PHYSICS 121 MULTIPLE CHOICE QUESTIONS WITH
VERIFIED ANSWERS
1. Two point charges, Q1 and Q2 are separated by a distance R. If the magnitudes of
BOTH charges are Doubled and their separation is doubled, what happens to the
electrical force that each charge exerts on the other one?
A) increases by factor of 2
B) increases by factor of sqrt(2)
C) decreases by factor of sqrt(2)
D) increases by factor of 4
E) remains the same - Answers - E
F = Q1Q2/r^2
2. What is the direction of the electric field at the position of the X?
A) 1
B) 2
C) 3
D) 4
E) 5 - Answers - B
3. The figure shows two unequal charges +q and -Q has greater magnitude than charge
+q. Point X is midway between the charges. In what section of the line will there be a
point where the resultant electric field is zero?
A) VW
B) WX
C) XY
D) YZ - Answers - A
4. A thin rod with length L has a total charge of Q distributed uniformly along its length is
located on the x-axis with one end at the origin as shown. Which expression represents
the electric field due to this rod at a point on the x-axis a distance a to the left of the
origin?
What is r in dE = k dq/r^2
A) a+x
B) x-a
C) x
D) a - Answers - A
, lambda = Q/L
Dq = lambda dx = Q/L dx R=x-(-a)=x+a
De = - k Q/L (1 / (a+x)^2) dx
5. Points p and q are connected to a battery of fixed voltage. As more resistors R are
added to the parallel circuit, what happens to the total current in the circuit?
A) increases
B) remains the same
C) decreases
D) drops to zero - Answers - A
6. Consider the shown. Which of the following statements best describes the current
flowing in the wire connecting points a and b
A) positive current flows from a to b
B) positive current flows from b to a
C) no current flows between a and b
D) none of the above - Answers - B
7. In the figure, two identical charges are located at the vertices of an equilateral
triangle. The work required to bring another identical charge from infinity to the other
vertex (marked by X) is
What is the factor?
A) 0
B) 1/4
C) 2/4
D) 3/4
E) 6/4 - Answers - C
8. Find the magnitude of the electric field at the origin
Find factor in |E| = | sigma | / Eo
A) sigma p / Eo
B) sigma s / Eo
C) sigma s / 2Eo
D) sigma s + 2 sigma p / 2Eo
E) sigma s - 2 sigma p / 2Eo - Answers - C
10. Find the surface-charge density sigma k on the right-hand surface of the metal slab
(the place containing point C)
A) sigma s / 2
B) 2 sigma p
VERIFIED ANSWERS
1. Two point charges, Q1 and Q2 are separated by a distance R. If the magnitudes of
BOTH charges are Doubled and their separation is doubled, what happens to the
electrical force that each charge exerts on the other one?
A) increases by factor of 2
B) increases by factor of sqrt(2)
C) decreases by factor of sqrt(2)
D) increases by factor of 4
E) remains the same - Answers - E
F = Q1Q2/r^2
2. What is the direction of the electric field at the position of the X?
A) 1
B) 2
C) 3
D) 4
E) 5 - Answers - B
3. The figure shows two unequal charges +q and -Q has greater magnitude than charge
+q. Point X is midway between the charges. In what section of the line will there be a
point where the resultant electric field is zero?
A) VW
B) WX
C) XY
D) YZ - Answers - A
4. A thin rod with length L has a total charge of Q distributed uniformly along its length is
located on the x-axis with one end at the origin as shown. Which expression represents
the electric field due to this rod at a point on the x-axis a distance a to the left of the
origin?
What is r in dE = k dq/r^2
A) a+x
B) x-a
C) x
D) a - Answers - A
, lambda = Q/L
Dq = lambda dx = Q/L dx R=x-(-a)=x+a
De = - k Q/L (1 / (a+x)^2) dx
5. Points p and q are connected to a battery of fixed voltage. As more resistors R are
added to the parallel circuit, what happens to the total current in the circuit?
A) increases
B) remains the same
C) decreases
D) drops to zero - Answers - A
6. Consider the shown. Which of the following statements best describes the current
flowing in the wire connecting points a and b
A) positive current flows from a to b
B) positive current flows from b to a
C) no current flows between a and b
D) none of the above - Answers - B
7. In the figure, two identical charges are located at the vertices of an equilateral
triangle. The work required to bring another identical charge from infinity to the other
vertex (marked by X) is
What is the factor?
A) 0
B) 1/4
C) 2/4
D) 3/4
E) 6/4 - Answers - C
8. Find the magnitude of the electric field at the origin
Find factor in |E| = | sigma | / Eo
A) sigma p / Eo
B) sigma s / Eo
C) sigma s / 2Eo
D) sigma s + 2 sigma p / 2Eo
E) sigma s - 2 sigma p / 2Eo - Answers - C
10. Find the surface-charge density sigma k on the right-hand surface of the metal slab
(the place containing point C)
A) sigma s / 2
B) 2 sigma p
