A 60 W lightbulb has a resistance of 240 ohms. At the operating temperature of the tungsten filament, the resistivity is approximately5.0x10^-7 ohms. If the wire used to make the filament is 0.040 mm in diameter (a typical value), how long must the filament be

L = 6.032 m

Explanation:

The resistance of a wire is given by

      R = ρ L / A

done ρ is the resistivity of matter, L is the length and A is the area

      L = R A /ρ

the area of a circle is

    A = π r² = π d² / 4

    L = R π d² / 4ρ

in the problem they indicate the resistance of 240 Ω, the diameter of 0.040 mm and the resistivity of 5 10⁻⁷ Ω / m

Let's reduce the diameter to SI units

   d = 0.040 mm (1 m / 1000 mm) = 4 10⁻⁵ m

let's calculate

     L = 240 π (4 10⁻⁵) 2 / (4 5 10⁻⁷)

     L = 6.0319 m

     L = 6.032 m

where is the photo and the answer choices?

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

from wikipedia