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]

1. (a)(i)State and explain the direction of the magnetic field.[2]
2. (a)(ii)Show that the speed v of the electron is 9.0 × 10⁶ m s⁻¹.[3]
3. (b)(i)On Fig. 9.2, mark with an arrow the direction of the uniform electric field.[1]
4. (b)(ii)Use data from (a) to calculate the magnitude of the electric field strength.[2]
5. (c)The electron in (b) is now replaced by an α-particle travelling at the same speed v along the same initial path as the electron. Describe and explain the shape of the path in the region of the magnetic and electric fields.[2]

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