Fields and their consequences (A-level only)

Question 8

This question is about using a digital balance to investigate the force on a wire placed in a magnetic field when there is an electric current in the wire.

A student carries out the following procedure:

A metre ruler is pivoted at the $cm5.0\text{ cm}$ mark and a prism is placed on a digital balance.
The free end of the ruler is raised, the balance is turned on, and then set to zero.
The ruler is then supported by the prism with the apex of the prism at the $cm30.0\text{ cm}$ mark. The height of the pivot is adjusted so that the ruler is horizontal. The balance now reads $g225.00\text{ g}$ .

Deduce the mass of the ruler. State one assumption you make.

[3]

The student then attaches a uniform wire to the upper edge of the ruler. The ends of the wire are connected to terminal blocks on the bench.

A horizontal uniform magnetic field is applied, perpendicular to the wire, between the $cm78.0\text{ cm}$ and $cm82.0\text{ cm}$ marks on the ruler.

The balance reading $M$ decreases linearly as the current $I$ in the wire increases.

At a current of $1.0\text{ A}$ , the balance reading is $g248.86\text{ g}$ .
At a current of $5.0\text{ A}$ , the balance reading is $g247.46\text{ g}$ .

It can be shown that $B$ , the magnitude of the magnetic flux density of the horizontal uniform magnetic field, is given by:

\frac{\sigma}{3L}

where:

$σ\sigma$ is the magnitude of the change in force acting on the prism per unit current in the wire.
$L$ is the length of the region where the magnetic field cuts through the wire.

Determine $B$ . Use $9.81\text{ m s}^{-2}$ .

[5]

Fields and their consequences (A-level only)

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Question 8

This question is about using a digital balance to investigate the force on a wire placed in a magnetic field when there is an electric current in the wire.

A student carries out the following procedure:

A metre ruler is pivoted at the $cm5.0\text{ cm}$ mark and a prism is placed on a digital balance.
The free end of the ruler is raised, the balance is turned on, and then set to zero.
The ruler is then supported by the prism with the apex of the prism at the $cm30.0\text{ cm}$ mark. The height of the pivot is adjusted so that the ruler is horizontal. The balance now reads $g225.00\text{ g}$ .

Deduce the mass of the ruler. State one assumption you make.

[3]

The student then attaches a uniform wire to the upper edge of the ruler. The ends of the wire are connected to terminal blocks on the bench.

A horizontal uniform magnetic field is applied, perpendicular to the wire, between the $cm78.0\text{ cm}$ and $cm82.0\text{ cm}$ marks on the ruler.

The balance reading $M$ decreases linearly as the current $I$ in the wire increases.

At a current of $1.0\text{ A}$ , the balance reading is $g248.86\text{ g}$ .
At a current of $5.0\text{ A}$ , the balance reading is $g247.46\text{ g}$ .

It can be shown that $B$ , the magnitude of the magnetic flux density of the horizontal uniform magnetic field, is given by:

\frac{\sigma}{3L}

where:

$σ\sigma$ is the magnitude of the change in force acting on the prism per unit current in the wire.
$L$ is the length of the region where the magnetic field cuts through the wire.

Determine $B$ . Use $9.81\text{ m s}^{-2}$ .

[5]

Fields and their consequences (A-level only)

Question 8

Markscheme

Fields and their consequences (A-level only)

Question 8

Markscheme

Fields and their consequences (A-level only)

Question 8

Fields and their consequences (A-level only) Questions

Fields and their consequences (A-level only)

Question 8

Fields and their consequences (A-level only) Questions