A transformer has $680$ turns in the primary coil and $85$ 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 120 -volt ac source powers the circuit shown. How many volts are impressed across the lightbulb, and how many amps flow through it?

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 transformer has an input of 9 volts and an output of 36 volts. If the input is changed to 12 volts, what will the output be?

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 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?

A $280$-loop circular armature coil with a diameter of $10.0 \mathrm{~cm}$ rotates at $120 \mathrm{rev} / \mathrm{s}$ in a uniform magnetic field of strength $0.45 \mathrm{~T}$. What would you do to the rotation frequency in order to double the rms voltage output?

A $280$-loop circular armature coil with a diameter of $10.0 \mathrm{~cm}$ rotates at $120 \mathrm{rev} / \mathrm{s}$ in a uniform magnetic field of strength $0.45 \mathrm{~T}$. What is the rms voltage output of the generator?

Which of the following can a transformer accomplish? $(a)$ Changing voltage but not current. $(b)$ Changing current but not voltage. $(c)$ Changing power. $(d)$ Changing both current and voltage.

The most stable nucleus in terms of binding energy per nucleon is $^ { 56 } \mathrm { Fe }.$ If the atomic mass of $^ { 56 } \mathrm { Fe }$ is 55.9349 $\mathrm { u },$ calculate the binding energy per nucleon for $^ { 56 } \mathrm { Fe }.$

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?

What factors qualify a compound as a salt? Specify which of the following compounds are salts:

$$\mathrm{CH_4},\;\mathrm{NaF},\;\mathrm{NaOH},\;\mathrm{CaO},\;\mathrm{BaSO_4},\;\mathrm{HNO_3},\;\mathrm{NH_3},\;\mathrm{KBr}.$$

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.