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Lab pages 270­271
1. A ­ was attracted to the wall
B and C ­ not attracted ­ fell or tried to flip to A
2. Both comb and fur pick up pieces of paper
3. The water is attracted to the polyethylene
4. The water should be attracted to the acetate as well
6. The 2 polyethylene strips repel
7. The charged and uncharged ends attract
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8. The acetate should have the same results as the polyethylene
9. The acetate and polyethylene attract
10. a) static charges do not move
b) attract
c) as the distance decreases the force increases
d) not all things repel when charged, some attract
e) like charges repel; unlike charges attract Nov 30­9:03 PM
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f) To determine if an object is charged or not and, if charged what the charge is, you must observe the object being repelled by an object of known charge. Charged objects will attract unlike charges and uncharged objects but will only repel objects of the same charge.
g) ­ there are 2 types of charges ­ negative and positive and also uncharged
­ the closer the objects are the stronger the force
­ charged objects attract uncharged objects
­ objects become charged when different substances are rubbed together Nov 30­9:03 PM
Electrical Nature of Matter
pages 272­273
1. a) Static means that it is not moving. It is used to describe the behaviour of electric charges on some objects because the charges tend to stay in the same place on the object.
b) When we put the balloon on the wall at the spot where it was rubbed against the hair it stuck but when it was turned around to the part that was not rubbed it did not stick.
2. The law of electric charges states that like charges repel and unlike charges attract.
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2. b) ­ rub polyethylene strip and fur and put on stirrup
­ rub a second polyethylene strip with fur and put near the first one. They will repel because they are like charges
­ rub acetate with silk and bring near the polyethylene. They will attract because they are opposite.
c) Attraction can happen if the objects have the opposite charge or if one object is charged and the other object is uncharged.
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3. ­ charges will stay on one spot on an object
­ 2 kinds of charges ­ positive and negative
­ force between objects increases as the distance decreases
­ like charges repel and unlike charges attract
­ charged objects attract neutral (uncharged) objects
­ charges apply to all substances ­ solid, liquid or gas
4.
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5. a) The photocopier creates static charges. Sometimes these go onto the paper and cause them to be attracted to one another.
b) ­ remove the charge by rubbing your hand over the sheets ­ increase the humidity in the air
6. a) Uncharged objects are attracted toward charged objects (depending on the size of the objects)
b) ­ uncharged dust particles to a charged TV screen
­ charged balloon to an uncharged wall
­ uncharged water to a charged comb
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Charging by Friction
pages 274­275
1. a) same diagrams as in book (Figure 1)
As the two objects are rubbed together the electrons move from one object to the other. The one that loses the electrons becomes positively charged and the one that gains the electrons becomes negatively charged.
b) ­ what the 2 objects are ­ The farther apart the 2 materials are on the electrostatic series the more static charge is built up.
­ how much you rub them together ­ this controls how many molecules come in contact with each other
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2. You find the 2 materials on the chart. The one that is higher to the top will become positively charged and the one that is farther down will become negatively charged.
3. a) i) acetate will be positive and fur will be negative. ii) rubber will be negative and the cotton will be postive
b) i) acetate will give up electrons to the fur so it will become positively charged and the fur will have picked up more negative charges so it will become negatively charged Nov 30­8:57 PM
3. b) ii) The cotton will give up electrons to the rubber so it will become positively charged (it has more protons now than electrons) and the rubber will become negatively charged because it has picked up more electrons.
4. The silk blouse will have a negative charge because the wool (which is higher on the electrostatic series) gives away its negative electrons to the silk.
An antistatic product will coat the materials with the same material and the objects appear to have the same charge. The electrons do not move around to or from the objects.
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5. Aluminum combs are better in the winter because aluminum is closer to human hair on the electrostatic series so there is a weaker attraction between hair and aluminum than between hair and plastic.
6. It causes a series of flashes of light because the rapid movement of the feet sometimes makes enough electric charge to produce a series of tiny sparks that light up the space beneath the sheets. Nov 30­8:57 PM
Charging Different Substances by Contact (p.276­277)
1. The pith ball was attracted to the negatively charged polyethylene strip.
2. The pith ball was attracted to the positively charged acetate strip.
3. The pith ball was attracted to the negatively charged polyethylene strip. After a second it repelled away from the strip. When the positively charged acetate strip was brought close to the pith ball it was attracted to the strip.
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4. The pith ball was attracted to the positively charged acetate strip. After a second it repelled away from the strip. When the negatively charged polyethylene strip was brought close to the pith ball it was attracted to the strip.
6. When the negatively charged polyethylene strip was touched against the iron rod the pith ball repelled from the end of the rod.
7.The negatively charged polyethylene strip repelled the pith ball.
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8. When the negatively charged polyethylene strip was touched against the glass rod the pith ball did nothing. The recharged polyethylene strip attracted the pith ball.
9. a) When brought near but does not touch there is no charge transferred to the pith ball. This is so because it is attracted to both positive and negative strips.
b) i) Negative charges are transferred to pith ball because after being charged by contact the pith ball repels from the negatively charged object.
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b) ii) Negative charges are transferred from the pith ball because after being charged by contact the pith ball repels from the positively charged object.
c) An object that has been charged by contact always receives the same kind of charge as that on the object giving the charge.
d) negative
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e) When the negative charged polyethylene strip touched the end of the iron rod some of the excess electrons transferred from the strip to the rod. These added electrons repelled other electrons in the rod along its length so the electrons on the other end transferred to the pith ball. The negative charged pith ball then repelled from the negative charged iron rod.
f) no charge
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g) When the negative charged polyethylene strip touched the end of the glass rod some of the excess electrons transferred from the strip to the rod. These added electrons remain in the same position and do not cause the movement of electrons along the rod so no charge unto the
pith ball.
h) Iron is a substance in which electrons can move freely from one atom to another. Glass is a substance in which electrons cannot move freely from one atom to another.
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1. Negative charges move from your hand to the doorknob. Negative charges are transferred from the wool to the cotton by friction. When your hand touches the doorknob the negative charges transfer from your hand to the neutral doorknob charging it negatively by contact.
2. a) Like charges repel.
b) Unlike charges attract.
c) Neutral objects are attracted to charged objects.
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Page 279 Transferring Charge by Contact
2. the object has the same charge as the object giving the charge. The electrons will move from the object that has more electrons to the object that has less electrons.
3. The electrons jump across the air gap between one object to another. Moving your hand fast will not prevent this.
4. cat ­ positive ­ fur is higher on the electrostatic ebonite ­ negative series
the person touching the cat would get a positive charge
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Page 280­281
Insulators and Conductors
1. An electrical insulator is a substance in which electrons cannot move freely from atom to atom.
As wood and glass surfaces are cleaned there is a continuous buildup of static charges. The electric charges remain on the surface and attract uncharged dust particles.
The surface of a car can build up very large amounts of charge due to the air rushing over it. When you get out of the car after a trip you could get a shock.
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2. Because electrons can not be conducted through electrical insulators, these materials can protect us from electric shocks. The 2 wires carrying the electric current to an electric kettle would be very dangerous if they were not covered with a plastic substance.
3. An electrical conductor is a substance in which electrons can move freely from one atom to another.
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4. In winter the cold air is much drier and contains fewer water molecules than in other seasons. Dry air is an insulator and does not pick up charges from our body as the air molecules collide against us. In winter static builds up on our clothes and tends to stay. This could be reduced by adding moisture to the air.
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Discharging Electrically Charged Objects (282­283)
1. Discharged is when all the excess electric charges are removed from a charged object.
2. The simplest way of discharging an object is to connect it to the Earth itself by means of a conductor. This is called grounding.
When a charged object is connected to Earth it shares its charge with the entire Earth. The damp soil is a fairly good conductor and the Earth is a lot larger so it takes in the charge. An example is gas pump where it and everything attached to it are grounded. Another example is people working assembling electronic equipment who wear a metal strap on one of their wrists. This is attached to a grounding system.
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3. The surface shape of an object affects the rate at which it becomes discharged . Smooth, spherical shapes retain charges indefinitely because the charges spread themselves evenly over the surface.
4. Discharge at a point is a method of discharging where the electrons are pushed off the point at the tip of the object in a continuous stream.
5. Static wicks ­ pointed metal rods that stick out from the movable control surfaces in the wings and tail. These allow for the discharge from a point.
Inflatable rubber covering ­ covers edge of wing. This allows the electricity to leak out.
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6. The rubbing action of the hat on your hair would produce static charge on the toque and your hair because of their position on the electrostatic series.
7. Two other ways to discharge are to shine a light on it or exposes it to radioactivity.
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