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?

(I) How long does it take light to reach us from the Sun, $1.50 \times 10^{8}$ km away?

The generator of a car idling at $875 \mathrm{~rpm}$ produces $12.4 \mathrm{~V}$. What will the output be at a rotation speed of $1850 \mathrm{~rpm}$ assuming nothing else changes?

The generator of a car idling at 1100 rpm produces 12.4 V. What will the output be at a rotation speed of 2500 rpm, assuming nothing else changes?

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.

What would be the effect on $B$ inside a long solenoid if the solenoid's length was halved along with a doubling in the total number of loops?

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?