Magnetic Fields (Edexcel International A Level (IAL) Physics): Exam Questions

A carriage on a roller coaster ride travels along a horizontal track towards a vertical tower, as shown.

The carriage starts from rest. A force of 109 kN acts on the carriage for 2.9 s. The carriage then moves up a vertical tower of height 81 m.

i) Show that the velocity of the carriage is about 40 m s^–1 as it leaves the horizontal track.

total mass of carriage and people = 7500 kg

(2)

ii) Deduce whether this velocity is enough for the carriage to reach the top of the tower.

Assume that resistive forces are negligible.

(3)

Just before the carriage reaches the end of the ride it is slowed by an electromagnetic brake. Powerful magnets are attached to the track. An aluminium fin is attached to the carriage. The fin moves through a narrow gap between the magnets.

 Explain why the fin will leave the gap with a much slower speed than it entered the gap.

Faraday’s law can be written as $\xi =\frac{-d\left(N\varphi \right)}{dt}$

State the name of the term $N\varphi$ and its unit.

A coil of 500 turns and radius 3.0 mm is placed between two poles of an electromagnet as shown. The terminals are connected to an a.c. power supply.

The magnetic flux density B perpendicular to the plane of the coil varies with time t as shown below.

Determine the maximum e.m.f. across the coil.

Maximum e.m.f. = ..............................

Some electric motor designs rely on electromagnetic induction.

A laboratory demonstration of the principle of an induction motor is shown.

An aluminium disc is free to rotate and is initially stationary. A powerful magnet is moved around the disc in the direction of the arrow, without touching the disc.

A student suggests that the disc will start to rotate as the magnet is moved and that the disc will rotate in the same direction as the movement of the magnet.

Discuss this suggestion.

In 1821, Michael Faraday made what is believed to be the first electric motor.

The stiff wire was suspended freely from a stand. The mercury completed an electrical circuit, which included the wire. When there was a current in the wire, the wire moved around the magnet.

The wire made 10 complete revolutions around the magnet in a time of 8.3 s.    

Calculate the angular velocity of the wire.

Angular velocity = .....................................

When the current in the wire is 1.1 A, the wire is at an angle of 10° to the vertical. 

The length of the wire in the horizontal magnetic field is 3.5 cm.

Determine the force on the wire. 

magnetic flux density = 0.053 T

Magnitude of force on wire = .......................................

Direction of force on wire = ......................................

A student sets up the apparatus shown to investigate the force on a rigid wire in a uniform magnetic field of flux density $B$.

A plan view of the apparatus is also shown.

With the switch open, the balance is zeroed. When the switch is closed, the reading on the balance increases.

Deduce the direction of the magnetic field. You may add to the diagram.

When the reading on the ammeter was $3.25\text{ A}$, the balance reading increased by $6.285\text{ g}$. The length $l$ of wire in the magnetic field was $4.5\text{ cm}$.

Calculate the magnetic flux density $B$ in the region between the magnets.

The resolution of the balance was $0.001\text{ g}$.

$l$ was measured with a metre rule of resolution $1\text{ mm}$.

The percentage uncertainty in the ammeter reading was $0.3\%$.

Assess which of these measurements was the most significant source of uncertainty in the measured value of $B$.