A dc generator is rated at 10 kW, 200 V, and 50 A when it rotates at $1000$ rpm. The resistance of the armature windings is $0.40 ~\Omega$. (a) Calculate the "no-load" voltage at $1000$ rpm (when there is no circuit hooked up to the generator). (b) Calculate the full-load voltage (i.e. at $50 ~\mathrm{A}$) when the generator is run at $800$ rpm. Assume that the magnitude of the magnetic field remains constant.

A dc generator is rated at $16 \mathrm{~kW}, 250 \mathrm{~V}$, and $64 \mathrm{~A}$ when it rotates at $1000 \mathrm{rpm}$. The resistance of the armature windings is $0.40 \Omega$. (a) Calculate the "no-load" voltage at $1000 \mathrm{rpm}$ (when there is no circuit hooked up to the generator).

A current $I=1.80 \cos 377 t$ ( $I$ in amps, $t$ in seconds, and the "angle" is in radians) flows in a series $L R$ circuit in which $L=3.85 \mathrm{mH}$ and $R=1.35 \mathrm{k} \Omega$. What is the average power dissipation?

Image intensifiers used in night-vision devices create a bright image from dim light by letting the light first fall on a photocathode. Electrons emitted by the photoelectric effect are accelerated and then strike a phosphorescent screen, causing it to glow more brightly than the original scene. Recent devices are sensitive to wavelengths as long as 900 nm, in the infrared. a. If the threshold wavelength is 900 nm, what is the work function of the photocathode? b. If light of wavelength 700 nm strikes such a photocathode, what will be the maximum kinetic energy, in eV, of the emitted electrons?

Your 300 mL cup of coffee is too hot to drink when served at $90^{\circ} \mathrm{C}$. What is the mass of an ice cube, taken from a $-20^{\circ} \mathrm{C}$ freezer, that will cool your coffee to a pleasant $60^{\circ} \mathrm{C}$?

The electron in a certain hydrogen atom has an angular momentum of $8.948 \times 10^{-34} \mathrm{J} \cdot \mathrm{s}$. What is the largest possible magnitude for the z component of the angular momentum of this electron? For accuracy, use $h=6.626 \times 10^{-34} \mathrm{J} \cdot \mathrm{s}$.

A Hall-effect probe operates with a 120-mA current. When the probe is placed in a uniform magnetic field of magnitude 0.080 0 T, it produces a Hall voltage of $0.700 \mu \mathrm{V}$ (a) When it is used to measure an unknown magnetic field, the Hall voltage is $0.330 \mu \mathrm{V}.$ What is the magnitude of the unknown field? (b) The thickness of the probe in the direction of $\overrightarrow{\mathbf{B}}$ is 2.00 mm. Find the density of the charge carriers, each of which has charge of magnitude e.

An LRC resonant circuit is often called an oscillator circuit. What is it that oscillates?

A radar transmitter contains an LC circuit oscillating at $1.00 \times 10^{10}\ \mathrm{Hz}.$ (a) For a one-turn loop having an inductance of 400 pH to resonate at this frequency, what capacitance is required in series with the loop? (b) The capacitor has square, parallel plates separated by 1.00 mm of air. What should the edge length of the plates be? (c) What is the common reactance of the loop and capacitor at resonance?

The following questions refer to the circuit shown in Figure 18.114, consisting of two flashlight batteries and two Nichrome wires of different lengths and different thicknesses as shown (corresponding roughly to your own thick and thin Nichrome wires). The thin wire is 50 cm long, and its diameter is 0.25 mm. The thick wire is 15 cm long, and its diameter is 0.35 mm. The emf of each flashlight battery is 1.5 V. Determine the steady-state electric field inside each Nichrome wire. Remember that in the steady state you must satisfy both the current node rule and energy conservation. These two principles give you two equations for the two unknown fields.

The magnetic field of a "shunt-wound" dc motor is produced by field coils placed in parallel to the armature coils. Suppose that the field coils have a resistance of $66.0 ~\Omega$ and the armature coils $5.00 ~\Omega$. The back emf at full speed is $105 ~\mathrm{V}$ when the motor is connected to a $115$-$\mathrm{V}$ line. (a) Draw the equivalent circuit for the situations when the motor is just starting and when it is running full speed. (b) What is the total current drawn by the motor at start up? (c) What is the total current drawn when the motor runs at full speed?

Sheena can row a boat at 3.00 mi/h in still water. She needs to cross a river that is 1.20 mi wide with a current flowing at 1.60 mi/h. Not having her calculator ready, she guesses that to go straight across, she should head

$$60.0 ^ { \circ }$$

upstream. (a) What is her speed with respect to the starting point on the bank? (b) How long does it take her to cross the river? (c) How far upstream or downstream from her starting point will she reach the opposite bank? (d) In order to go straight across, what angle upstream should she have headed?

An open container holds $0.550$ $\mathrm{kg}$ of ice at $-15.0\degree \mathrm{C}$. The mass of the container can be ignored. Heat is supplied to the container at the constant rate of $800.0 \mathrm{~J} /$min for $500.0$ min.
($c$) Plot a curve showing the temperature as a function of the elapsed time.

In the problems, please assume the free-fall acceleration g=9.80

$$m/s^2$$

unless a more precise value is given in the problem statement. Ignore air resistance. At 3:00 P.M., a bank robber is spotted driving north on I-15 at milepost 126. His speed is 112.0 mi/h. At 3:37 P.M., he is spotted at milepost 185 doing 105.0 mi/h. During this time interval, what are the bank robber's displacement, average velocity, and average acceleration? (Assume a straight highway.)