An electron enters the uniform electric field between two horizontal parallel plates with an initial horizontal velocity. The upper plate is positive and the lower plate is negative. The potential difference between the plates is $480\ \text{V}$ and their separation is $24\ \text{mm}$.

A proton of speed $2.4 \times 10^{6}\ \text{m s}^{-1}$ enters a region of uniform magnetic field of flux density $0.32\ \text{T}$. The velocity of the proton is perpendicular to the magnetic field, which is directed into the page.

Positive ions pass through a velocity selector. The ions move horizontally to the right through a uniform electric field of strength $6.0\times10^{4}\ \text{V m}^{-1}$ directed upwards and a uniform magnetic field of flux density $0.20\ \text{T}$ directed out of the page.

Two long parallel wires are separated by $4.0\ \text{cm}$. The currents in the wires are $12\ \text{A}$ and $8.0\ \text{A}$ in the same direction.

A proton is accelerated from rest through a potential difference of $2.00\ \text{kV}$ in a vacuum. After acceleration it enters a second uniform electric field directed opposite to its velocity.

Electrons enter a uniform electric field between two horizontal parallel plates with initial horizontal speed $3.0 \times 10^6\ \text{m s}^{-1}$. The vertical deflection $s_y$ is measured for different lengths $X$ of the field region. The initial vertical velocity of the electrons is zero.

A proton enters a region of uniform magnetic field at point P. The magnetic field is directed into the plane of the page. The proton follows the circular path shown.

A beam of singly charged positive ions passes through perpendicular uniform electric and magnetic fields. The electric field strength is $7.2 \times 10^4\ \text{V m}^{-1}$. The vertical deflection of the beam is recorded for different ion speeds.

Electrons are accelerated from rest through a potential difference $V$ and then enter a uniform magnetic field at right angles to the field. The path in the magnetic field is circular. In one experiment, $V=250\ \text{V}$, $B=3.0\ \text{mT}$ and the radius of the path is $18\ \text{mm}$.

A singly charged positive ion of mass $6.64\times10^{-27}\ \text{kg}$ enters a uniform magnetic field of flux density $0.12\ \text{T}$ with speed $4.0\times10^{5}\ \text{m s}^{-1}$. The velocity of the ion makes an angle of $35^\circ$ with the direction of the magnetic field.

In a mass spectrometer, singly charged positive ions first pass undeflected through a velocity selector. The electric field in the selector is $1.8\times10^{5}\ \text{V m}^{-1}$ and the magnetic field is $0.30\ \text{T}$. The ions then enter a second region containing only a uniform magnetic field of flux density $0.50\ \text{T}$, where their circular path has radius $0.125\ \text{m}$.

In an investigation of the force on a current-carrying conductor, a straight wire of length $0.080\ \text{m}$ is held perpendicular to a uniform magnetic field. The force on the wire is measured for different currents. The best-fit gradient of the graph of force against current is $2.40\times10^{-3}\ \text{N A}^{-1}$.

A straight horizontal wire of length $5.0\ \text{cm}$ is placed at right angles to a uniform magnetic field. The wire is connected to a variable current supply and the magnetic force on the wire is measured using a balance.

Two long parallel wires carry equal currents in the same direction. The force per unit length on one wire is measured for different separations $r$.

Positive ions of speed $4.0 \times 10^5\ \text{m s}^{-1}$ move through a uniform magnetic field of strength $0.25\ \text{T}$. The angle $\theta$ between the ion velocity and the magnetic field is varied.

Two long vertical wires are separated by $25\ \text{mm}$. Each wire carries a current of $15\ \text{A}$ upwards. At the location of the experiment, the horizontal component of Earth's magnetic field is $50\ \mu\text{T}$.

Electrons are accelerated from rest through a potential difference $V$ and then enter a uniform magnetic field of strength $1.50\ \text{mT}$ at right angles. Their circular path radius $r$ is measured in a fine-beam tube.

A mass spectrometer uses a velocity selector followed by a region containing only a uniform magnetic field. Singly charged positive ions pass undeflected through the selector and then strike a detector at two positions, A and B. The electric field in the selector is $2.40 \times 10^4\ \text{V m}^{-1}$ and the magnetic field in the selector is $0.120\ \text{T}$. The magnetic field in the analyser region is $0.150\ \text{T}$.

Alpha particles enter a uniform magnetic field at an angle to the field direction and follow a helical path. The magnetic field strength is $0.50\ \text{T}$. For an alpha particle, $q = 3.20 \times 10^{-19}\ \text{C}$ and $m = 6.64 \times 10^{-27}\ \text{kg}$.

In a velocity-selector experiment, the magnetic field in the selector is fixed at $0.080\ \text{T}$ while the electric field strength is varied. The ions then enter an analyser region where a magnetic field of strength $0.200\ \text{T}$ bends the transmitted beam to a detector.

An electron enters midway between two horizontal parallel metal plates with horizontal speed $2.4\times 10^7\ \text{m s}^{-1}$. The potential difference between the plates is $420\ \text{V}$ and their separation is $4.0\ \text{cm}$. The uniform-field region has length $8.0\ \text{cm}$. The upper plate is positive.

A proton enters a uniform magnetic field of flux density $0.12\ \text{T}$ with speed $3.0\times 10^6\ \text{m s}^{-1}$. The velocity is perpendicular to the field, which is directed out of the plane of the page.

A straight wire of length $5.5\ \text{cm}$ is placed at right angles to a uniform magnetic field of flux density $0.35\ \text{T}$. The wire is connected to a power supply and rests between the poles of a magnet on a sensitive balance. The current in the wire is $4.2\ \text{A}$.

Two long straight parallel wires are separated by a fixed centre-to-centre distance of $4.0\ \text{cm}$. The currents are varied and the force per unit length is measured. The product of the currents is $I_1I_2$.

An electron travels parallel to a long straight wire carrying a steady conventional current of $60\ \text{A}$ upwards. At the instant shown, the electron is $2.0\ \text{cm}$ to the right of the wire and has speed $3.0 \times 10^6\ \text{m s}^{-1}$ upwards. Use $e = 1.60 \times 10^{-19}\ \text{C}$ and $\mu_0 = 4\pi \times 10^{-7}\ \text{N A}^{-2}$.

A beam of singly charged positive ions passes through a velocity selector. The uniform electric field has magnitude $1.8\times 10^4\ \text{V m}^{-1}$ and is directed vertically downward. A uniform magnetic field of magnitude $7.5\times 10^{-3}\ \text{T}$ is perpendicular to the page. Ions enter the selector horizontally from left to right.

Two long straight parallel wires, $A$ and $B$, are separated by $2.5\ \text{cm}$. Wire $A$ carries a current of $12\ \text{A}$ and wire $B$ carries a current of $8.0\ \text{A}$. The currents are initially in the same direction. A length $0.75\ \text{m}$ of wire $B$ is in the uniform central region of the apparatus.

A beam of ions is accelerated from rest through a potential difference of $1.20\ \text{kV}$ and then enters a uniform magnetic field of flux density $0.180\ \text{T}$ at right angles to the field. The circular path in the field has radius $6.5\ \text{cm}$.

Electrons are accelerated from rest through a potential difference of $2.5\ \text{kV}$ and then enter a uniform magnetic field of flux density $2.0\times 10^{-3}\ \text{T}$. The angle between the electron velocity and the magnetic field is $30^\circ$.

A charged particle leaves a visible track in a cloud chamber placed in a uniform magnetic field of flux density $0.45\ \text{T}$ directed into the page. At one point the particle speed is estimated as $4.5\times 10^6\ \text{m s}^{-1}$ and the radius of curvature of the track is $7.5\ \text{cm}$. The initial velocity at this point is to the right and the track curves upward.

Three long parallel wires $A$, $C$ and $B$ are perpendicular to the page and lie on a straight horizontal line. Wire $C$ is between $A$ and $B$, $4.0\ \text{cm}$ from $A$ and $8.0\ \text{cm}$ from $B$. Wires $A$ and $B$ carry currents out of the page of $9.0\ \text{A}$ and $12\ \text{A}$ respectively. Wire $C$ carries a current of $5.0\ \text{A}$ into the page.

A rectangular coil has $20$ turns. Each vertical side of the coil has length $4.0\ \text{cm}$ and lies in a uniform magnetic field of flux density $0.60\ \text{T}$. A current of $1.5\ \text{A}$ flows in the coil. The current in one vertical side is upward and in the other vertical side is downward.

A Bainbridge mass spectrometer uses a velocity selector followed by a uniform magnetic-field analyser. In the selector, $E=6.0\times 10^3\ \text{V m}^{-1}$ and $B=3.0\times 10^{-2}\ \text{T}$. Singly charged carbon ions then enter an analyser field of flux density $8.0\times 10^{-2}\ \text{T}$ at right angles to the field.

An alpha particle of charge $+3.20\times10^{-19}\ \text{C}$ and mass $6.64\times10^{-27}\ \text{kg}$ enters a region of crossed uniform fields. The electric field has magnitude $4.8\times10^4\ \text{V m}^{-1}$ and is directed upward. The magnetic field has magnitude $2.0\times10^{-2}\ \text{T}$ and is directed out of the page. The particle enters horizontally from left to right with speed $1.8\times10^6\ \text{m s}^{-1}$. The length of the field region is $12\ \text{cm}$.