Fig. 1 shows a simplified magnetic field surrounding a rapidly rotating star. A science team uses this model to predict the path of charged particles in the...
Question 1 Report
Fig. 1 shows a simplified magnetic field surrounding a rapidly rotating star. A science team uses this model to predict the path of charged particles in the thin air-free region above the star. The arrows show the direction of the magnetic field. A proton enters the region at right angles to the field lines with a velocity of 2.4 × 106 m/s. At this point, the magnetic flux density is 0.30 T. The charge on a proton is 1.6 × 10−19 C.
(a) What is the name of the region around the star in which a magnetic force can act on the proton? [1]
(b) Describe the direction of the magnetic field at the position of the proton in Fig. 1. [2]
(c) Calculate the magnetic force on the proton. Use the equation:
force = magnetic flux density × charge × velocity
Give your answer in N. [3]
(d) Use ideas about forces to describe the proton’s path as it travels through a uniform magnetic field. [2]
Answer Details
A moving charged particle in a magnetic field experiences a force when it moves at right angles to the field. That force changes its direction, rather than simply increasing its speed.
- (a) The region is a magnetic field. [1]
- (b) At the proton, the field is towards the star, to the left [1], and is perpendicular to the proton's velocity. [1]
- (c) \[F=Bqv=0.30\times1.6\times10^{-19}\times2.4\times10^6\]
\[F=1.152\times10^{-13}\ \text{N}\] Therefore \(1.15\times10^{-13}\ \text{N}\), or \(1.2\times10^{-13}\ \text{N}\), is accepted. [3] - (d) The magnetic force acts at right angles to the proton's motion [1], so the proton follows a curved or circular path. [1]
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