Physics

Three wires carry currents, as shown in the following scale diagram.

How many of the wires experience a net force to the left?
A. $0$
B. $1$
C. $2$
D. $3$

Two horizontal metal rods, A and B, of different materials are resting on a frictionless table. Initially they are at rest in position 1. Both rods are then connected to a battery using wires. After the switch is turned on, currents of different magnitude flow in each rod. The rods move to position 2 after time, t. In position 2, B has a larger displacement than A from position 1. The masses of the wires are negligible.
When the switch is turned on, the current in rod A is greater than the current in rod B.
Consider this statement.
Position 2 results from the larger current in rod A, causing a larger force to act on rod B.
Evaluate this statement with reference to relevant physics principles.

Two horizontal metal rods, A and B, of different materials are resting on a frictionless table. Initially they are at rest in position 1.
Both rods are then connected to a battery using wires. After the switch is turned on, currents of different magnitude flow in each rod. The rods move to position 2 after time, t. In position 2, B has a larger displacement than A from position 1. The masses of the wires are negligible.

Position 1 is reproduced below. Draw wires to show how the battery must be connected to the ends of the two rods in order for the magnitude of the current in each rod to be different, and for position 2 to be reached. No components, other than the wires, are required.

A short copper rod $R$ is placed on a pair of thick horizontal parallel copper rails. A horizontal magnetic field exists in the direction shown by the dashed arrows. The diagram shows the apparatus when viewed from directly above.

When switch $S$ is closed, $R$ will tend to:
(A) Lift upwards away from the rails.
(B) Move to the left.
(C) Move to the right.
(D) Be pressed downwards onto the rails.

An investigation was performed with the aim of measuring the value of the magnetic permeability constant, $\mu_0$.

Two wires, both of length $70.0\ \mathrm{cm}$, were arranged horizontally, with one wire above the other, as shown in the diagram below. The bottom wire is resting on an electronic balance.

When a current of $25.5\ \mathrm{A}$ flows through both wires, the reading on the electronic balance changes by $0.500\ \mathrm{g}$.

What is the value of $\mu_0$ as determined by this investigation?
(A) $3.4\times10^{-7}$
(B) $1.7\times10^{-7}$ (C) (D)

An investigation was performed with the aim of measuring the value of the magnetic permeability constant, $\mu_0$.

Two wires, both of length $70.0\ \mathrm{cm}$, were arranged horizontally, with one wire above the other, as shown in the diagram below. The bottom wire is resting on an electronic balance.

When a current of $25.5\ \mathrm{A}$ flows through both wires, the reading on the electronic balance changes by $0.500\ \mathrm{g}$.

Which measurement made in the above investigation has the greatest relative error?
(A) length of the wires
(B) separation of the wires
(C) current in wires
(D) change in the reading of the electronic balance

A rectangular coil has dimensions $3.0\ \mathrm{cm}\times4.0\ \mathrm{cm}$ and carries a current of $15.0\ \mathrm{mA}$ in a uniform magnetic field of $3.0\ \mathrm{T}$. The coil has 20 turns of wire and is free to rotate about the axis as shown.

If the coil is rotated by $25^\circ$, what is the torque acting on the coil?
(A) $9.79\times10^{-4}\ \mathrm{N\,m}$ clockwise
(B) $9.79\times {10}^{}$ anticlockwise (C) clockwise (D) anticlockwise