2. 2
Electrostatics Assignment
KNOWLEDGE CHECK ON THE TOPIC
13 a. Draw an electric field for each of the particles following basic field drawing principles.
14. For each example below, show the direction of the magnetic field at each of the
designated points (*). If needed, you can use x dot into the page and a dot for out of the
page. Where possible, your vectors should also demonstrate appropriate field strength.
3. 3
15. An alpha particle (charge = 3.2*10^-19 C) is passing through parallel plates shown
below
a. In the image above, draw the electric field between the plate
The electric field between the plates is directed from the positive plate to the negative plate.
b. The electric field strengths is 3*10^6 N/C. Find the magnitude of the force on the
alpha particle.
The magnitude of the force on the alpha particle is given by F=qE, where q is the charge of the
alpha particle and E is the strength of the electric field. Substituting in the given values, we find
that
F = (3.2×10−19 C) (3×10^6 N/C)
4. 4
=9.6×106−13 N.
c. A magnetic field is created in the area between the plates such that the alpha particle
now travels in a straight line. What direction does the magnetic force need to be?
The magnetic force needs to be in the opposite direction of the electric force in order to cancel it
out and allow the alpha particle to travel in a straight line.
d. To achieve the magnetic force determined in (c), what direction must the magnetic field
be in?
The magnetic field must be in the same direction as the electric field in order to produce the
magnetic force in the opposite direction. The alpha particle will travel in a straight line because
the electric force and the magnetic force cancel each other out.
COMMUNICATE REASONING
16. An experiment is done where a glass rod is brought near to colored sequins (conductive
metallic disks) The sequins are lifted up by the glass rod. Three students discuss what this means:
Student 1: This must mean that the glass rod is positively charged and the sequins are negatively
charged
Student 2: Actually, we don’t know their charge, just that they are different. It is possible that the
glass rod is negative and the sequins positive.
Student 3: I think you are both wrong. The sequins could be neutrally charged. All we know is
that the rod is charged.
5. 5
Use excellent knowledge on charges to settle the argument. Tell us which student is correct (if
any) and justify your answer using the CER model (make a Claim, cite the Evidence, give
Reasoning)
ANSWER
Claim:
Student 1 is correct. The glass rod is positively charged and the sequins are negatively charged.
Evidence:
Opposite charges attract, while like charges repel. When the glass rod is brought near the
sequins, the sequins are attracted to the rod. This means that the sequins must have a
negative charge, since opposite charges attract.
Glass is a dielectric material, which means that it does not conduct electricity well. When
the glass rod is rubbed with a cloth, it becomes positively charged. This is because
electrons are transferred from the cloth to the rod. The sequins, being a conductor, are
able to take on the negative charge that was left on the cloth.
Reasoning:
The fact that the sequins are lifted up by the glass rod indicates that there is an attractive
force between the two objects. This can only be explained if the two objects have
opposite charges.
Since the glass rod has been rubbed with a silk cloth, we know that it has a net positive
charge. This means that the sequins must have a net negative charge in order to be
attracted to the glass rod.
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Student 2 is incorrect because they say that it is possible that the glass rod is negative and the
sequins positive. This is not possible because opposite charges attract. If the glass rod were
negative and the sequins positive, the two objects would repel each other.
Student 3 is incorrect because they say that the sequins could be neutrally charged. This is not
possible because the sequins are attracted to the glass rod. If the sequins were neutrally charged,
there would be no force between them and the glass rod.
In conclusion, Student 1 is correct. The glass rod is positively charged and the sequins are
negatively charged.
VERBAL DISCUSSIONS
17. Explain either how a generator creates current OR How current causes a motor to
work.
Note: You have a choice of which one to explain. A motor is easier to explain but “excelling”
can only be achieved by explaining the generator.
Explanation
A generator is a device that converts mechanical energy into electrical energy. It does this by
using a rotating magnet to induce an electric current in a coil of wire. The rotating magnet
creates a changing magnetic field, which in turn induces an electric current in the coil of wire.
The strength of the electric current is determined by the strength of the magnetic field and the
speed at which the magnet is rotating.
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The most common type of generator is an alternating current (AC) generator. AC generators
produce an electric current that changes direction many times per second. This is the type of
current that is used in homes and businesses.
Direct current (DC) generators also exist. DC generators produce an electric current that flows in
one direction only. DC generators are often used in cars and other vehicles. Here is a diagram of
a simple generator:
[Diagram of a simple generator]
The generator has a rotating magnet (1) that is surrounded by a coil of wire (2). When the magnet
rotates, it creates a changing magnetic field. This changing magnetic field induces an electric
current in the coil of wire. The electric current flows out of the generator through the output
terminals (3).
The speed at which the generator rotates determines the strength of the electric current. The
faster the generator rotates, the stronger the electric current. The strength of the magnetic field
also determines the strength of the electric current. The stronger the magnetic field, the stronger
the electric current. Generators are used to generate electricity in power plants. They are also
used in cars, trucks, and other vehicles to power the electrical systems.
18. Charge by Induction
Charge by induction is a process by which an electric charge is transferred to an object without
actually touching it. This can be done by creating a changing magnetic field near the object. The
changing magnetic field induces an electric current in the object, which in turn creates an electric
charge. Charge by induction is used in many different applications, such as electric motors and
generators. It is also used in some types of medical devices, such as MRI machines.
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Here is a more detailed explanation of how charge by induction works:
I. A magnet is placed near an object.
II. The magnet is moved towards or away from the object.
III. The movement of the magnet creates a changing magnetic field near the object.
IV. The changing magnetic field induces an electric current in the object.
V. The electric current creates an electric charge in the object.
VI. The amount of charge that is induced on the object is proportional to the strength of the
magnetic field and the rate of change of the magnetic field.
VII. Charge by induction is a very important process. It is used in many different applications,
and it is essential for the operation of many modern devices.
MAKING CONNECTION (showing high level of understanding)
MC1: Show the path of the alpha particle from question 15 as it enters the electric field ( no
magnetic field) Briefly explain why you drew your path this way.
Here is a diagram of the path of the alpha particle from question 15 as it enters the electric field
with negative charges at the top and positive charges at the bottom (no magnetic field):
9. 9
The alpha particle is deflected towards the negative plate because it is positively charged. The
electric field is directed from the positive plate to the negative plate, so the alpha particle
experiences a force in the direction of the negative plate. The alpha particle will continue to be
deflected until it reaches the negative plate.
MC2: Yaz runs an experiment and find outs that the electric potential energy of a particle has
a linear relationship with its charge and inversely proportional to the distance from the
particle creating the field. He suggests the following formula.
𝑼𝒆 =
𝒏𝒌𝒒
𝒓
⁄
Regardless whether the formula is correct or incorrect, justify whether is constituent with
Yaz’s findings in the lab.
Discussion
10. 10
Yaz's formula is consistent with his findings in the lab. The electric potential energy of a particle
is given by the following formula:
𝑼𝒆 =
𝒌𝒒𝟏𝒒𝟐
𝒓
⁄
where:
𝑼𝒆 is the electric potential energy
k is Coulomb's constant
𝒒𝟏 is the charge of the first particle
𝒒𝟐 is the charge of the second particle
r is the distance between the two particles
Yaz's formula is a simplified version of this formula. In Yaz's formula, n is a constant that Yaz
has determined experimentally. The value of n is likely to be different for different particles and
different electric fields.
Bonus: Explain the theory of gravitons. What are they? How do they explain the existence
of the force of gravity?
The theory of gravitons states that gravity is mediated by a particle called the graviton. Gravitons
are massless, spin-2 elementary particles that are believed to be exchanged between objects that
have mass. The exchange of gravitons between two objects is what causes the force of gravity.
The theory of gravitons is still a work in progress, but it has the potential to unify general
relativity and quantum mechanics. General relativity is a theory of gravity that describes gravity
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as a curvature of spacetime. Quantum mechanics is a theory of physics that describes the
behavior of matter and energy at the atomic and subatomic level.
The theory of gravitons could unify these two theories by describing gravity as a quantum field
theory. A quantum field theory is a theory that describes the behavior of particles and fields at the
quantum level.
If the theory of gravitons is correct, it would mean that gravity is not a fundamental force, but
rather a consequence of the exchange of gravitons between objects. This would have profound
implications for our understanding of the universe.
Here are some additional details about gravitons:
Gravitons are thought to be very weakly interacting particles. This means that they interact very
rarely with other particles.
Gravitons are also thought to be very massive. This means that they have a very high energy.
Gravitons have not yet been directly detected, but there is indirect evidence for their existence.
The theory of gravitons is a very promising theory, but it is still under development. If the theory
is correct, it would be a major breakthrough in our understanding of the universe.
