Older televisions display a picture using a device called a cathode ray tube, where electrons are emitted at high speed and collide with a phosphorescent surface, causing light to be emitted. The paths of the electrons are altered by magnetic fields. Consider one such electron that is emitted with an initial velocity of 1.85 107 m/s in the horizontal direction when magnetic forces deflect the electron with a vertically upward acceleration of 5.45 1015 m/s2. The phosphorescent screen is a horizontal distance of 5.6 cm away from the point where the electron is emitted. (a) How much time does the electron take to travel from the emission point to the screen? (b) How far does the electron travel vertically before it hits the screen?

a)  t = 3.027 10⁻⁹ s ,  b)   y = 2.25 10⁻² m

Explanation:

We can solve this problem using the kinematic relations

a) as on the x-axis there is no relationship

          vₓ = x / t

          t = x / vₓ

We reduce the magnitudes to the SI system

          x = 5.6 cm (1m / 100 vm) = 0.056 m

we calculate

          t = 0.056 / 1.85 10⁷

          t = 3.027 10⁻⁹ s

b) the time is the same for the two movements, on the y axis

         y = v₀t + ½ a t²

as the beam leaves horizontal there is no initial vertical velocity

         y = ½ a t²

let's calculate

         y = ½  5.45 10¹⁵ (3.027 10⁻⁹)²

         y = 2.25 10⁻² m

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

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