An electron in an old-style television picture tube moves toward the front of th

Question

An electron in an old-style television picture tube moves toward the front of the tube with a speed of 6.7 times 106 m/s along the x axis (see figure). Surrounding the neck of the tube are coils of wire that create a magnetic field of magnitude 0.025 T, directed at an angle of 60 degree to the x axis and lying in the xy plane. Calculate the magnetic force on the electron. Conceptualize Recall that the magnetic force on a charged particle is perpendicular to the plane formed by the velocity and magnetic field vectors. Use one of the right-hand rules to convince yourself that the direction of the force on the electron is downward in the figure. Categorize We evaluate the magnetic force using the magnetic version of the particle in a field model. Analyze Use the following equation to find the magnitude of the magnetic force: F_B = |q|vB sin theta = (1.6 times 10-19 C)(6.7 times 106 m/s)(0.025 T)(sin 60 degree) = N Finalize For practice using the vector product, evaluate this force in vector notation using F_B = qv times B. The magnitude of the magnetic force may seem small to you, but remember that it is acting on a very small particle, the electron. To convince yourself that this is a substantial force for an electron, calculate the initial acceleration of the electron due to this force. A proton moves with a speed of 3.00 times 10^6 m/s horizontally, at a right angle to a magnetic field. What magnetic field strength is required to just balance the weight of the proton and keep it moving horizontally? T

Explanation / Answer

As magnetic force = qvB sin = qvB (as = 90 degree)

Since weight of proton = mg

Hence

qvB = mg

B = mg /qv

B=(3.409583)(10)-14 T

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