AP Physics Physics: Electricity & Magnetism 5

Question 1

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

Accepted Answer

600 V

Answer

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

Question 2

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

Accepted Answer

Q(V_A − V_B)

Answer

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

Question 3

Which statement about electric field lines is INCORRECT?

Accepted Answer

They can cross each other at points of equal potential

Answer

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

Question 4

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

Accepted Answer

ε/R

Answer

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

Question 5

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:

Accepted Answer

10 V

Answer

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

AP Practice Test