An electron beam is directed horizontally from left to right into the region between two horizontal parallel metal plates, AAA and BBB, where plate AAA is the upper plate and plate BBB is the lower plate. Plate AAA is maintained at a negative potential relative to plate BBB, creating a uniform vertical electric field.
To keep the path of the electrons horizontal and undeflected, a uniform magnetic field is applied in the region between the plates.
Direction of the Magnetic Field Determine the direction of the magnetic field required to allow the electron beam to pass undeflected. Explain your reasoning by reference to the forces acting on the electrons.
Adjustments for Higher Speed The speed of the electrons entering the region is now increased. Explain how the path of the electrons can be restored to a straight horizontal line by adjusting:
Include the relevant algebraic relationship for key variables.
Significance of the Specific Charge J.J. Thomson used a similar crossed-field apparatus to determine the specific charge (qm\frac{q}{m}mq) of cathode ray particles (electrons). Discuss the significance of his findings when comparing the specific charge of the electron to that of the hydrogen ion.
66 exam-style questions on AQA A Level Physics Magnetic fields (A-level only), covering Magnetic flux density (A-level only), Moving charges in a magnetic field (A-level only), Magnetic flux and flux linkage (A-level only), Electromagnetic induction (A-level only), Alternating currents (A-level only), and The operation of a transformer (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.