Physics: Electricity & Magnetism Flashcards

A transformer has 100 primary turns and 500 secondary turns. If the primary voltage is 120 V, what is the secondary voltage?

Answer: 600 V

Using the transformer equation V_s/V_p = N_s/N_p: V_s = 120 × (500/100) = 600 V.

The work done by the electric force to move a positive charge Q from point A to point B equals:

Answer: Q(V_A − V_B)

Work done by the electric force is W = Q(V_A − V_B); the charge loses potential energy moving from high to low potential.

Which statement about electric field lines is INCORRECT?

Answer: They can cross each other at points of equal potential

Electric field lines never cross because the field has a unique direction at every point; crossing would imply two directions simultaneously.

In an RL circuit connected to a DC source, after a long time the current reaches:

Answer: ε/R

After many time constants, the inductor acts as a wire (zero resistance), so the steady-state current is simply I = ε/R.

A uniform electric field of 500 V/m exists between two parallel plates separated by 0.02 m. The potential difference between the plates is:

Answer: 10 V

For a uniform field, V = Ed = 500 × 0.02 = 10 V.

Kirchhoff's Voltage Law (KVL) is a consequence of:

Answer: Conservation of energy

KVL states that the sum of voltage drops around any closed loop is zero, which follows from the conservation of energy for the electric potential.

A conducting sphere of radius R has total charge Q. The electric potential at its surface is:

Answer: kQ/R

The potential at the surface of a conducting sphere is V = kQ/R, the same as if all charge were at the center.