A model-train transformer plugs into 120-V ac and draws 0.35 A while supplying 7.5 A to the train. Is the transformer step-up or step-down?

A transformer has 320 turns in the primary coil and 120 in the secondary coil. What kind of transformer is this, and by what factor does it change the voltage? By what factor does it change the current?

A transformer is designed to change 120 V into 10,000 V, and there are 164 turns in the primary coil. How many turns are in the secondary coil?

Suppose you are holding a circular ring of wire and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced in the wire? Is a current induced when the magnet is held steady within the ring? Is a current induced when you withdraw the magnet? In each case, if your answer is yes, specify the direction.

The back emf in a motor is 95 V when the motor is operating at 1000 rpm. How would you change the motor's magnetic field if you wanted to reduce the back emf to 65 V when the motor was running at 2500 rpm?

The back emf in a motor is 72 V when operating at 1800 rpm. What would be the back emf at 2500 rpm if the magnetic field is unchanged?

A motor has an armature resistance of $3.25 \Omega .$ If it draws 8.20 A when running at full speed and connected to a 120-V line, how large is the back emf?

A generator rotates at 85 Hz in a magnetic field of 0.030 T. It has 1000 turns and produces an rms voltage of 150 V and an rms current of 70.0 A. What is the area of each turn of the coil?

A generator rotates at 85 Hz in a magnetic field of 0.030 T. It has 1000 turns and produces an rms voltage of 150 V and an rms current of 70.0 A. What is the peak current produced?

A 450-loop circular armature coil with a diameter of 8.0 cm rotates at 120 rev/s in a uniform magnetic field of strength 0.55 T. What would you do to the rotation frequency in order to double the rms voltage output?

A 450-loop circular armature coil with a diameter of 8.0 cm rotates at 120 rev/s in a uniform magnetic field of strength 0.55 T. What is the rms voltage output of the generator?

Describe how to make the impedance in an LRC circuit a minimum.

Describe briefly how the frequency of the source emf affects the impedance of an LRC circuit far from resonance (R small).

Describe briefly how the frequency of the source emf affects the impedance of an LRC circuit near resonance (R small).