A LevelPhysicsOCRExam Questions6. Particles & Medical PhysicsMagnetic Fields

Magnetic Fields (OCR A Level Physics): Exam Questions

Exam code: H556

23 mins8 questions

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Magnetic Fields

1a
2 marks

The diagram below shows the top-view of a long current-carrying wire. wire

q19a-paper-2-nov-2021-ocr-a-level-physics

The direction of the current in the wire is into the plane of the paper.

Draw at least three field lines to indicate the magnetic field pattern around this wire.

[2]

How did you do?

1b
4 marks

The arrangement shown in the diagram below is used to determine the magnetic flux density between the poles of a permanent magnet.

q19b-paper-2-nov-2021-ocr-a-level-physics

The magnet is placed on the digital balance. The current-carrying wire is horizontal and at right angles to the magnetic field between the poles of the magnet. The wire is fixed.

The following results are collected.

  • length of the wire in the uniform field of the magnet = 6.0 ± 0.2 cm

  • balance reading with no current in wire = 80.0 g

  • balance reading with current in wire = 82.2 g

  • current in wire = 5.0 ± 0.1 A

Calculate the magnetic flux density B, including the absolute uncertainty. Ignore the absolute uncertainty in the balance readings. Write your value for B to 2 significant figures and the absolute uncertainty to 1 significant figure.

B = ................................... ± ............... T [4]

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2a
2 marks

Fig. 20.1 shows two horizontal parallel metal plates in a vacuum. The plates are connected to a high voltage d.c. supply.

Fig. 20.1

Two parallel horizontal plates. The top plate is labelled +V and the bottom plate is labelled 0 V.

On Fig. 20.1, draw at least five electric field lines to represent the uniform electric field between the plates.

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2b
2 marks

An ion with charge +q and mass m enters the region between the plates. The electric field strength is E.

Write an expression for the acceleration a of the ion while it is between the plates.

Give your answer in terms of E, q, and m.

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2c
4 marks

The ion leaves the electric field and enters a region of uniform magnetic field of flux density B.

The direction of the magnetic field is perpendicular to the velocity v of the ion.

(i) Explain why the path of the ion in the magnetic field is circular.

[2]

(ii) Show that the radius r of the circular path is given by the equation:

r space equals space fraction numerator m v over denominator B q end fraction

[2]

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2d
3 marks

This arrangement is used as a mass spectrometer to separate two isotopes of uranium, uranium-235 open parentheses scriptbase text U end text end scriptbase presuperscript 235 close parentheses and uranium-238 open parentheses scriptbase text U end text end scriptbase presuperscript 238 close parentheses.

Both isotopes are singly ionised and enter the magnetic field with the same velocity.

Compare the paths of the two isotopes and explain how this allows them to be separated.

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