Charged particles in magnetic fields

Suggest why the magnetic force acting on the proton has a different magnitude at X than at Y

At X, the motion of the proton is instantaneously equivalent to motion in a circle at a constant speed.

Calculate the radius of this circular motion.

1 Calculate the magnitude of the resultant force on the proton at Y.

2 Explain why the motion of the proton at Y is not instantaneously equivalent to motion in a circle at a constant speed.

A particle is moving at right angles to a uniform magnetic field of flux density B. The particle has mass m, charge q and moves in a circular arc of radius r in the region of the magnetic field.

What quantities are required to determine the momentum of this particle?

A B, q and r

B B, q and m

C B, q, r and m

D q, r and m

Your answer

In beta-plus decay, a proton decays into three other particles.

Write a nuclear equation for this process.

Fig. 24 shows two horizontal metal plates in a vacuum.

The diagram is not drawn to scale. Electrons travelling horizontally enter the space between the charged plates and are deflected vertically.

The potential difference between the plates is 4000 V. The distance between the plates is 0.08 m. The initial speed of the electrons is 6.0 × 10⁷ m s^–1. The vertical deflection of the electrons at the far end of the plates is x.

The length of each plate is 0.12 m.

Show that the time t taken by the electron to travel this length is 2.0 × 10^–9 s.

Calculate the vertical deflection x of the electron.

The arrangement shown in Fig. 24 is now used to investigate positrons emitted from a radioactive source. The speed of the positrons is also 6.0 × 10⁷ m s^–1.

The initial path of the positrons is the same as that of the electrons in Fig. 24.

On Fig. 24, sketch the path of the positrons between the plates.

Beta-minus particles (electrons) emitted from a radioactive source have a range of speeds.

Describe and explain how a uniform magnetic field can be applied in the space between the charged plates to select beta-minus particles with a specific speed. No calculations are required.

Fig. 20 illustrates a device used to determine the relative abundance of charged rubidium ions.

A uniform magnetic field is applied to an evacuated chamber. The direction of the magnetic field is perpendicular to the plane of the paper.

A beam of positive rubidium ions enters the chamber through a hole at H. The ions travel in a semi-circular path in the magnetic field. The ions are detected at point D.

The chemical composition of ancient rocks found on the Earth can be used to estimate the age of the Earth. Nuclei of rubidium-87 (⁸⁷₃₇Rb) decay spontaneously into nuclei of strontium-87 (⁸⁷₃₈Sr). The half-life of rubidium-87 is 49 billion years.

Name the two leptons emitted in the decay of a rubidium-87 nucleus.

The percentage of rubidium left in a sample of an ancient rock is 95%.

Estimate the age of the Earth in billion years.

age =........ billion years

A charged particle moves in a circular path of radius 1.2 cm in a uniform magnetic field.

The direction of the magnetic field is perpendicular to the plane of the paper.

The particle has mass m, charge + Q and speed v.

Another particle of mass 3 m, charge +2 Q and speed v moves in a circular path of radius R in the same magnetic field.

What is the value of R ?

A 0.8 cm

B 1.2 cm

C 1.8 cm

D 7.2 cm

Your answer

An electron moves in a circle of radius 2.0 cm in a uniform magnetic field of flux density 170 mT.

What is the momentum of this electron?

Your answer

A beam of charged particles is not deflected when it passes through a region where both electric and magnetic fields are present.

Which statement is not correct?

A All the particles have the same speed.

B The resultant force on each particle is zero.

C The magnetic force is equal to the electric force on each particle.

D The magnetic field and the electric field are in the same direction.

Your answer