A simplified model of a mass spectrometer uses a velocity selector to ensure ions enter a uniform magnetic field with a consistent speed. Potassium ions ($^{39}K^+$) are produced in an ion source and accelerated through a potential difference of 500 V. After exiting the accelerating region, the ions pass through a region with both an electric field of 2.0 × 10$^4$ V/m and a magnetic field, oriented such that only ions with a specific velocity pass through undeflected. These selected ions then enter a second region containing only a uniform magnetic field of 0.15 T, where they are deflected in a circular path before striking a detector.
b. Determine the magnitude of the magnetic field in the velocity selector that will allow the potassium ions (with the speed calculated in part a) to pass through undeflected, given the electric field is 2.0 × 10$^4$ V/m. In what direction must the magnetic field be oriented relative to the electric field and the velocity of the ions?
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Create Free Account Log inThis is a free VCE Units 3 & 4 Physics practice question worth 3 marks, testing your understanding of Magnetic field & particles. It falls under How do things move without contact? in Unit 3: How do fields explain motion and electricity?. Submit your answer above to receive instant AI-powered marking and personalised feedback.
In this unit students use Newton’s laws to investigate motion in one and two dimensions. They explore the concept of the field as a model used by physicists to explain observations of motion of objects not in apparent contact. Students compare and contrast three fundamental fields – gravitational, magnetic and electric – and how they relate to one another. They consider the importance of the field to the motion of particles within the field. Students examine the production of electricity and its delivery to homes. They explore fields in relation to the transmission of electricity over large distances and in the design and operation of particle accelerators. A student-designed practical investigation involving the generation of primary data and including one continuous, independent variable related to fields, motion or light is undertaken either in Unit 3 or Unit 4, or across both Units 3 and 4, and is assessed in Unit 4, Outcome 2. The design, analysis and findings of the investigation are presented in a scientific poster format.
In this area of study, students examine the similarities and differences between three fields: gravitational, electric and magnetic. Students explore how positions in fields determine the potential energy of, and the force on, an object. They investigate how concepts related to field models can be applied to construct motors, maintain satellite orbits and to accelerate particles including in a synchrotron.
Analyse the use of a magnetic field to change the path of a charged particle, including: • the magnitude and direction of the force applied to an electron beam by a magnetic field: F = qvB, in cases where the directions of v and B are perpendicular or parallel • the radius of the path followed by an electron in a magnetic field: r = mv / (qB), where v << c.
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