Topic 4.3: Motion in Electromagnetic Fields Questions

A small charged sphere is held at rest in a uniform electric field.

State the formula for the electric force on the sphere, and state how the direction of this force compares with the field direction if the charge is negative.

An ion carrying charge 1.6 × 10⁻¹⁹ C moves at 5.0 × 10⁶ m s⁻¹ at right angles to a magnetic field of strength 0.30 T.

Calculate the magnitude of the magnetic force on the ion.

A straight wire of length 0.30 m lies at right angles to a uniform magnetic field of flux density 0.45 T and carries a current of 8.0 A.

Calculate the magnitude of the force on the wire.

State the equation for the magnitude of the force on a straight current-carrying conductor in a magnetic field, and define each symbol in it.

A charged particle is held stationary in a uniform magnetic field.

State the size of the magnetic force acting on it, and explain your answer.

A straight horizontal wire of length 0.15 m lies at right angles to a uniform magnetic field.

When it carries a current of 2.0 A the force on it is 0.090 N.

When the current is increased to 6.0 A (everything else unchanged), state the new force, and calculate the magnetic field strength B.

An electron (charge 1.6 × 10⁻¹⁹ C, mass 9.1 × 10⁻³¹ kg) is placed in the uniform field between two parallel plates, where the field strength is 4.0 × 10³ N C⁻¹.

A straight wire of length 0.50 m lies at right angles to a uniform magnetic field.

The current in the wire is steadily increased from 2.0 A to 6.0 A, and the magnetic force on the wire is observed to increase from 0.30 N to 0.90 N.

What is the magnetic field strength?

A straight horizontal wire of length 0.25 m lies in an east–west direction and carries a current of 4.0 A flowing towards the east. The wire sits in a uniform magnetic field of magnitude 0.30 T that points horizontally towards the north.

What is the magnitude and direction of the magnetic force on the wire?

A straight metal rod rests across two horizontal parallel rails separated by 0.25 m.

A uniform magnetic field of magnitude 0.40 T is directed out of the page in the region of the rod.

A 3.0 A current is supplied to the rails, and the rod is observed to begin moving to the right (in the plane of the page).

What is the direction of the current in the rod, and the magnitude of the initial force on it?

Two parallel plates are separated by 0.040 m and connected to a 600 V supply, producing a uniform field between them.

A horizontal wire passes through the gap of a horseshoe magnet, with the magnetic field directed horizontally from the north pole to the south pole.

The current in the wire flows horizontally and at right angles to the field.

Deduce the direction of the force on the wire, and describe how the force changes if the wire is rotated until the current flows along the field direction.

Explain why a straight current-carrying wire experiences no force when it is placed so that the current flows parallel to the magnetic field.

A wire of length 0.080 m carries a current of 2.5 A at right angles to a magnetic field of flux density 0.60 T.

In the same uniform field, a proton and an electron each experience an electric force of the same magnitude.

Explain why the electron has a much larger acceleration than the proton, and estimate roughly how many times larger it is.

A 0.40 m length of wire carries a current of 6.0 A through a uniform magnetic field of strength 0.25 T.

The current makes an angle of 30° with the field direction.

Calculate the force on the wire.

A velocity selector has parallel plates 2.0 cm apart with a potential difference of 600 V across them, and a magnetic field of 0.15 T crossed at right angles.

Show that the speed selected by this device is about 2 × 10⁵ m s⁻¹.

A metal rod rests on two horizontal rails and carries a current flowing from the left rail to the right rail.

A uniform magnetic field points vertically downward, into the plane of the rails.

Use Fleming's left-hand rule to determine the direction of the force on the rod, and state what happens to that direction if the current is reversed.

In a demonstration of the motor effect, a wire experiences a maximum force of 0.40 N when it carries a current of 5.0 A at right angles to a uniform magnetic field of strength 0.20 T.

Calculate the length of wire that lies within the field.

A charged particle moving horizontally enters the gap between two charged parallel plates and is deflected so that it follows a curved path.

Outline why this path is a parabola, referring to the motion along the plates and the motion across the field.