Question

Early black-and-white television sets used an electron beam to draw a picture on the screen. The electrons in the beam were accelerated by a voltage of 3.0 kV; the beam was then steered to different points on the screen by coils of wire that produced a magnetic field of up to 0.66 T .

A.

What is the speed of electrons in the beam?

Express your answer with the appropriate units. v= __________

B.

What acceleration do they experience due to the magnetic field, assuming that it is perpendicular to their path? What is this acceleration in units of g? a=__________ g

C.

If the electrons were to complete a full circular orbit, what would be the radius?

Express your answer with the appropriate units. r=_________

Answer 1

A) Speed of electrons in the beam: AKE = AVq KE, - KE, = AVI -m0,2 – 0 = AVO Vo =/2009 2(3x103 V)(1.6x10-19 C) (9.11x10-31 kg) = 3.24x10² m/s B) Using the eq: F=qvB sino = (1.6x10-1° C)(3.24 x 10² m/s)(0.66 T)sin 90° = 3.42 x 10-12 N For acceleration using the eq: F = ma a= m 3.42 x10-12 N 9.11x10-31 kg 3.75x1018 m/s2 9.8 m/s? = 3.83 x 1017 g For radius using the eq: (3.24x10² m/s)? 3.75x1018 m/s? = 2.79x104 m