PHYS165 / PHYS 165 Module 7: (Latest Update
2026 / 2027) Physics | Questions, Answers &
Review Material | Grade A | 100% Correct -
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2026 / 2027 Academic Year
Q: True or False: Atoms are made up of protons, neutrons, and electrons. Protons carry a positive
charge, electrons carry a negative charge, and neutrons do not carry any charge.
True
Q: True or False: When something acquires a net charge, it can be either the protons or the
electrons that move, but not the neutrons.
False
Q: What is the unit of charge?
Coulombs
Q: True or False: Two identical, conductive spheres have net charges on them. Sphere A has a
net charge of +2.50 mC and sphere B has a net charge of +3.81 mC. The two spheres are released in
space and move only because of the electrostatic forces between them. When released, the two
spheres should move away from each other.
True
Q: What is the name of a device that stores electric charge?
Capacitor
Q: A variable capacitor has too much capacitance. Which of the following changes would NOT
reduce the capacitance of this capacitor?
Switch the dielectric for a new one that has a larger dielectric constant
Q: When you rub a balloon on your hair, it scrapes electrons off your hair and deposits them
onto the balloon. The balloon becomes negatively charged, and your hair becomes positively
charged. What is the name of this process of charging an object?
Fricton
Q: True or False: The Fundamental Law of Electrostatics states that opposite charges repel each
other while like charges attract each other.
False. Opposite Charges Attract/Like Charges Repel
Q: When a lightning bolt strikes a tree, -8.42 C of charge is transferred from the ground up to
the clouds. How many electrons were transferred to the clouds from the tree?
Take the charge; convert using (1e-/-1.60x10^-19C)
Answer in electrons
Q: An atom of Potassium-40 has 19 protons, 20 neutrons, and 18 electrons. What is the sign
and magnitude of the net charge of this atom in Coulombs?
19-18 = +1e- (1.60x10^-19/1e-) = 1.60x10^-19
Answer in C
Q: A purple metal nut has been given a net charge of + 6325 nC, and an orange metal nut has
been given a net charge of - 3614 nC. Answer the following questions:
a. What is the magnitude of the electrostatic force between these two nuts if they are separated by
25 cm?
b. Is the force attractive or repulsive?
c. Which nut has the largest electrostatic force acting on it?
a) F= kq1q2/r^2 where k= 9.0x10^9Nm^2/kg^2
Answer in Newtons
b) Force is negative so it's attractive
c) Both nuts feel the same force
Q: A proton is in an electric field with a magnitude of 3.79 x 106 N/C directed to the West.
a. What is the magnitude of the electric force acting on the proton?
b. In what direction is the force acting on the proton?
c. If this is the only force acting on the proton and the mass of the proton is 1.67 x 10-27 kg, what is
the acceleration of the proton?
d. If the proton is replaced with an electron, how will the magnitude and direction of the force acting
on the electron compare to the force exerted on the proton?
a) E=F/q Revised as F=EQ Answer in Newtons
B) West
C) Use F=ma Revised as a=F/m Answer in m/s^2
D) It is the same magnitude, directed East
Q: A 26.0-nF capacitor is connected to a 36.0-v battery. The plate separation is 35.4 µm and
there is a vacuum in between the plates.
Eo=8.85x10^-12C^2/Nm^2
a. What is the area of one of the plates?
b. How much charge is stored on one of the plates?
c. How much energy is stored in the capacitor?
a) C=EoA/d revised as A=dC/Eo Answer in m^2
b) Q=CV (2.60x10^-8F)(12.0V) Answer in MewC (?)
c) Uc=C(deltaV)^2/2
Answer in Mew J
Q: Three charged spheres are positioned on a number line. The red sphere is located at the
origin and has a net charge of +4.36 nC. The green sphere is located at the 25.0 cm mark and has a
net charge of -6.94 nC. The blue sphere is located at the 75.0 cm mark and has a net charge of +9.32
nC.
A. What is the magnitude of the force of the red sphere acting on the green sphere?
B. What is the magnitude of the force of the blue sphere acting on the green sphere?
C. Do the red and blue spheres repel or attract the green sphere?
D. What is the magnitude of the net force acting on the green sphere?
E. What is the direction of the net force acting on the green sphere? (towards the red or blue
sphere?)
A) F(RonG)= k*QrQg/r^2
where k=9x10^9Nm^2/C^2
Answer in Newtons
B) F(BonG) k*QrQg/r^2 where k=9x10^9Nm^2/C^2
Answer in Newtons
C) The blue and red spheres both repel the green sphere in the middle
D) To find the net force we need to subtract the magnitudes
F(RonG) - F(BonG)
E) Since the force from the red sphere is bigger than the one from the blue sphere, the net force will
be away from the red sphere, which is also towards the blue sphere.
Q: A 56.0 nF capacitor is connected to a 7.50 v battery. The plate separation is 25.4 µm and
there is a vacuum in between the plates.
Eo = 8.85x10^-12 C^2/Nm^2
a. What is the area of one of the plates?
b. How much charge is stored on one of the plates?
c. How much energy is stored in the capacitor?
a) C=Eo*A/d Revised as A=dC/Eo Answer in m^2
b) Q=CV Answer in mewC
c) Uc= C*deltaV^2/2 Answer in mewJ
Q: A negatively charged rod touches a neutral electroscope, giving the electroscope a net charge.
a. What is the name of this process of charging an object?
b. What is the sign of the net charge of the electroscope after the rod touches it?
a) Charging by conduction
b) Negative
Q: Three charged spheres are positioned on a number line. The red sphere is located at the
origin and has a net charge of +5.36 nC. The green sphere is located at the 25.0 cm mark and has a
net charge of -7.94 nC. The blue sphere is located at the 75.0 cm mark and has a net charge of +8.32
nC. What is the magnitude and direction of the net force acting on the green sphere?
a) F(RonG)= kQrQg/r^2 Answer in Newtons
F(BonG)kQrQg/r^2
Answer in Newtons
The blue and red spheres both repel the green sphere in the middle. To find the net force we will
need to subtract the two magnitudes
F(RonG) -F(BonG) Answer in Newtons
Since the force from the red sphere is bigger than the one from the blue sphere, the net force will be
away from the red sphere which is also towards the blue sphere
Q: Two charged spheres are separated by 47.0 cm. The yellow sphere has a net change of -8.69
nC, and the purple sphere has a net charge of +4.32 nC.
a. What is the magnitude of the net electric field halfway between these two charges?
b. What is the direction of the net electric field halfway between these two charges?
c. What is the total voltage halfway between these two charges?
a) Eyellow = kqy/r^2 Answer in N/C
Epurple=kqp/r^2
Answer in N/C
Both fields are towards the yellow charge so to get the net electric field we need to add the
magnitude
Eyellow= Eyellow+ Epurple Answer in N/C
b) The direction of the net electric field is towards the yellow charge
c) Vyellow = kqy/r answer in Volts
Vpurple=kqp/r
answer in volts
Since voltage is a scalar to get the total voltage, we simply add the magnitudes
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