NSAA NSAA Physics - Electricity and Magnetism 3 — Questions and Answers
Question 1: What is the energy stored in a capacitor of capacitance 4 F charged to 3 V?
- 6 J
- 12 J
- 18 J (Correct answer)
- 36 J
Correct answer: 18 J
Energy = ½CV² = ½ × 4 × 9 = 18 J.
Question 2: In a step-up transformer, the primary coil has 100 turns and the secondary has 500 turns. If the primary voltage is 20 V, what is the secondary voltage?
- 4 V
- 20 V
- 100 V (Correct answer)
- 200 V
Correct answer: 100 V
Vs/Vp = Ns/Np → Vs = 20 × (500/100) = 100 V.
Question 3: A positive charge is released from rest between two parallel plates with the positive plate on the left. In which direction will it accelerate?
- To the left (toward positive plate)
- To the right (toward negative plate) (Correct answer)
- Upward
- It will not move
Correct answer: To the right (toward negative plate)
Electric field points from positive to negative plate; positive charges accelerate in the field direction, toward the negative plate.
Question 4: Two point charges of +2 C and +8 C are 3 m apart. The electric force between them is F. If the distance is halved to 1.5 m, the new force is:
- F/4
- F/2
- 2F
- 4F (Correct answer)
Correct answer: 4F
Coulomb's Law: F ∝ 1/r²; halving distance multiplies force by 4.
Question 5: An electron moves with velocity v perpendicular to a magnetic field B. What is the shape of its path?
- Straight line
- Parabola
- Circle (Correct answer)
- Ellipse
Correct answer: Circle
The magnetic force always acts perpendicular to velocity, providing constant centripetal force, resulting in circular motion.
Question 6: A circuit has an EMF of 9 V and internal resistance of 1 Ω connected to an external resistor of 8 Ω. What is the terminal voltage?
- 1 V
- 8 V (Correct answer)
- 9 V
- 10 V
Correct answer: 8 V
I = EMF/(r+R) = 9/9 = 1 A; Terminal voltage = EMF - Ir = 9 - 1×1 = 8 V.
NSAA NSAA Physics - Electricity and Magnetism 3
What is the energy stored in a capacitor of capacitance 4 F charged to 3 V?