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Charging by Friction,
Contact and Induction
SNC 1P
Agenda1. Charging by Friction2. Take up lab from Thursday3. Charging by contact4. Charging by Induction5. Discharging an Object 6. Lightning
Lesson Learning GoalsBy the end of today’s lesson you will;
● Understand the difference between charging by friction, contact and induction.
● Understand how to discharge objects● Understand why lightning happens.
What is Friction?● Friction is the resistance that
happens when we rub two things together
● To create static electric charges using friction all we have to do is rub two different materials together
● When two different materials are rubbed together one of them will take electrons from the other.
● The materials that gains electrons becomes negatively charged
● The material that loses electrons becomes positively charged.
Electronegativity● Refers to how strongly the atoms of a substance pull on
electrons● An object with a higher electronegativity will take
electrons from the other● The greater the difference in their strengths, the greater
the static charge that will be created.
The Triboelectric Series● The triboelectric series is a chart that
shows different materials and their tendency to gain or lose electrons.
● When two materials are rubbed together you can use this chart to determine which materials will become positive and whith will become negative.
● Whichever one of the two materials is higher on the chart will lose electrons and become positive.
● The one that is lower will gain electrons and become negative.
Example:
● What happens if we rub an ebonite rod and cat fur together? Which one becomes positive and which one becomes negative?
Answer● The ebonite rod would gain electrons and become negatively charged.● The cat fur would lose electrons and become positively charged.
Negative Positive
● These 2 objects would now be attracted to each other because of the laws of electric charges (opposites attract).
Take up Lab
Charging by Contact
Charging by Contact-
Positively (Using a Positively
Charged Rod)
● When charging by contact, a charged rod is touched to a neutral object (in this case, a metal leaf electroscope).
● Electrons will transfer between the charged rod and the neutral object. This transfer of charges places a new charge on the neutral object.
● The neutral object will take the same charge as was on the charging rod.
Charging by Contact (with a positively charged rod)● This electroscope is neutral. There are equal
numbers of protons (+) and electrons (-) evenly distributed over the electroscope.
● You can tell the electroscope is neutral because the leaves are hanging straight down
● When a positively charged rod is brought near to the head of the electroscope, the electrons on the electroscope are attracted by the strong positive charge, and shift upward to be close to the rod.
● The leaves at the bottom of the electroscope now are positively charged and since like charges repel, the leaves move apart from each other.
● When the positive rod touches the head of the electroscope, electrons from the electroscope transfer onto the positive rod.
● When the electroscope loses electrons it becomes positively charged.
● The leaves of the electroscope repel.
● Since the electroscope has lost electrons, it now has a positive charge.
Charging by Contact (with a negatively charged rod)● This electroscope is neutral.
There are equal numbers of protons (+) and electrons (-) evenly distributed over the electroscope.
● You can tell the electroscope is neutral because the leaves are hanging straight down.
● When a negatively charged rod is brought near the head of the electroscope, the electrons on the electroscope are repelled by the strong negative charge, and shift downward to the leaves to get away from the rod.
● The leaves at the bottom of the electroscope now are negatively charged and since like charges repel, the leaves move away from each other.
● When the negatively charged rod touches the head of the electroscope, electrons from the rod transfer onto the electroscope.
● When the electroscope gains electrons, it becomes negatively charged,
● The leaves of the electroscope repel.
● Since the electroscope has gained electrons, it now has a negative charge.
Charging by Induction
Induction● Induction happens when charges move around in an object but DO NOT leave
or arrive.● The overall charge of an object stays neutral but the charges move to create
charged areas● This happens by bringing a charged object near a neutral one and
repelling/attracting the electrons● This results in induced charge separation.
Charging by Induction● A charged rod causes the electrons
in the electroscope to get closer/farther away from the rod depending on the charge of the rod.
● This will create a charge in the leaves of an electroscope and they will repel.
Grounding
● Charging by induction is temporary but can be made permanent using grounding.
● You can use a conductor to carry charges away from an object safely and guide them towards earth (a huge conductor)
Discharging Objects
● Discharging means getting rid of the excess charges on an object.● With a small charge, like a static build-up on us during the winter, we
can simply touch something larger to discharge ourselves.● When large charges build-up on objects, the safest way is to attach
them to the ground by a wire.
Lightning Rods
● Are used to attract lightning away from sensitive structures.
● They are attached to taller buildings and made of good conducting material in the hopes that electrons will pick the lightning rod as the path of least resistance.
● The rods are grounded, allowing large amounts of electrons a place to discharge safely.
Lightening● Lightning is a very common example of an electrical discharge.● A buildup of charges in the clouds finds a pathway to the ground, and the
electrons discharge in a bright spark that we call lightning.● The thunder sound is due to the superheating of the air around the lightning
to thousands of degrees.
● When clouds form, the rising water molecules sometimes lose electrons that fall off near the bottom of the cloud
● This makes the bottom of the cloud have a partial negative charge and the top of the cloud have a partial positive cloud.
● The negative charge in the bottom of the cloud causes inducing charge separation in the ground where the negative charges will move deeper and positive will stay near the surface
● The negative charges in the bottom of the cloud are strongly attracted to the positive charges at the top of the earth.
● The electrons start seeking out the path of least resistance and electron tendrils begin creeping down from the cloud
● When the electrons find the easiest path, they complete a pathway to the positively charged ground and the electrons travel through this path.
● The electrons will rapidly discharge from the cloud to the ground. The energy released causes the big spark and also the loud crack we call thunder
Hom
ewor
k: ● Pg. 261 # 2, 4, 6● Pg. 267 # 1, 2● Pg. 273 # 2, 3, 8
