A wire carrying a current is placed at right angles to a uniform magnetic field of magnetic flux density$B$. When the current in the wire is / , the magnetic force that acts on the wire is $F$.

What is the force on the wire, placed in the same orientation, when the magnetic field strength is$2B$ and the current is $\frac{1}{4}$$?$

A  $\frac{F}{4}$  B $\frac{F}{2}$  C $F$   D $2F$

There is an electric current in a wire of mass per unit length$40 g{m}^{-1}$• The wire is placed in a magnetic field of strength $0.50$ T and the current is gradually increased until the wire just lifts off the ground. What is the value of the current when this happens?

$\left(a\right) 0.080A$

$\left(b\right) 0.20A$

$\left(c\right) 0.78 A$

$\left(d\right) 780A$

A current-carrying wire is placed in a uniform magnetic field.

(a) Describe how the wire should be placed to experience the
maximum force due to the magnetic field.

A current-carrying wire is placed in a uniform magnetic field.

(b) Describe how the wire should be placed to experience no force due to the magnetic field .

A current-carrying conductor placed at right angles to a uniform magnetic field experiences a force of$4.70\times {10}^{-3}N.$ Determine the force on the wire when, separately:

(a) the current in the wire is increased by a factor of$3.0$

A current-carrying conductor placed at right angles to a uniform magnetic field experiences a force of$4.70\times {10}^{-3}N.$ Determine the force on the wire when, separately:

(c) the length of the wire in the magnetic field is reduced to $40\%$
of its original length.

A copper wire carrying a current of $1.2A$ has $3.0cm$ of its length placed in a uniform magnetic field, as shown.

The force experienced by the wire is$3.8\times {10}^{-3}N$when the angle between
the wire and the magnetic field is$50°.$

(b) State the direction of the force experienced by the wire.

This diagram shows a view from above of two long, parallel strips of aluminium foil, A and B, carrying a current downwards into the paper.

(b) State and explain the direction of the forces caused by the current in the strips.

This diagram shows a wire $XY$ that carries a constant direct current. Plotting compass $R$, placed alongside the wire, points due north. Compass $P$ is placed below the wire and compass $Q$ is placed above the wire.

(a) State the direction of the current in the wire.