Physics 104 Exam 1 Concept Questions

Negatively charged objects have a higher (more negative) electrical potential than negatively charged objects T/F

F (Positively charged objects have a higher (more positive) electrical potential than negatively charged objects)

Equipotential surfaces are continuous sets of points in space that are all different electric potentials T/F

F (all the same electric potential)

The charge density and electric field are greatest on a conductor where the curvature is smallest T/F

F (largest)

Current direction is defined to be the direction that negative charges flow T/F

F (positive)

When batteries of equal voltage are connected in parallel, the total voltage changes T/F

F (total voltage does not change)

Opposite charges (+-, -+): Force vector points away from q T/F

F (toward)

It takes NO WORK to move a charged particle on an equipotential surface T/F

T

Like charges (++, --) points away from q T/F

T

The electric field is always perpendicular to the surface of a conductor T/F

T

The relationship between potential difference, electric current, and resistance is given by Ohm's Law T/F

T

Excess charges on a conductor will repel each other, and will wind up being as far apart as possible. T/F

T (Any excess charge on an isolated conductor resides entirely on the surface of the conductor.)

When batteries are connected in series ,the total voltage is the sum of the individual voltages T/F

T (Think about individual cell voltages as pumps, Every time you go through another pump, the electric potential increases)

The forces between charged particle are vectors T/F

T (magnitude and direction)

Conductors 3 and 4 are made of the same material. Compare the resistances R3and R4 R3=r, L, R4=2r, 2L A) R3 > R4 B) R3 < R4 C) R3 = R4

a

The strength of the electric force exerted by one charged particle on another is proportional to the product of the charges and inversely proportional to the square of the distance between them is... a) Magnitude b) Principle of superposition c) Direction d) Coulomb's law

a

Two space heaters in your living room are operated at 120 V. Heater 2 has twice the resistance of heater 1. Which one will give off more heat? A) Heater 1 B) Heater 2 C) Both equally

a (For the same V, Power is inversely related to resistance. The one with more resistance will give off less heat.)

Two balls with charges +Q and -4Qare fixed at a distance r. Where should you place another charged ball +Q0 on the line through the two charges such that the net force on +Q0 will be zero? A) to the left of +Q B) to the right of -4Q C) Between the two charges D) It is not possible to have a net force of zero in this case

a (If you have a +Q charge, the charge needs to be placed to the left, twice as far away from the -4Q charge to balance out the forces.)

A negatively charged particle moves from point 1 to point 2. As it does, its electric potential energy (Point 1 is two positive charges, point 2 is two negative charges) A) Increases B) Decreases C) Stays the same

a (It takes work to move the neg. charge closer to the other negative charges, against an electric field. Just as with gravity, this work increases the potential energy of the charge.)

An electron is placed at the position marked by the dot. The force on the electron is... (energy all going to the right) A. to the left. B. to the right. C. zero. D. There's not enough information to tell.

a. (E=F/q, so F=qE. Since q is negative, F is in the opposite direction of E.)

Positive field lines point ______ the charge, and negative field lines point______ the charge A) towards, away from B) away from, towards C) towards, towards D) away from, away from

b

The total force on a charged particle cause by the presence of multiple other charges is the vector sum of the individual forces. a) Magnitude b) Principle of superposition c) Direction d) Coulomb's law

b

What are the signs of the charges whose electric fields are shown below? (red has electric fields pointing towards charge, green has electric fields going away from charge) A) red=+, green=- B) red=-, green=+ C) both negative D) both positive E) No way to tell

b

Which of the charges has greater magnitude? (red has 6 electric field lines, green has 12) A) red B) green C) Same

b

Capacitor C1 is connected across a battery of 5 V. An identical capacitor C2 is connected across a battery of 10 V. Which one has more charge? A) C1 B) C2 C) both have the same charge D) it depends on other factors

b (C = Q / V, and Q = CV, so charge is directly related to potential difference across the battery. The one with higher V will have more charge.)

Current runs through a tungsten light bulb filament at 20o C. As current runs through the filament it heats up, eventually reaching 1500o C What happens to the current as the temperature increases? A) Current increases B) Current decreases C) Current stays the same

b (Resistance increases with temperature so current decreases)

Two light bulbs have the same current passing through them. Light bulb 2 has twice the resistance of Light bulb 1 Which one will give off more light? A) Light 1 B) Light 2 C) Both equally

b (The bulbs in series have the same current going through them, not the same potential difference. The second one will have a higher power)

Charges 1 and 2 exert repulsive forces on each other, with F12 = 3 N. If we increase one charge to 4Q, how do the magnitudes of the forces compare? A. F12>F21 B. F12<F21 C. F12=F21

c

Which set of equipotential surfaces matches this electric field? (Long energy arrows pointing to the left, medium arrows to the left, short arrows to the left) a) equal spacing throughout (0V --> 50V) b) spacing decreases as you approach the right (0V --> 50V) c) spacing increases as you approach the right 0V --> 50V d) even spacing throughout (50V-->0V) e) spacing decreases as you approach the right (50V-->V)

c

The electric field is _____ inside a charged conductor A) positive B) negative C) zero

c (Electric charges are free to move within a conductor; therefore, there cannot be a static field within the conductor)

Rank in order, from largest to smallest, the electric potentials V1, V2, V3 (Charge 1 and 2 at same distance from q, 3 is farther away) A. V1 > V2 = V3 B. V1 = V2 > V3 C. V3 > V1 = V2 D. V3 > V2 > V1

c (Electric potential is larger when you are farther away from negative charges)

Equipotential surfaces are _______ to the electric field lines, and are ________ where the electric field is largest a) parallel, more dense b) perpendicular, less dense c) parallel, less dense d) perpendicular, more dense

d

If the current through an Ohmic resistor is halved, the power dissipated in the resistor: A)Increases by a factor of 2 B)Increases by a factor of 4 C)Decreases by half D)Decreases by a factor of 4

d

The force on one charged particle due to the presence of another is given by... a) Magnitude b) Principle of superposition c) Direction d) Coulomb's law

d

Two charged balls are repelling each other as they hang from the ceiling. What can you say about their charges? a) one is positive, the other is negative b) both are positive c) both are negative d) Could be either b) or c)

d

Two charged balls are repelling each other as they hang from the ceiling. What can you say about their charges? a) one is positive, the other is negative b) both are positive c) both are negative d) both are positive or both are negative

d

What is the direction of the electric field at the position of the X ? (cube with upper left corner=-q, upper right corner=+q, bottom left corner +q, and X placed in bottom right) a (down and to the left) b (up and to the left) c (Up and to the right) d (down and to the right) e(zero)

d (The two +Q charges give a resultant E field that is down and to the right. The -Q charge has an E field up and to the left, but smaller in magnitude (due to the larger distance))

A metal ball hangs from the ceiling by an insulating thread. The ball is attracted to a positive-charged rod held near the ball. The charge of the ball must be: a) positive b) negative c) neutral d) positive or neutral e) negative or neutral

e

A metal ball hangs from the ceiling by an insulating thread. The ball is attracted to a positive-charged rod held near the ball. The charge of the ball must be: a) positive b) negative c) neutral d) positive or neutral e) negative or neutral

e (even if the ball is neutral, the charges in the ball can be separated by induction (polarization), leading to a net attraction)