P.3.7.5.2 Moving charges in a magnetic field

Different magnetic fields are present in the two chambers shown. A particle enters the first chamber at a velocity of 80 m s^–1 and is deflected into a circular path of radius 200 mm.

In the second chamber it follows a circular path of radius 100 mm

The particle leaves the second chamber at a speed of

• 20 m s^–1

• 40 m s^–1

• 80 m s^–1

• 160 m s^–1

Two charged particles, P₁ and P₂, follow circular paths as they move at right angles to the same uniform magnetic field. Both particles are travelling at the same speed.

The radius of the path travelled by P₁ is twice the radius of the path travelled by P₂.

The mass of P₁ is m and its charge is q.

What is the mass of P₂ and the charge of P₂?

• A

• B

• C

• D

Charged particles, each of mass m and charge Q, travel at a constant speed in a circle of radius r in a uniform magnetic field of flux density B.

Which expression gives the frequency of rotation of a particle in the beam?

• 
• 
• 
• 

Which one of the following statements is correct?

An electron follows a circular path when it is moving at right angles to

• a uniform magnetic field.

• a uniform electric field.

• uniform electric and magnetic fields which are perpendicular.

• uniform electric and magnetic fields which are in opposite directions.

Two electrons, X and Y, travel at right angles to a uniform magnetic field. X experiences a magnetic force, FX, and Y experiences a magnetic force, FY.

What is the ratio shown if the kinetic energy of X is half that of Y?

• 1/4

• 1/2

• 
  

  $\frac{1}{\sqrt{2}}$

• 1

The path followed by an electron of momentum p, carrying charge –e, which enters a magnetic field at right angles, is a circular arc of radius r.

What would be the radius of the circular arc followed by an α particle of momentum 2p, carrying charge +2e, which entered the same field at right angles?

• $\frac{r}{2}$

• r

• 2r

• 4r

Which line, A to D, in the table correctly describes the trajectory of charged particles which enter separately, at right angles, a uniform electric field, and a uniform magnetic field?

• A

• B

• C

• D

A beam of positive ions enters a region of uniform magnetic field, causing the beam to change direction as shown in the diagram.

What is the direction of the magnetic field?

• out of the page and perpendicular to it

• into the page and perpendicular to it

• in the direction indicated by +y

• in the direction indicated by -y

When a β particle moves at right angles through a uniform magnetic field it experiences a force F. An α particle moves at right angles through a magnetic field of twice the magnetic flux density with velocity one tenth the velocity of the β particle. What is the magnitude of the force on the α particle?

• 0.2 F

• 0.4 F

• 0.8 F

• 4.0 F

Charged particles, each of mass m and charge Q, travel at a constant speed in a circle of radius r in a uniform magnetic field of flux density B. Which expression gives the frequency of rotation of a particle in the beam?

• 
• 
• 
•