A model-train transformer plugs into $120~\mathrm{V}$ ac and draws $0.35 \mathrm{~A}$ while supplying $6.5 \mathrm{~A}$ to the train. Is the transformer step-up or step-down?

A transformer has 330 primary turns and $1120$ secondary turns. The input voltage is $120 \mathrm{~V}$ and the output current is $15.0 \mathrm{~A}$. What are the output voltage and input current?

A transformer is designed to change $117 \mathrm{~V}$ into $13,500 \mathrm{~V}$, and there are $172$ turns in the primary coil. How many turns are in the secondary coil?

A dc generator is rated at $16 \mathrm{~kW}, 250 \mathrm{~V}$, and $56 \mathrm{~A}$ when it rotates at $1200 \mathrm{rpm}$. The resistance of the armature windings is $0.40~ \Omega$. Calculate the full-load voltage (i.e., at $56 \mathrm{~A}$ ) when the generator is run at $750 \mathrm{rpm}$. Assume that the magnitude of the magnetic field remains constant.

A dc generator is rated at $16 \mathrm{~kW}, 250 \mathrm{~V}$, and $56 \mathrm{~A}$ when it rotates at $1200 \mathrm{rpm}$. The resistance of the armature windings is $0.40~ \Omega$. Calculate the "no-load" voltage at $1200 \mathrm{~rpm}$ (when there is no circuit hooked up to the generator).

The back emf in a dc motor is $85 \mathrm{~V}$ when the motor is operating at $1400 \mathrm{~rpm}$. How would you change the motor's magnetic field if you wanted to reduce the back emf to $75 \mathrm{~V}$ when the motor was running at $2300 \mathrm{rpm}$ ?

What will be the current in the motor of the given example if the load causes it to run at half speed?

A dc motor has an armature resistance of $2.65 \Omega$. If it draws $7.20 \mathrm{~A}$ when running at full speed and connected to a $120~\mathrm{V}$ line, how large is the back emf?

Suppose you are holding a circular ring of wire in front of you and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced when you withdraw the magnet? For each yes answer, specify the direction. Explain your answer.

Suppose you are holding a circular ring of wire in front of you and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced when the magnet is held steady within the ring? Explain your answer.

Suppose you are holding a circular ring of wire in front of you and suddenly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced in the wire? Explain your answer.

The back emf in a dc motor is $72 \mathrm{~V}$ when operating at $1400 \mathrm{rpm}$. What would be the back emf at $2500 \mathrm{rpm}$ if the magnetic field is unchanged?

A simple generator has a square armature $6.0 \mathrm{~cm}$ on a side. The armature has $85$ turns of $0.65 \mathrm{~cm}$ diameter copper wire and rotates in a $0.65 \mathrm{~T}$ magnetic field. The generator is used to power a lightbulb rated at $12.0 \mathrm{~V}$ and $25.0 \mathrm{~W}$. At what rate should the generator rotate to provide $12.0 \mathrm{~V}$ to the bulb? Consider the resistance of the wire on the armature.

Calculate the peak output voltage of a simple generator whose square armature windings are $5.50 \mathrm{~cm}$ on a side; the armature contains $125$ loops and rotates in a field of $0.200 \mathrm{~T}$ at a rate of $120 \mathrm{rev} / \mathrm{s}$.