An electron is travelling at speed v in a straight line in a vacuum. It enters a uniform magnetic field of flux density 8.0 × 10⁻⁴ T. Initially, the electron is travelling at right angles to the magnetic field, as illustrated in Fig. 9.1. The path of the electron in the magnetic field is an arc of a circle of radius 6.4 cm. A uniform electric field is now applied in the same region as the magnetic field. The electron passes undeviated through the region of the two fields, as illustrated in Fig. 9.2. [Figure 9.1] [Figure 9.2]

Q: What topic does this question test?

This question tests Magnetic fields in A-Level Physics (syllabus code 9702). It is worth 10 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics May/June 2020 examination, Paper 4 Variant 2 (9702_s20_qp_42.pdf).

Question

An electron is travelling at speed v in a straight line in a vacuum. It enters a uniform magnetic field of flux density 8.0 × 10⁻⁴ T. Initially, the electron is travelling at right angles to the magnetic field, as illustrated in Fig. 9.1. The path of the electron in the magnetic field is an arc of a circle of radius 6.4 cm. A uniform electric field is now applied in the same region as the magnetic field. The electron passes undeviated through the region of the two fields, as illustrated in Fig. 9.2. [Figure 9.1] [Figure 9.2]

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