2016-17 Electricity 1
II
1.
III
From the diagram at the left.
A. ___ A proton
B. ___ An electron
C.
D.
___ A neutron
___ The nucleus
I
IV
2.
Which of the subatomic particles in the atom is easily removed?
3.
So, when charges move it is almost always the ____________ that are moving.
Protons and neutrons are held together in the nucleus of atoms with the “Strong Nuclear Force”, the strongest force in nature. Without it protons couldn’t be together in the nucleus. It is very difficult to remove a proton from the atom. Electrons,
on the other hand, move more easily and very easily in metals, called conductors. The moving of electrons in conductors is
called electricity. When an object has a + or − charge it is because electrons have moved, not protons.
4.
5.
Opposites attract and like charges repel.
A) Two protons will:
B) Two electrons will:
C) An electron and a proton will:
For each of the
pairs of charges,
will they attract
or repel each other:
A)
+
+
Attract or Repel?
B)
–
+
Attract or Repel?
C)
–
–
Attract or Repel?
− − − − − −
R
?
S
6.
At the left, a particle is shot between the charged plates of a capacitor. The path
the particle will take depends on its charge. Determine the charge for each path.
A. If path R:
B. If path S:
C. If path T:
7.
For the three spheres shown below, count up the number of +s and − and decide
if the net charge of the sphere is positive (+), negative (−), or neutral (0).
T
+
9.
+
–
–
+– +
A) ____
+ + + + + +
8.
–
B) ___
–
–+ –+
– – –
+ +
– –
C) ____
–
+
–
+
+
+
For the next four examples decide the net charge of the object. (A proton is a +1. An electron is a −1.)
D)
___ An object with 2 protons and 4 electrons
F)
___ An object that loses electrons.
E)
___ An object with 18 protons and 16 electrons
G)
___ An object that gains electrons.
A piece of rabbit fur is rubbed against a rubber rod. The rubber rod becomes negative. Did the rubber rod gain or
lose electrons?
10. A. So, how do objects become positive?
Electric Charge
The unit of charge is a fundamental quantity.
Electron Charge
-19
1 electron = - 1.6 × 10 C
The smallest unit of charge is a
proton or an electron. You cannot
have part of an electron, because it
would lose its negative charge.
Therefore, you cannot have less
than -1.602 x 10-19C of charge and
any amount of charge must be multiples of this number. You can
have 12 electrons or 13 electrons,
but not 12.5 electrons!
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B. How do objects become negative?
The charge of a proton is the same
as an electron, only positive:
1 proton = +1.602x10-19C.
1e
1e
½e
−
−
−
Not
possible
Electric charge is quantized,
meaning the amount of
charge must always be in
multiples of e. You can never
have part of an electron.
Ex: What is the charge of an object that
gains 1.2 x 108 electrons?
Do a conversion :
 1.2 × 108e  −1.6 × 10 −19 C 
−11


 = −1.92 × 10 C
1
1e



Ex: How many electrons are gained or lost if an object
has a charge of 4.6µC (microcoloumbs)?
 4.6 × 10-6 C

1


1e

−13

 = −2.87 × 10 e
−19
  −1.6 × 10 C 
The negative means it lost e’s (a + object).
Copyright © 2017, C. Stephen Murray
2016-17 Electricity 1—p2
11. A. Can an object gain 6.5 electrons?
B. Why or why not?
Remember conversions? If set up correctly the units cancel. See the two examples on the front page.
12. How much charge do 15 electrons have?
13. An object has a charge of –4.5×10−6 C. How many electrons did it gain?
Ex: A 2µC charge is 3 mm from a 6µC charge.
What is the electric force between them?
Coulomb’s Law
Charge 1
(in Coulombs)
Electric
Force
(in N)
Fe = k c
Coulomb’s Constant
= 9 ×109 Nm2/C2
Charge 2
(in C)
q1q2
r2
Variables:
Distance
between
the two
charges
(in m)
kc = 9×109
q1 = 2×10-6C
q2 = 6×10-6C
r = 3×10-3m
The Coulomb’s force is known as the Electrostatics Force. It is
actually a part of the Electromagnetic Force, which is also one
of the Four Fundamental Forces of nature.
q 1q 2
r2
(2 × 10 −6 )(6 × 10 −6 )
= 9 × 109
(3 × 10 −3 ) 2
Fe = k c
= 9 × 10 9
1.2 × 10 −11
= 1.2 × 10 4 N
9 × 10 −6
Since they are like charges: they repel.
The Four Fundamental Forces:
1.
The Strong Nuclear Force: The strongest force in nature, but very short-ranged (in distance). Only acting between protons
and neutrons, it hold the nucleus together. Neutrons provide strong nuclear force, but no repulsion.
2.
The Weak Nuclear Force: Stronger than gravity, but only over very short distances (10−18 m). Allows fusion in the sun. Is
responsible for beta decay in unstable atoms. (Beta decay is where a neutron decays into a proton and an electron, the
“beta” particle.)
3.
The Electromagnetic Force: Responsible for electricity, binding of atoms into molecules, and most every day contact forces.
Decreases with distance as 1/r². Electricity can make magnetism, thus the “electromagnetic” force.
4.
The Gravitational Force: Weakest force in nature, but responsible for holding together solar systems and galaxies. A long
range force that decreases as 1/r², like the electromagnetic force. All objects, even electrons and protons, feel gravitational
forces from every other object, but gravity is much weaker than the other forces, so can sometimes be neglected.
14. Using the example above, calculate the force between a 6 C and a 4C charge that are 8 cm apart (remember to use meters and
the “EE” key).
S
Since the electricity and magnetism are linked, let’s talk some magnets.
15. Magnets have two sides called: __________.
N
16. Instead of positive and negative they are called: __________ and __________.
17. In the diagram at the right, the two magnets are attracted to each other. Label the blanks on the
lower magnet.
18. Two circular magnets are placed on a table next to each other.
A. Attract or repel?
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___
___
B. Attract or repel?
Copyright © 2017, C. Stephen Murray
cstephenmurray.com
Copyright © 2017, C. Stephen Murray
cstephenmurray.com
Copyright © 2017, C. Stephen Murray