The current in the electron beam of a typical video display terminal is $200 \mu \mathrm{A}$. How many electrons strike the screen each minute?

Two conductors are made of the same material and have the same length. Conductor $A$ is a solid wire of diameter $D$. Conductor $B$ is a hollow tube of outside diameter $2 D$ and inside diameter $D$. Find the resistance ratio, $R_A / R_D$, measured between their ends.

A current of $4.82 \mathrm{~A}$ exists in a $12.4 \mathrm{\Omega}$ resistor for $4.60 \mathrm{~min}$. (a) How much charge and (b) how many electrons pass through any cross section of the resistor in this time?

A cow and a man are standing in a meadow when lightning strikes the ground nearby. Why is the cow more likely to be killed than the man? The responsible phenomenon is called "step voltage."

In a mass spectrometer used for commercial purposes, uranium ions of mass $238 \mathrm{u}$ and charge $+2 e$ are separated from related species. The ions are first accelerated through a potential difference of $105 \mathrm{kV}$ and then pass into a magnetic field, where they travel a $180^{\circ}$ arc of radius $97.3 \mathrm{~cm}$. They are then collected in a cup after passing through a slit of width $1.20 \mathrm{~mm}$ and a height of $1.14 \mathrm{~cm}$. (a) What is the magnitude of the (perpendicular) magnetic field in the separator? If the machine is designed to separate out $90.0 \mathrm{mg}$ of material per hour, calculate $(b)$ the current of the desired ions in the machine and $(c)$ the internal energy dissipated in the cup in $1.00 \mathrm{~h}$.

The given Figure shows an arrangement used to measure the masses of ions. An ion of mass $m$ and charge $+q$ is produced essentially at rest in source S, a chamber in which a gas dis. charge is taking place. The ion is accelerated by potential dif. ference $\Delta V$ and allowed to enter a magnetic field $\overrightarrow{\mathrm{B}}$. In the field it moves in a semicircle, striking a photographic plate at distance $x$ from the entry slit. Show that the ion mass $m$ is given by

$$m=\frac{B^2 q}{8 \Delta V} x^2$$

Bainbridge's mass spectrometer, separates ions having the same velocity. The ions, after entering through slits $S_1$ and $S_2$, pass through a velocity selector composed of an electric field produced by the charged plates P and $\mathbf{P}^{\prime}$, and a magnetic field $\overrightarrow{\mathbf{B}}$ perpendicular to the electric field and the ion path. Those ions that pass undeviated through the crossed $\overrightarrow{\mathbf{E}}$ and $\overrightarrow{\mathbf{B}}$ fields enter into a region where a second magnetic field $\vec{B}^{\prime}$ exists, and are bent into circular paths. A photographic plate registers their arrival. Show thal $q / m=E / r B B^{\prime}$, where $r$ is the radius of the circular orbit.

The electrons in the beam of a television tube have a kinetic energy of $12.0 \mathrm{keV}$. The tube is oriented so that the electrons move horizontally from magnetic south to magnetic north. The vertical component of the Earth's magnetic field points down and has a magnitude of $55.0 \mu \mathrm{T}$. (a) In what direction will the beam deflect? (b) What is the acceleration of a given electron due to the magnetic field? (c) How far will the beam deflect in moving $20.0 \mathrm{~cm}$ through the television tube?

An electron has an initial velocity $(12.0 \mathrm{~km} / \mathrm{s}) \hat{\mathbf{j}}+(15.0 \mathrm{~km} / \mathrm{s}) \hat{\mathbf{k}}$ and a constant acceleration of $\left(2.00 \times 10^{12} \mathrm{~m} / \mathrm{s}^2\right) \hat{\mathbf{i}}$ in a region in which uniform electric and magnetic fields are present. If $\overrightarrow{\mathrm{B}}=(400 \mu \mathrm{T}) \hat{\mathbf{i}}$. find the electric field $\vec{E}$.

An electron that is moving through a uniform magnetic field has velocity $\vec{v}=(40 \mathrm{~km} / \mathrm{s}) \hat{i}+(35 \mathrm{~km} / \mathrm{s}) \hat{\mathrm{j}}$ when it experiences a force $\vec{F}=-(4.2 \mathrm{f~N}) \hat{\mathrm{i}}+(4.8 \mathrm{f~N}) \hat{\mathrm{j}}$ due to the magnetic field. If $B_x=0$, calculate the magnetic field $\vec{B}$.

A coil is formed by winding 250 turns of insulated gauge 8 copper wire in a single layer on a cylindrical form whose radius is $12.2 \mathrm{~cm}$. Find the resistance of the coil. Neglect the thickness of the insulation.

When the lights of an automobile are switched on, an ammeter in series with them reads $10.0 \mathrm{~A}$ and a voltmeter connected across them reads $12.0 \mathrm{~V}$ as shown in given figure. When the electric starting motor is turned on, the ammeter reading drops to $8.00 \mathrm{~A}$ and the lights dim somewhat. If the intemal resistance of the battery is $50.0 \mathrm{~m} \Omega$ and that of the ammeter is negligible, what are $(a)$ the emf of the battery and $(b)$ the current through the starting motor when the lights are on?

A solenoid $95.6 \mathrm{~cm}$ long has a radius of $1.90 \mathrm{~cm}$, a winding of 1230 turns, and carries a current of $3.58 \mathrm{~A}$. Calculate the strength of the magnetic field inside the solenoid.

At a location in the Philippines, the Earth's magnetic field has a value of $39.0 \mu \mathrm{T}$ and is horizontal and due north. The net field is zero $8.13 \mathrm{~cm}$ above a long, straight, horizontal wire that carries a steady current. (a) Calculate the current and (b) find its direction.