electric Force

Back 8

Electric force can push or pull both without touching the object.It is also known as an action-at-a-distance force.Electric force involves the attraction or repulsion of charged objects.

Front 9

Laws of Static Charge

Back 9

Like charges repel.Opposite charges attract.Neutral objects are attracted to charged objects.

Front 10

Charging by Conduction

Back 10

Charging through direct contact.Extra electrons will move to a location where there is less of them.Electrons are transferred between the objects

Front 11

Charging by Induction

Back 11

Bringing a charged object nearby a neutral object will cause charge movement and separation in the neutral object.Electrons are not moving from one object to another, they are simply rearranging themselves.

Front 12

Attraction of Neutral Objects

Back 12

Neutral objects and charged objects attract each other by induction.Eg. When a balloon is rubbed on a person’s hair, it becomes negatively charged. When brought next to a neutral wall, the charged particles in the wall will rearrange and the balloon will stick to the wall.

Front 13

8.1

Energy

Back 13

Energy is the ability to do work or to make things move or change.Energy can be stored in electric charges within batteries so that it can be used later to do work.

Front 14

Electrochemical Cells

Back 14

Electrochemical cells convert chemical energy into electrical energy.Connecting electrochemical cells together creates batteries.The ends of the batteries are known as terminals.Connecting the terminals allows electrons to flow from the battery through a device that converts electric energy into different forms of energy (ie. heat, light, sound)

Front 15

Electrochemical Cells

Back 15

A battery provides energy to push negative charges (ie. electrons) through conductors.A battery has two terminals called electrodes.One terminal is positively charged the other is negatively charged.

Front 16

Electrochemical Cells

Back 16

A battery’s electrochemical cells can be wet cells or dry cells.In dry cells, the electrolyte is a moist paste.In wet cells, the electrolyte is a fluid.Electrons build up at one terminal, leaving it negatively charged and are withdrawn from the other terminal leaving it positively charged.

Front 17

Electric Potential Energy

Back 17

Electric energy can do work.Electric energy that is stored is potential energy.When energy is moving, it is known as kinetic energy.The amount of electric potential energy per coulomb of charge is called the potential difference (ie. voltage).Extra electrons will move to a location where there are less of them.

Front 18

Producing Voltage

Back 18

Electrodes in an electrolyte chemically react to produce electrons.Different charges are created on each electrode.This difference in charge is called potential difference (ie. voltage).

Front 19

Measuring Voltage

Back 19

Voltage is measured in volts (V).A voltmeter is a device that measures the amount of potential difference (ie. voltage) between two locations of charge separation

Front 20

8.2

Electric Circuit

Back 20

An electric circuit is a complete pathway that allows electrons to flow.Electrons flow through devices (ie. loads) in the circuit that convert electricity into other forms of energy.Eg. Radio (sound energy).

Front 21

Basic Circuit Components

Back 21

Source: gives the circuit a source of energy.Conductor: wire where current flows.Load: turns electricity into other forms of energy.Switch: turns the circuit on or off.

Front 22

Circuit Diagrams

Back 22

Circuit diagrams give an organized representation of an actual circuit.

Front 23

Current Flow

Back 23

The continuous flow of charge in a complete circuit is called current electricity.Electric current is defined as the amount of charge passing a point in a conductor every second

Front 24

Current Flow

Back 24

Current is measured in amperes (A).An ammeter is device used to measure current.

Front 25

Conventional Current

Back 25

The flow of electricity is from negative to positive (ie. the flow of electrons).Originally, scientists mistakenly believed electricity flowed from positive to negative.Descriptions of this flow from positive to negative still exist today. It is known as conventional current.

Front 26

8.3

Resistance

Back 26

Resistance is the property of any material that slows down the flow of electrons.Some resistant materials (ie. loads) are able to convert electrical energy into other forms (eg. lamps).

Front 27

Measuring Resistance

Back 27

Resistance can be measured in circuit using an ohmmeter.The unit of measurement for resistance is the ohm (Ω).

Front 28

Ohm’s Law

Back 28

Ohm’s law is an equation that shows how voltage, current, and resistance are related.As the resistance in a circuit increases, the current decreases (ie. slows down). Ohm’s Law:Voltage (V) = Current (I) x Resistance (R)

Front 29

Applications of Resistance

Back 29

Specific resistors are used to control the amount of current in an electrical circuit.Eg. Volume controls, coils in electric stoves.Circuit resistors are marked with coloured bands to indicate their resistance in ohms.The colours indicate different values of the resistance.

Front 30

Applications of Resistance

Back 30

The colour of the first band indicates the first digit.The colour of the second band indicates the second digit.The colour of the third band indicates the number of zeros.The fourth band indicates the percentage accuracy of the resistor.Gold is 5%, silver is 10%, no colour is 20%.

Front 31

Reducing Resistance

Back 31

Semiconductors have conductivity that varies with temperature. Eg. SiliconSuperconductors have zero resistance but require very low temperatures.Eg. Mercury or lead alloysVariable resistors allow resistance to be adjusted.Eg. Dimmer switches and volume dials.Orange, Red, Brown, Gold320 ± 5% ΩRed, Blue, Green2 600 000 ± 20% Ω

Front 32

9.1

Voltage and Current in Circuits

Back 32

The voltage in a circuit must always be consumed before returning to the source.The sum of the voltage lost on the loads of the circuit will equal the total voltage of the source.The current in a circuit must always be accounted for and will never disappear or be consumed.Current in a circuit is similar to water flowing through pipes.

Front 33

Series Circuits

Back 33

There is only one path for current to travel.Since there is only one path for the electrons in a series circuit, the current in each part is equal.Current must pass through all loads in the circuit.

Front 34

Series Circuits

Back 34

The voltage is shared by all loads in the circuit and be used up before returning to the source.Each load in a series circuit uses a portion of the total voltage.When a load or resistor is added in series, the overall resistance of the circuit increases.

Front 35

Parallel Circuits

Back 35

There are multiple paths for current to travel.Current will split as some electrons go each way.When the pathways re-join, so does the current.The sum of the current in the pathways must equal the overall current in the circuit.

Front 36

Parallel Circuits

Back 36

When the electrons cycle through the circuit they must choose only one path.The voltage drop at each load is equal to the voltage supplied by the source.When a load or resistor is added in parallel, the overall resistance of the circuit decreases.

Front 37

9.2

Power

Back 37

Power is the rate of change in energy, also known as the rate at which work is done.The unit of measurement for power is the watt (W).Power, current and voltage are related using a mathematical equation:Power (P) = Current (I) x Voltage (V)

Front 38

Energy

Back 38

Energy is the ability to do work.The unit of measurement for energy is the joule (J).An equation can be used to relate energy (joules) with power (watts) and time (seconds):Energy (E) = Power (P) x Time (t)

Front 39

Relationship Between Energy and Power

Back 39

Power (watts) is measured as units of energy (joules) per unit of time (seconds).Electrical power is the rate of change in electrical energy.Eg. A 25 W fluorescent bulb converts 25 joules per second of electrical energy into light energy.

Front 40

Relationship Between Energy and Power

Back 40

If the voltage and current flowing through a device are known, the power of the device can be calculated.The amount of time the device is in use, along with the power will determine how much energy it consumes.

Front 41

Energy on a Large Scale

Back 41

A joule is a very small amount of energy.Energy consumption in homes is often measured using kilowatt•hours (kw•h).When using kilowatt•hours for energy, power and time must be in terms of kilowatts and hours, respectively.

Front 42

Paying for Power

Back 42

The power company can determine how many kilowatt•hours of energy have been consumed.Consumption is measured on an electric meter.

Front 43

Paying for Power

Back 43

the energy is then multiplied by the cost per kilowatt•hour.