Physics Self-Test - Page 4
29- Two charges of equal magnitude are separated by some distance. If the charges are increased by 10% to get the same force between them their separation must be
- (a) increase 20%
- (b) decrease 10%
- (c) increase 10%
- (d) decrease 20%
Explanation: Force is proportional to (q·q)/r². If both charges increase to 1.1q, the numerator becomes 1.21q². To keep force identical, r² must also increase by a factor of 1.21, meaning r must increase by √1.21 = 1.1 (a 10% increase).
29- Two charges of +4μC and -16μC are separated from each other by a distance of 0.6m. At what distance should a third charge of +6μC be placed from +4μC so that the net force exerts on it will be equal zero.
- (a) 0.4 m
- (b) 0.6 m
- (c) 1.2 m
- (d) 0.3 m
30- The electric field strength of a charge is
- (a) increase with distance
- (b) decrease with distance
- (c) decrease with square of distance
- (d) decrease with cubic of distance
Explanation: E = k·Q / r², following the inverse-square law.
31- The electric potential of a charge is
- (a) increase with distance
- (b) decrease with distance
- (c) decrease with square of distance
- (d) decrease with cubic of distance
Explanation: V = k·Q / r, which is inversely proportional to distance.
32- Coulomb’s Law is valid for _______
- a) Only point charge
- b) For both point charge and distributed charge
- c) Only distributed charges
- d) Neither distributed nor point charge
33- Which one of the following is similar between electrostatic force and gravitational force?
- a) Force can be attractive or repulsive
- b) The force depends on the medium between the bodies
- c) Both the forces are strong forces
- d) Force is inversely proportional to the distance between the bodies
34- Let B be the midpoint of AC. Two point charges Q are placed at A and C. What should be the value of charge placed at B so that the system remains at equilibrium
- a) -Q/2
- b) -Q/4
- c) +Q/2
- d) +Q/4
Explanation / طريقة الحل:
[1/4πε₀ · Q²/d² + 1/4πε₀ · Q·q/(d/2)² = 0]
35- Two charges q₁, q₂ exert some amount of force on each other. What will happen to the force on q₁ if another charge q₃ is brought close to them?
- a) The force will increase
- b) The force will decrease
- c) The force remains the same
- d) The force may increase or decrease depending on whether q₃ is positive or negative
Note: While the individual interaction force strictly between q₁ and q₂ remains unchanged, the net total force experienced by q₁ depends directly on the sign and location of q₃.
36- The electric field lines diverge from _________
- a) Positive charge
- b) Negative charge
- c) Dipole
- d) Zero potential point