Question
In a cathode-ray tube (CRT), an electron travels ina vacuum and enters a region between two "deflection" plateswhich have equal and opposite charges. The dimension of eachplate are L=12 cm by d=3 cm, and the gap between them is h=2.5 mm (notto scale in the diagram). During a 0.001 s interval while it is between the plates, thechange of the momentum of the electron p is <0, 8.80 e-17, 0> kg m/s. What is the electric field between the plates? Hint: remember the Momentum Principle (the relationshipbetween Impulse and change in momentum.) What is the charge (both magnitude and sign) of the upperplate? q= _______________ C Please provide answers with the units specified. Thanks.
Explanation / Answer
change monmentum in y direction 8.8*10-17 =E*|e|*0.001s => E=550 kV/m in minus y direction =>E=<0,-550k,0> V/m the charges of the upper plate =q E=/0=q/(area*0) ; isconcentration of charges per m2 => q=1.75*10-8C, positive because E is pointing downward =>E=<0,-550k,0> V/m the charges of the upper plate =q E=/0=q/(area*0) ; isconcentration of charges per m2 => q=1.75*10-8C, positive because E is pointing downward