Name: ____________________
SNC1
Static Electricity
1) a) In static electricity, the charges do not move.
b) Static electricity makes us feels strange, but it does not produce a painful shocks.
c) Current electricity (like the electricity from a wall socket) involves moving charges.
d) Current electricity causes painful shocks.
2) Like charges repel, unlike charges attract, charged objects attract uncharged ones.
Show where charges are in an atom
dark circles
small dots
light circles
3) In an atom: protons have a “+” charge
electrons have a “-” charge
neutrons have no charge.
protons can not easily be transferred from one object to another,
electrons can easily be transferred from one object to another.
4) In a solid:
5) Objects become charged when electrons are moved from one object to another.
6) a) All objects contain both positive and negative charges.
b) Positively charged objects have more positive than negative charges.
c) Negatively charged objects have fewer positive than negative charges.
7) For the following objects which are i) positively charged,
iii) neutral,
a
b
positive neutral
ii) negatively charged,
iv) not likely to occur naturally
c
d
e
f
g
negative unnatural positive unnatural positive
Charging by Friction
8) Why can we not charge to objects by touching them together, why must we rub them together?
It takes energy to remove electrons from atoms.
9) Show what will happen to the charges when the following objects are rubbed together.
a) balloon and hair
b) cotton shirt and
c) cotton towel and
wool socks
copper pipe
+
e- from hair to balloon
+
e- from sock to shirt
+ e- from towel to pipe
10) How do cars and aircraft get static charges? Rubbing against air and dust.
Charging by Contact
11) Static charges can be transferred from one object to another when they touch.
12) a) Show what happens to the charges when each of the following pairs of objects come in contact.
b) What charge does each object have i) before and ii) after they come in contact?
<—
o
-
<—
-
+
o
<—
o
+
+
Conductors and Insulators
13) a) Substances in which electrons can not move easily are called insulators.
b) Substances in which electrons can move easily are called conductors.
c) Substances in which electrons can move somewhat easily are called semiconductors.
List four household examples of each of the above.
o
+
14) A charge in placed on a rubber balloon and copper pipe by rubbing each with a piece of wool.
a) What charge will the balloon get? b) What charge will the pipe get?
c) What charge will the wool get? +
d) Show how the charges will move through balloon and the pipe.
- stay clustered - spread out
15) a) Which type of substance do we use to protect us from electric shocks? insulators
b) Which type of substance do we use to transport electric charges?
conductors
c) Which type of substance can build up large static charges?
insulators
16) Insulators, like air, can still conduct electricity if the charges are large enough. They are ionized.
An example of this around the house is a spark. An weather example is lightning.
When filling a gas tank, why must the gas nozzle be kept in contact with the gas tank?
To keep the tank grounded so static charges cannot build up and cause a spark.
17) Why do ships not build up static electric charges the way that cars and aircraft do?
Water usually has enough dissolved ions to conduct the static charges away.
Charging by Induction
18) When a charged object is brought near a neutral conductor, the charged object will push electrons in the
neutral conductor around. This will make one part of the neutral object positive and the opposite end negative.
The two objects do not touch in this type of charging.
19) Show with arrows what will happen to the electrons in the metal plate when the positive rod is brought
close to it. Show which side of the metal plate will be negative and which side will be positive.
- —>
positive
negative
Discharging
20) a) What does it mean to be discharged (use the term excess charge)? charge ratio becomes 1:1
b) How is discharging in a positive object different from discharging in a negative object?
e- donated to another object (if negative) versus electrons taken from another object (if positive)
21) a) Is the earth a good conductor, a good insulator, or somewhere in between? in between
b) Which contains more atoms, the earth, or an object like a car, person, or house? the earth
c) Why does contact with the earth cause objects to discharge?
e- can be added to or taken from the earth without causing a significant change in its charge ratio.
22) Why do excess electrons leave objects at pointed tips? They are pushed the e- behind the tip.
Why does this not work at a rounded surface? e- are all at the surface and can only push sideways.
23) Why does humid air cause objects to be discharged? Water molecules are good charge carriers.
24) Summarize the three ways that you could cause an object to be discharged.
a) grounding b) point discharge
c) humidity
25) a)Why does static electricity build up more in the winter than the summer? Less humidity.
b) Why do aircraft need discharge tips? They are insulated from the earth and rub against air and dust.
c) How do cars get rid of their static build-up? Their tires conduct electricity and keep them grounded.
26) a) What would happen to the metal bar if the positive rod was brought close while the metal bar is grounded
(electrically connected to the earth)?
e- would be drawn through the ground wire from the earth into the metal bar.
b) If the connection to the earth was broken before the rod was taken away, what would be the result?
The electrons would be trapped in the bar giving it a negative charge.
c) Would it be permanent? Yes.
d) This is an example of charging by induction.
27) a) Electrons will be attracted up from the leaves to the top of the electroscope.
The leaves will become positive and spread apart.
b) Electrons will be repelled down from the the top of the electroscope into the leaves.
The leaves will become negative and spread apart.
c) Electrons will be attracted up from the leaves to the top of the electroscope.
The leaves will become less negative as this takes place and will move together.
If the leaves become positive, they will subsequently spread apart again.
d) Electrons will be attracted up from the leaves to the top of the electroscope.
The leaves will become more positive and spread farther apart.
28) Summarize one practical use of static electricity.
i) Statically charged pollution particles can be removed from power plant exhaust.
ii) Statically charged spray paint will more efficiently paint an object that has the opposite charge.
iii) In a photocopier, static charges are used to paint a picture onto a piece of paper then opposite
charged plastic dust will stick to those parts of the paper.
29) Outline the steps that take place to produce lightning in a cloud.
i) updrafts and down drafts (wind currents) cause dust and ice crystals to rub and charge by friction.
ii) these charged particles collect in the top (usually +) and bottom (usually -) of the cloud.
iii) the negative charge at the base of the cloud causes the ground to become + by induction (electrons
in the ground are repelled by the negative part of the cloud.
iv) air molecules are pulled apart (ionized) by the opposite charges in the cloud and the ground.
v) these channels of ionized air allow electrons to flow from the cloud to the ground: lightning.
this process starts at the ground level, so the flash of lightning progresses upwards.
30) a) List 3 things that you should NOT do during a thunderstorm.
talk on a land line phone
take a bath or shower
wash dishes (or come into contact with any metal connected to the outside of the house)
stand in open spaces
stand under a tree
b) List 3 things that you should do in a thunderstorm.
get into a building or a car
unplug any sensitive electronics that are not on surge protected electrical circuits
crouch down on the balls of your feet if you start feeling statically charged