Physics 121 Multiple Choice Questions and answers 100% correct 2025

Physics 121 Multiple Choice Questions
and answers 100% correct 2025
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 - correct answer ✔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 - correct answer ✔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 - correct answer ✔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 - correct answer ✔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