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Science second semester test study guide

Weathering

Mechanical weathering is the breakdown of rock into smaller pieces by mechanical means.  Agents include ice, wind, water, gravity, plants, and animals.

 

Chemical weathering is the process by which rocks break down as a result of chemical reactions.  Agents include water, weak acids, and air.

 

 Soil is a loose mixture of small mineral fragments, organic material, water and air that can support the growth of vegetation.

 

 A soil’s ability to hold and supply nutrients to a plant is described as fertility.  The organic material formed in soil from the decayed remains of plants and animals is called humus.

 

 Soil often ends up in a series of layers with rich soil on top, sediment below that, and bedrock on the bottom.  These layers are called horizons.

 

The  pH scale is used to measure how acidic or basic a soil is and ranges from 0 to 14.   Soil that has a pH below 7 is acidic, while soil that has a pH above 7 is basic.

 

The Nature of Waves

Any disturbance that transmits energy through matter or empty space is a wave.

 

 A medium is a substance through which a wave can travel.  This substance can be a solid, liquid, or gas.

 

 A mechanical wave is one that requires a medium to travel.  Sound, seismic, and water waves are mechanical waves and therefore require a medium.

 

 A transverse wave has particles that vibrate perpendicular to the direction the wave is going.  The highest point of a transverse wave is called a crest.  The lowest point of a transverse wave is called a trough.

 

A longitudinal wave has particles that vibrate back and forth along the path that the wave.  The part of the wave where the particles are crowded together is a compression.  The part of the wave where the particles are stretched apart is called a rarefaction.

 

The height of a wave, or the maximum distance that the particles of a wave vibrate from their rest position, is known as amplitude.  The distance from any point on a wave to an identical point on the next wave is known as wavelength.  The number of waves produced in a given amount of time is known as wave frequency.

 

Sound

A vibration is a complete back and forth motion of an object.  How high or low a sound is perceived to be is the pitch of that sound.  Frequency is expressed using the unit hertz (Hz).   Loudness is expressed using the unit decibels (dB).

 The more dense the medium is, the faster sound can travel through it.  Therefore sound travels quickly through air, but it travels faster in water and even faster in solids.  Temperature also affects the speed of sound travel. The cooler the medium is, the slower the speed of sound or the warmer the medium is, the faster the speed of sound.

 

 An observed change in the frequency of a wave when the source or observer is 

 moving is the Doppler Effect.  Due to the pressing together of compressions and rarefactions, the pitch of  a car is approaching a listener will rise whereas the pitch will drop as the car moves away due to the stretching out of the compressions and rarefactions.

 

The bouncing back or reflection of a sound wave is also known as an echo.  The process of using reflected sound waves to find objects is known as echolocation.

 

The electromagnetic spectrum 

All electromagnetic waves travel at the speed of light:  300,000 km/sec or 186,000 miles/sec.

 

Radio waves have some of the longest wavelengths and lowest frequencies of all EM waves.  Television and radios are examples of devices using radio waves.

 

Microwaves have shorter wavelengths and higher frequencies than radio waves do.   Uses include microwave ovens, cell phones, and radar.

 

Infrared waves have shorter wavelengths and higher frequencies than microwaves do.  Anything producing heat gives off infrared waves.

 

Visible light waves have shorter wavelengths and  higher frequencies than infrared waves do.  This section is the only section of the electromagnetic spectrum that humans can see.  Be sure to know the colors in order of increasing frequency (Roy G. Biv).

 

Ultraviolet light has shorter wave lengths and higher frequencies than visible light does.  The sun is the primary source of ultraviolet light although the ozone layer blocks much of it out.  Negative effects of UV light include wrinkles, eye damage, skin cancer, and sunburn.  Positive effects are vitamin D production by the skin and the ability to kill bacteria on food and surgical tools.                                        

X-rays have shorter wavelengths and higher frequencies than UV  radiation.  Uses of x-rays include seeing structures inside the human body and the use of security devices at airports and federal buildings.

 

Gamma rays have the shortest wavelengths and highest frequencies of all electromagnetic waves.   Uses include the treatment of cancer, to produce nuclear energy, and to kill bacteria in foods.

 

Atoms and electricity:  The study guide for electricity will not be reprinted as you should still have it.  If it has been misplaced, you may download and print another copy from Ms. Voss’ website:    http://vossscience.educatorpages.com/

 

 

 

 

Electricity test study guide – do not lose!  You will need this for final exam!!

 

Section 1:   Electric charge and static electricity

Atoms – The nucleus of the atom contains protons which have a positive charge and neutrons which have a neutral charge.  The nucleus is orbited by negative charged particles called electrons.  Atoms that have a positive charge have lost electrons, while atoms with a negative charge have gained electrons.

 

The law of electric charges states that like charges such as positive/positive and negative/negative charges repel each other while opposite charges, such as positive and negative attract each other. 

Objects can be charged in three ways:

friction – electrons are “wiped” from one object to another such as a balloon on hair.

conduction – electrons move from one object to another by direct contact such as touching an uncharged piece of metal with a positively charged glass rod.  The electrons flow from the metal to the rod which becomes negatively charged.

induction – occurs when charges in an uncharged metal object are rearranged without direct contact with a charged object.  Recall how the foil strips reacted in the electroscopes before the balloon touched the paper clip.

 

An electrical conductor is a material in which charges can move easily.  Metals that make good conductors include copper, mercury, and aluminum. 

Electrical insulators are materials in which charges can not flow easily because these materials hold onto their electrons.  Materials that make up insulators include plastic, rubber, glass, wood, and air.

 

Static electricity is the electric charge at rest on an object.   Electric discharge is the loss of static electricity as it moves off an object.  Lightning is an example of electric discharge.

 

Section 2:  Electric current and electrical energy

 

Electric current is the rate at which charges pass a given point.  The higher the number is, the greater the number of charges that pass the point each second. 

 

Units to know:                                                            Symbol

- electric current is expressed in amperes or amps                          A

- in an equation the symbol for current is:                                        I

- voltage                                                                                            V

- resistance                                                                                        R

 

Direct current (DC) – is when the electrical charges in a current travel in one direction only!  Typically this is with a battery and the charges flow from the energy source, the battery, towards the load.

Alternating current (AC) - the electrical current charges continually shift from flowing in one direction to flowing in the reverse direction.  This is the type of electricity in homes or businesses.  In the United States, the alternating current changes directions 120 times /second or 60 cycles/ second.

 

Voltage is the potential difference between two points in a circuit.  Voltage is a measure of how much work is needed to move a charge between two points.  The size of the current depends on the voltage.  The greater the voltage is, the greater the current is.  Large voltage is needed for a large current, so the voltage in a car battery is 12 volts as compared with the 1.5 volts in AA or C batteries.

 

Resistance is the opposition to the flow of electric charge.  Good conductors such as copper have low resistance and poor conductors such as iron have high resistance.  Insulators have such high resistance that electric charges cannot flow through them.  The higher the resistance of a material is, the lower the current in the material is. * So if the voltage doesn’t change, as resistance goes up, current goes down.  An object’s resistance depends on four things:  the object’s      1) material           2) thickness          3) length            4) temperature

 

Section 4: Electric circuits

 

An electric circuit has three parts:

1.  Energy source:  This can be a battery (DC) or a power plant that provides AC.  Examples of energy sources are:  solar, wind, geothermal, hydroelectric, nuclear, or fossil fuel

2.  Wires: These are usually copper because it is a good conductor and has low resistance. 

3.  Load:  Loads change electrical energy into other forms of energy.  Examples are thermal, light and mechanical.  Examples of loads are appliances:  radios, light bulbs, microwaves, blenders, televisions, dishwashers, etc.

 

For charges to flow through a circuit, it must be closed so the charges can flow in a loop.  If a circuit is broken or open, charges cease to flow.  Switches allow us to open and close circuits to turn our electrical devices on and off.

 

A series circuit is one in which all parts are connected in a single loop.  There is only one path for the charges to follow, so the charges must flow through every part of the circuit.  If there is any break in a series circuit, the charges stop flowing.  None of the loads on the circuit will work.  This would not work in a house circuit, but works well in burglar alarms.

 

In parallel circuits, the loads are connected side by side.  Charges in a parallel circuit have more than one path on which they can travel.  If one load is broken or missing, charges still run through the other branches so the loads on those branches keep working.  This is the type used in homes and businesses.

 

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