Physics II Exam 1 (Chapters 21-23)

Extra study sources

Someone's test: http://2ksfe2u6shz19ksvbbdjiwkg.wpengine.netdna-cdn.com/wp-content/uploads/2015/07/Exam-2-KEY-PHY2049.pdf Electrostatics true/false quizlet: https://quizlet.com/305126572/physics-true-false-electrostatics-flash-cards/

An electron is initially moving to the right when it enters a uniform electric field directed upwards. Which trajectory shown below will the electron follow? W (straight ahead) Z (curved down) Y (curved up) X (straight up right away)

Z (curved down) because that is where the positive side is as electric fields go + --> -

The figure shows three electric charges labeled Q1, Q2, Q3, and some electric field lines in the region surrounding the charges. What are the signs of the three charges? (Lines point away from both Q1 and Q3, towards Q2) A) Q1 pos, Q2 neg, Q3 pos B) Q1 pos, Q2 pos, Q3 neg C) Q1 neg, Q2 pos, Q3 neg D) All positive E) All neg

A) Q1 pos, Q2 neg, Q3 pos

When two point charges are a distance d apart, the electric force that each one feels from the other has magnitude F. In order to make this force twice as strong, the distance would have to be A) 2d B) d/√2 C) 2/√d D) d/4 E) d/2

B) d/√2

A negative charge, if free, will tend to move A) in the direction of the electric field. B) from low potential to high potential. C) away from infinity. D) toward infinity. E) from high potential to low potential.

B) from low potential to high potential

Suppose you have two point charges of opposite sign. As you move them farther and farther apart, the potential energy of this system relative to infinity A) decreases. B) increases. C) stays the same.

B) increases

If the electric field is zero everywhere inside a region of space, the potential must also be zero in that region. True/False?

False, potential could be at a maximum or minimum

Two point charges Q1 and Q2 of equal magnitudes and opposite signs are positioned as shown in the figure. Which of the arrows best represents the net electric field at point P due to these two charges? A B C D The field is equal to zero at point P

A (towards the point charges) because Q2 is closer and negative http://2ksfe2u6shz19ksvbbdjiwkg.wpengine.netdna-cdn.com/wp-content/uploads/2015/07/Exam-2-KEY-PHY2049.pdf

Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude F due to the other. With time, charge gradually leaks off of both spheres. When each of the spheres has lost half its initial charge, the magnitude of the electrostatic force will be A) 1/4 F B) 1/2 F C) 1/16 F D) 1/8 F

A) 1/4 F

One very small uniformly charged plastic ball is located directly above another such charge in a test tube as shown in the figure. The balls are in equilibrium a distance d apart. If the charge on each ball is doubled, the new equilibrium distance between the balls in the test tube would become A) 2d B) 2/√d C) 4d D) 8d

A) 2d

An uncharged conductor has a hollow cavity inside of it. Within this cavity there is a charge of +10µC that does not touch the conductor. There are no other charges in the vicinity. Which statement about this conductor is true? (There may be more than one correct choice.) A) The outer surface of the conductor contains +10µC of charge and the inner surface contains -10µC. B) The inner and outer surfaces of the conductor each contain charges of -5µC. C) The inner surface of the conductor carries a charge of -10µC and its outer surface carries no excess charge. D) The net electric field within the material of the conductor points away from the +10µC charge. E) Both surfaces of the conductor carry no excess charge because the conductor is uncharged.

A) The outer surface of the conductor contains +10µC of charge and the inner surface contains -10µC.

Suppose you have two negative point charges. As you move them farther and farther apart, the potential energy of this system relative to infinity A) decreases. B) increases. C) stays the same.

A) decreases

Two long straight parallel lines, #1 and #2, carry uniform positive linear charge densities. The charge density on line #2 is twice as great as the charge density on line #1. The focus of points where the electric field due to these lines is zero is A) along a line between the lines closer to line #2 than line #1. B) along a line between the lines closer to line #1 than line #2. C) at a point midway between the lines. D) along a line perpendicular to lines #1 and #2.

B) along a line between the lines closer to line #1 than line #2

Three equal negative point charges are placed at three of the corners of a square of side d as shown in the figure (square with negative charges in top and bottom left corners and bottom right corner). Which of the arrows represents the direction of the net electric field at the center of the square? A (towards top right) B (towards bottom right) C (towards bottom left) D (towards top left) The field is equal to zero at point P

C (towards bottom left charge) because the top left and bottom right charges cancel out and electric field goes towards the negative charge remaining

Which statements are true for an electron moving in the direction of an electric field? (There may be more than one correct choice.) A) Its electric potential energy decreases as it goes from high to low potential. B) Its kinetic energy increases as it moves in the direction of the electric field. C) Its kinetic energy decreases as it moves in the direction of the electric field. D) Its electric potential energy increases as it goes from high to low potential. E) Its potential energy increases as its kinetic energy decreases.

C D E

Four equal negative point charges are located at the corners of a square, their positions in the xy-plane being (1,1), (−1,1), (−1,−1), (1,−1). The electric field on the x-axis at (1,0) points in the same direction as A) i^ B) j^ C) -i^ D) -j^

C) -i^ (-x direction // to left)

A charge Q is uniformly spread over one surface of a very large nonconducting square elastic sheet having sides of length d. At a point P that is 1.25 cm outside the sheet, the magnitude of the electric field due to the sheet is E. If the sheet is now stretched so that its sides have length 2d, what is the magnitude of the electric field at P? A) E/2 B) 4E C) E/4 D) E E) 2E

C) E/4 because the area has increased from L² to (2L)² = 4L². SO the area is 4 times bigger. The surface charged density is therefore 4 times smaller.

Suppose a region of space has a uniform electric field, directed towards the right, as shown in the figure. (A is closest to the left with B directly under it, C is in the middle) Which statement about the electric potential is true? A) The potential at all three locations (A, B, C) is the same because the field is uniform. B) The potential at points A and B are equal, and the potential at point C is higher than the potential at point A. C) The potential at points A and B are equal, and the potential at point C is lower than the potential at point A. D) The potential at point A is the highest, the potential at point B is the second highest, and the potential at point C is the lowest.

C) The potential at points A and B are equal, and the potential at point C is lower than the potential at point A

A nonconducting sphere contains positive charge distributed uniformly throughout its volume. Which statements about the potential due to this sphere are true? All potentials are measured relative to infinity. (There may be more than one correct choice.) A) The potential at the center is the same as the potential at infinity. B) The potential at the surface is higher then the potential at the center. C) The potential is highest at the center of the sphere. D) The potential at the center of the sphere is zero. E) The potential at the center of the sphere is the same as the potential at the surface.

C) The potential is highest at the center of the sphere.

Under electrostatic conditions, the electric field just outside the surface of any charged conductor A) is always zero because the electric field is zero inside conductors. B) is perpendicular to the surface of the conductor only if it is a sphere, a cylinder, or a flat sheet. C) is always perpendicular to the surface of the conductor. D) can have nonzero components perpendicular to and parallel to the surface of the conductor. is always parallel to the surface.

C) is always perpendicular to the surface of the conductor.

At a distance D from a very long (essentially infinite) uniform line of charge, the electric field strength is 1000 N/C. At what distance from the line will the field strength to be 2000 N/C? A) D/√2 B) 2√D C) 2D D) D/2 E) D/4

D) D/2

A negative charge is moved from point A to point B along an equipotential surface. Which of the following statements must be true for this case? A) Work is done in moving the negative charge from point A to point B. B) Work is required to move the negative charge from point A to point B. C) The work done on the charge depends on the distance between A and B. D) No work is required to move the negative charge from point A to point B. E) The negative charge performs work in moving from point A to point B.

D) No work is required to move the negative charge from point A to point B

Consider a spherical Gaussian surface of radius R centered at the origin. A charge Q is placed inside the sphere. To maximize the magnitude of the flux of the electric field through the Gaussian surface, the charge should be located A) at x = 0, y = R/2, z = 0. B) at x = R/2, y = 0, z = 0. C) at x = 0, y = 0, z = R/2. D) at the origin. E) The charge can be located anywhere, since flux does not depend on the position of the charge as long as it is inside the sphere.

E)The charge can be located anywhere, since flux does not depend on the position of the charge as long as it is inside the sphere.

If the electric flux through a closed surface is zero, the electric field at points on that surface must be zero. True/False?

False

If the electric potential at a point in space is zero, then the electric field at that point must also be zero. True/False?

False

When the electric field is zero at a point, the potential must also be zero there. True/False?

False

If the electrical potential in a region is constant, the electric field must be zero everywhere in that region. True/False?

True

The figure shows four Gaussian surfaces surrounding a distribution of charges. (a) Which Gaussian surfaces have an electric flux of +q/ε0 through them? b c d a

b because the total charge in the surface with +2q and -q comes to be +q