test 1: electrostatics & potential mcq

what equation do you use here? what is the answer?

“two point charges of +4.0μ and -2.0μC are separated by 0.30m.
the magnitude of the electric force between them is closest to…”

A) 0.40N

B) 0.80N

C) 1.6N

D) 0.80N

E) 2.4N

coulomb’s law → 0.80N
B) 0.80N

what equation is being used here? what is the answer?

“a (+) test charge is placed in a uniform electric field directed toward the east. the electric force on the charge is…”

A) west

B) east

C) north

D) south

E) zero

electric force,

B) east

which way does a (+) charge move when it is placed in an electric field?

which way does a (-) charge move when it is placed in an electric field?

it moves in the direction of the field

it moves in the opposite direction of the field

when a (+) charge is placed in an electric field, it moves from a ___ potential to a ___ potential
when a (-) charge is placed in an electric field, it moves from a ____ potential to a ____ potential

(+): high → low potential

(-): low → high potential

when a (+) charge is placed in an electric field, what happens to its electrical potential energy?

when a (-) charge is placed in an electric field, what happens to its electrical potential energy?

(+): electrical potential energy decreases

(-): electrical potential energy increases

when a (+) charge or a (-) charge is placed in an electric field, what happens to its kinetic energy?

(+): kinetic energy increases

(-): kinetic energy increases

what equation is being used here? what is the answer?

"a proton is released from rest in a uniform electric field. which statement is correct?”

A) it moves opposite the electric field

B) it remains at rest

C) its kinetic energy decreases

D) it accelerates in the direction of the electric field

E) its electric potential energy increases

electric force,

D) it accelerates in the direction of the field

how are electric field and electrostatic force and electric potential related?

electric field of a charge, E=k|Q|/r², says that the distance r² is inversely proportional to the electric field and magnitude charge |Q|

→ scale of 1/r²

electric potential, V=k(q/r), says that the distance r is inversely proportional to the algebraic charge ±q

→ scale of 1/r

scalar quantity

has only size/magnitude/intensity of a number

→ “walk 5+100 miles”

vector quantity

has size & specific direction

→ “walk 5 miles north”

what equation is being used here? what is the answer?

“at a point midway between two identical (+) charges…”

A) the electric field is zero

B) the electric potential is zero

C) both field and potential are zero

D) both field and potential are negative

E) the electric field is maximum

electric potential & electric field,

V is only scalar but E is vector

→ at the midpoint, E vectors from two identical (+) charges point in opposite directions, so they cancel out to 0

→ V adds together V_net=V₁+V₂, so potential is NOT zero

A) the electric field is zero

what equation is being used here? what is the answer?

“the electric field at a distance r from a point charge is E. at a distance 2r the field becomes…”

A) E

B) E/2

C) E/4

D) 2E

E) 4E

electric field of a charge,

E=k|Q|/r², says that the distance r² is inversely proportional (1/r²) to the electric field

→ if r is doubled it becomes ¼, making the field E ¼ of r

C) E/4

“which material allows electric charges to move most freely?”

A) glass

B) rubber

C) copper

D) plastic

E) wood

conductors (like metal) have free e^- that allow charge to move easily

C) copper

what equation is being used here? what is the answer?

“a (-) charged particle moves opposite the direction of a uniform field. it’s electric potential energy…”

A) increases

B) decreases

C) remains constant

D) becomes zero

E) cannot be determined

electric potential energy,

a (-) charge loses electrical potential energy when it moves in the opposite direction of the electric field

B) decreases

what equation is being used here? what is the answer?

“a proton moves through a potential difference of 200V. its gain in kinetic energy is…”

A) 100 eV

B) 200 eV

C) 400eV

D) 200 J

E) 400 J

change/gain in kinetic energy,

B) 200 eV

what equation is being used here? what is the answer?

“the electric potential due to a point charge is proportional to…”

A) r

B) r²

C) 1/r

D) 1/r²

E) √r

electric potential,

C) 1/r