unit 3- electricity ordinary matter is made up of atoms which have protons and electrons. the...
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Unit 3- Electricity
Ordinary matter is made up of atoms which have protons and electrons.
The magnitude of the charge on one proton or electron is called the elementary charge "e".
Charge is quantized as a multiple of the electron or proton charge:
proton charge: e=1.602 x 10-19 Coulombs electron charge: e=-1.602 x 10-19
Coulombs
One coulomb (C) of charge represents an excess or deficit of 6.24 x 1018 electrons.
Charge (Q) on an object is equal to the number of elementary charges on the object (N) multiplied by the elementary charge (e).
Q = Ne
Example 1:
How much charge does the capacitor hold if it has 4.5 billion elementary charges?
Solution:
Q= ?N = 4.5 x 109 elementary chargese = -1.602 x 10-19 Coulombs
Q = NeQ = 4.5 x 109 x -1.602 x 10-19
Q = -7.209 x 10-10
Example 2:
If an object has 4 coulombs of charge stored, how many elementary charges are present?
Solution:
N = ?Q = 4 Coulombse = -1.602 x 10-19 Coulombs
N = Q/e N = 4 / 1.602 x 10-19 [Note: you can
remove the - from the charge]N = 2.5 x 1019 electrons
Example 3
How many electrons must be removed from an charged pair of wool socks with a -1µC charge to give it a charge of +2.3 µC?
Solution:
Qi= -1µC (Excess electrons) Qf= +2.3µC (Deficit electrons) N = ?e = -1.602 x 10-19 Coulombs
Qt = Qf – Qi; Qt = +2.3µC - (-1µC)Qt = +2.3µC + 1µCQt = +3.3µC
N = Q/e N = 3.3 x 10-4 / -1.602 x 10-19
N = 2.05 x 1015 electrons
Fundamental Law of Electric Charge:1. Opposite electric charges attract
each other. 2. Similar electric charges repel each
other.3. Charged object attract some
neutral object. Clip at
http://www.saskschools.ca/curr_content/physics30/elect/lessoniii_2_1.html
Current Electricity
An electric charge in motion Consists of a swarm of moving
electrons When electrons move from one
location to another, they produce an electrical current
Electricity flows through wires as water flows through pipes
Units for current
I= Q/t (I= current(A), Q= charge(c),
t=time(s) Measured in Amperes (A) 1 ampere of current flows when 1
coulomb of charge moves by a point in 1 second (about 6.3 billion billion electrons per second)
1A= 1C/1S
Types of currents
Direct current (DC): involves the continous flow of electrons in the SAME direction
Alternating current (AC): involves periodic reversal in the direction of electron flow
Reading current
Current is read using an ammeter, it must be hooked directly into the current to make measurements
Example
Find the amount of current flowing through an electric meter if it takes 900 C of charge to toast 2 slices of bread in 1.5 mins?
Solution
I=Q/t
I= 900C/ 90s
I=10A
Assignment:
current and potential difference questions