Physics 2212

B

B

John Travoltage -- When Jonnie rubs his foot on the carpet in his new apartment, he picks up some charges.  If he just rubs his foot on the carpet a few times and keeps his hand away from the doorknob, how will these charges behave?

	The charges will mostly stay clustered near his foot.
	The charges will spread out somewhat uniformly throughout his body (uniform density).
	The charges will move between his finger and the doorknob, creating a spark and giving Jonnie a shock.
	The charges will spread out somewhat uniformly over the surface of his body
	The charges will mostly cluster at the tip of his outstretched index finger.

The charges will spread out somewhat uniformly over the surface of his body.

When somebody's hair stand up after sliding on a playground, this is because

Question options:

	hair experiences triboelectricity
	the human is a charged conductor and hair is movable
	hair is not conducting electricity
	the human is an insulator and hair is in electric breakdown

the human is a charged conductor and hair is movable

Consider a plastic rod that is being charged up by rubbing a wool cloth. It is then brought to an initially neutral metallic sphere, and allowed to touch the sphere for a few seconds. The rod is then separated from the sphere by a small distance. After becoming separated, the rod

Question options:

	is repelled by the sphere
	is attracted to the sphere
	experiences no force due to the sphere

is repelled by the sphere

After brushing your hair, you can use your comb to pick up pieces of paper, because

Question options:

	the hair is a charged conductor and is movable and the pieces of paper too
	the charged comb charges the pieces of paper through electric breakdown of air
	the comb is charged by triboelectric effect and the paper is polarized and is attracted to the charged comb
	both the paper and the comb are charged oppositely

the comb is charged by triboelectric effect and the paper is polarized and is attracted to the charged comb

An electroscope is positively charged by touching it with a positive glass rod. The electroscope leaves spread apart and the glass rod is removed. Then a negatively charged plastic rod is brought close to the top of the electroscope, but it doesn’t touch. What happens to the leaves?

Question options:

	The leaves spread further apart.
	The leaves don't move
	One leaf moves higher, the other lower
	The leaves get closer together.

The leaves get closer together.

B

What can be used to sense the electric field created by aluminum electrodes placed in water?

Question options:

	electroscope
	fur
	LED (light-emitting diode)
	plastic rod

✅ LED (light-emitting diode)

A

Answer Choices: Surface A, Surface B, Not enough information to tell, They have the same electric field

They have the same electric field

0, 200 N m/C, 400N m²/C, Some other Value

	400 N m^2/C

0

	Surface A
	Surface B
	Surface C
	Surfaces B and C
	All three surfaces

Surface A

	Surface B has more flux
=	Surface A has more flux
	It's impossible to say without knowing more about the electric field
	The fluxes are equal

Surface A has more flux

	Flux isn't defined for an open surface.
	400 N m^2/C
	200 N m/C
	0

400 N m²/C

A conductor carries a net charge of +Q.  A cavity within the conductor contains a point charge of −Q.  What is the charge on the outer surface of the conductor in electrostatic equilibrium?

Question options:

	–Q
	+Q
	+2Q
	0

0

Consider a charge q placed on the x axis at x = 2 R and a sphere with radius R centered at the origin. What is the flux through the sphere?

Question options:

	0
	-2q/epsilon_0
	2q/epsilon_0
	-q/epsilon_0

0

D

Question options:

	0 V
	Undefined
	6 V
	3 V
	Not enough information to tell

3V

Question options:

	1/3
	Undefined without knowing the charge
	9
	3
	1/9

1/3

The electric potential inside a parallel-plate capacitor

Question options:

	decreases inversely with the square of the distance from the negative plate
	decreases inversely with distance from the negative plate
	increases linearly from the negative to the positive plate
	is constant
	decreases linearly from the negative to the positive plate

increases linearly from the negative to the positive plate

As they do,

Question options:

	A positive potential energy becomes a negative potential energy
	A positive potential energy becomes less positive
	A negative potential energy becomes less negative
	A negative potential energy becomes more negative
	A positive potential energy becomes more positive

✅ A negative potential energy becomes more negative.

	A
	B
	C
	D
	E

C

The turning point for two point charges occurs when

Question options:

	E_total = m v^2/2 + k (q1 q2)/r
	E_total = m v^2/2 + k (q1 q2)/r^2
	E_total = k (q1 q2)/r^2
	E_total = k (q1 q2)/r

Etotal​=k(q1​q2​)/r

	vf > vi
	vf = vi
	vf < vi
	Not enough information to compare the speeds at these points

vf > vi

Afterward, the proton 

Question options:

	remains at rest at B
	moves toward A with an increasing speed
	moves toward C with a steady speed
	moves toward A with a steady speed
	moves toward C with an increasing speed

moves toward A with an increasing speed

	Vd = Ve > Vc > Va = Vb
	Vb = Vc = Ve > Va = Vd
	Va = Vb = Vc = Vd = Ve
	Va = Vb > Vc > Vd = Ve
	Va = Vb = Vd = Ve > Vc

Va = Vb > Vc > Vd = Ve

If the electric field at a certain point is zero, then the electric potential at that point

Question options:

	must be zero
	We cannot tell what the potential is from the given information
	must be positive
	must be negative

✅ We cannot tell what the potential is from the given information.

Which of these two could represent the field of a point charge?

Question options:

	(a)
	(b)
	neither (a) nor (b)

A

	Charge A
	Charge B
	They have the same potential energy
	Both have zero potential energy

Charge B

	Same charge
	Both A and B
	Same potential
	Both A and C
	Same electric field

Same potential

As an electron moves from higher potential to lower potential, its electrical potential energy

Question options:

	increases
	decreases
	stays the same

increases