Rub a balloon against your hair What can
Rub a balloon against your hair… What can you remember from G 10?
� Charge is a property of objects that causes them to be attracted to or repelled by other objects with charge. � Charge comes in two varieties �Negative �Positive � Protons carry positive charge � Electrons carry negative charge � Most macroscopic objects (table, book, banana, pencil) are uncharged as they have equal numbers of protons and electrons
� Structure of solids �Crystal lattice �Protons in nucleus; fixed and immovable �Electrons moveable in some materials �A positively charged object has lost electrons � A negatively charged objects has gained electrons
�A Fundamental conservation law � When one object rubs against another object, one object loses electrons, the other one gains the same number of electrons � Charge is never created or destroyed � Charge is always transferred in integer multiples of the elementary charge � Q=Ne
Charge (Q) is measured in coulombs (C) 1 C ~ 6. 25 x 1018 e Smallest possible amount of charge: 1 extra electron: q = -1. 60 x 10 -19 C 1 missing electron: q = +1. 60 x 10 -19 C For any charge q: =e = elementary charge … q = ne , where n = 1, 2, 3, etc… Charge is quantized Charge is conserved
The coulomb (selected for use with electric currents) is actually a very large unit for static electricity. It is common to use the metric prefixes. 1 m. C = 1 x 10 -6 C 1 n. C = 1 x 10 -9 C 1 p. C = 1 x 10 -12 C
- - ++++ glass silk - (rub) - ---- plastic Charging by Contact (rubbing…) fur (rub)
A material on the bottom of the list will gain electrons from a material above it on the list…
�A piece of fur is rubbed on an acrylic rod. If the rod gains a net charge of -3 n. C, how many electrons were transferred from the fur to the rod?
�A solid sphere has a net charge of – 4 n. C. How many electrons must be added or removed for the sphere to have a net charge of +5 n. C?
Electric Force RULE’s! Like charges repel each other. + - Force of repulsion + - Unlike charges attract each other. - + Force of attraction Electric Force = Non-contact force
Opposites Charges Attract Like Charges Repel
Conductors (such as metals, tap or salt water, and the human body) are good at conducting away any extra charge. Metal: “free electrons” Touching it with your hand will discharge it Insulators (like plastic, rubber, pure water, and glass) will not conduct away extra charge. Use rubber gloves in the lab
Charging by Contact Some electrons leave rod and spread over sphere.
Laboratory devices used to study the existence of two kinds of electric charge. Pith-ball Electroscope Gold-leaf Electroscope
1. Charge the rubber rod by rubbing against fur. 2. Transfer electrons from rod to each pith ball. The two negative charges repel each other.
1. Charge the glass rod by rubbing against silk. 2. Touch balls with rod. Free electrons on the balls move to fill vacancies on the cloth, leaving each of the balls with a deficiency. (Positively charged. ) The two positive charges repel each other.
Rubber glass Attraction fur silk Note that the negatively charged (green) ball is attracted to the positively charged (red) ball. Opposite Charges Attract!
Charging by Induction Rod does not touch sphere. It pushes electrons out of the back side of the sphere and down the wire to ground. The ground wire is disconnected to prevent the return of the electrons from ground, then the rod is removed.
The law of conservation of electric charge: "The net amount of electric charge produced in any process is zero. " Another way of saying this is that in any process electric charge cannot be created or destroyed, however, it can be transferred from one object to another. Charged comb attracts neutral bits of paper. Charged comb attracts neutral water molecules.
Explain in 2 sentences
Grounding -Object is - + + - + discharged or “grounded” + -+ - - -+ - + The earth is a huge reservoir of positive and negative charge © Laura Fellman
Earthing Petrol Tankers Petrol rubbing against the pipe can build up a static charge which could cause an explosion The tanker is joined to the ground with a wire to stop a charge building up
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