NSAA Physics - Electricity and Magnetism Flashcards

What is the energy stored in a capacitor of capacitance 4 F charged to 3 V?

Answer: 18 J

Energy = ½CV² = ½ × 4 × 9 = 18 J.

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?

Answer: 100 V

Vs/Vp = Ns/Np → Vs = 20 × (500/100) = 100 V.

A positive charge is released from rest between two parallel plates with the positive plate on the left. In which direction will it accelerate?

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.

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:

Answer: 4F

Coulomb's Law: F ∝ 1/r²; halving distance multiplies force by 4.

An electron moves with velocity v perpendicular to a magnetic field B. What is the shape of its path?

Answer: Circle

The magnetic force always acts perpendicular to velocity, providing constant centripetal force, resulting in circular motion.

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?

Answer: 8 V

I = EMF/(r+R) = 9/9 = 1 A; Terminal voltage = EMF - Ir = 9 - 1×1 = 8 V.