A flat circular loop is held in a uniform magnetic field. A student states that the magnetic flux is greatest when the plane of the loop is parallel to the field.

A coil has $150$ turns. The magnetic flux through each turn changes uniformly from $3.2\times10^{-4}\ \text{Wb}$ to $0.80\times10^{-4}\ \text{Wb}$ in a time of $0.12\ \text{s}$.

A switch is used to connect a coil to a cell. The current in the coil increases from zero to a steady value.

A small generator is easier to rotate when its external circuit is open than when a lamp is connected and glowing.

A rectangular coil of $80$ turns and area $2.5\times10^{-3}\ \text{m}^2$ rotates at constant angular speed in a uniform magnetic field of flux density $0.60\ \text{T}$. The angular speed is $120\ \text{rad s}^{-1}$.

The rotation frequency of an ac generator is doubled. The coil, magnetic field strength and coil area are unchanged.

A flat search coil of area $2.0 \times 10^{-2}\ \text{m}^2$ is placed in a uniform magnetic field. The angle $\theta$ is measured between the normal to the coil and the magnetic field. The graph shows how the magnetic flux $\Phi$ through one turn varies with $\cos\theta$.

A coil is connected in series with a switch and a direct-current power supply. The graph shows the current in the coil when the switch is closed and later opened.

A rectangular conducting loop is pulled at constant speed through a region of uniform magnetic field directed into the page. At the instant considered, the whole loop is entirely inside the uniform field region.

A bar magnet is moved towards a coil connected to a sensitive galvanometer. The north pole of the magnet faces the coil.

A coil rotates at constant angular speed in a uniform magnetic field. At one instant the magnetic flux linkage through the coil is maximum.

The graph shows the magnetic flux linkage $N\Phi$ for a coil connected to a high-resistance voltmeter during a switching process.

A stationary circular coil of $80$ turns and area $3.0 \times 10^{-3}\ \text{m}^2$ is placed with its plane perpendicular to a uniform magnetic field. The graph shows how the magnetic flux density varies with time as the field is switched on and later held constant.

A conducting rod moves at right angles to a uniform magnetic field on two parallel conducting rails. The field has magnetic flux density $0.18\ \text{T}$. The table shows the emf induced across the rod for different speeds.

A bar magnet is moved along the axis of a coil connected to a centre-zero galvanometer. The annotated stimulus gives the magnet pole facing the coil, the direction of motion and the sign convention for the galvanometer deflection.

An aircraft flies horizontally through Earth’s magnetic field. The annotated plan view shows the wingspan and the components of Earth’s magnetic field at the aircraft’s location. The vertical component is perpendicular to the plane of the page.

A generator coil produces a sinusoidal emf with peak value $18\ \text{V}$ at a rotation frequency of $25\ \text{Hz}$. The coil is then rotated at $40\ \text{Hz}$ with all other factors unchanged.

A rectangular coil is pulled at constant speed into, through and out of a region of uniform magnetic field. The graph shows the magnetic flux linkage $N\Phi$ through the coil as a function of time.

A rectangular coil rotates at constant angular speed in a uniform magnetic field. The graph shows the magnetic flux linkage $N\Phi$ through the coil for one rotation.

A laboratory ac generator uses the same coil and magnetic field at several rotation frequencies. The graph shows the measured peak emf $\varepsilon_0$ as a function of rotation frequency $f$.

A small generator is driven at constant angular speed while different resistive loads are connected. The graph shows the additional driving torque required above the no-load torque as the load current changes.

A rectangular coil of 120 turns rotates at constant angular speed in a uniform magnetic field. The coil has sides $4.0\ \text{cm}$ and $6.0\ \text{cm}$. The magnetic flux density is $0.85\ \text{T}$. At $t=0$, the normal to the coil is parallel to the magnetic field.

A coil of 250 turns and area $1.8\times10^{-3}\ \text{m}^2$ is placed with its plane perpendicular to a uniform magnetic field. The magnetic flux density is varied uniformly from $0$ to $0.60\ \text{T}$ in $0.12\ \text{s}$ and then kept constant.

An aircraft flies horizontally due east at $230\ \text{m s}^{-1}$. The vertical component of Earth's magnetic flux density at this location is $4.8\times10^{-5}\ \text{T}$ directed downward. The distance between the wingtips is $38\ \text{m}$.

A coil is connected to a battery through a switch and to a sensitive voltmeter that can detect the emf across the coil itself. The switch is first closed and then, after a long time, opened.

The same coil is rotated in the same uniform magnetic field at two different constant frequencies. The graph shows the induced emf against time for both runs.

A conducting rod of length $0.18\ \text{m}$ slides without friction on two horizontal conducting rails. The rails are connected to a $4.5\ \Omega$ resistor. A uniform magnetic field of flux density $0.72\ \text{T}$ is directed into the plane of the page. The rod is pulled to the right at constant speed $1.6\ \text{m s}^{-1}$.

A rectangular coil of 60 turns and resistance $12\ \Omega$ moves at constant speed into a region of uniform magnetic field. The coil has width $3.0\ \text{cm}$, measured in the direction of motion, and height $5.0\ \text{cm}$. The field has flux density $0.40\ \text{T}$ and is directed out of the page. The speed of the coil is $0.20\ \text{m s}^{-1}$.

A strong bar magnet is released above a fixed horizontal conducting ring. The north pole of the magnet faces the ring as it falls through the ring. Air resistance is negligible.

A small wind-turbine generator contains a coil rotating in a uniform magnetic field. The output is connected to a lamp. When the lamp is disconnected, the turbine turns faster in the same wind.

A single square loop of side $8.0\ \text{cm}$ is in a uniform magnetic field of flux density $0.30\ \text{T}$. The loop is rotated from a position where its normal is parallel to the field to a position where its plane is parallel to the field in $0.040\ \text{s}$.

A rectangular coil rotates in a uniform magnetic field. The magnetic flux linkage is given by

$N\Phi=NBA\cos(\omega t).$

The coil is connected to an oscilloscope that displays the induced emf against time.

A metal rod of mass $0.060\ \text{kg}$ and length $0.25\ \text{m}$ falls vertically while maintaining contact with two vertical conducting rails. The rails are connected at the top by a resistor of resistance $3.0\ \Omega$. A uniform magnetic field of flux density $0.50\ \text{T}$ is perpendicular to the plane of the rails. The resistance of the rails and rod is negligible.

An AC generator supplies a local grid that must remain at $50\ \text{Hz}$. The generator uses coils rotating in a magnetic field. Engineers need to increase the rms output voltage without changing the grid frequency.