A copper wire and a tungsten wire of the same length have the same resistance. What is the ratio of the diameter of the copper wire to that of the tungsten wire.

Therefore the ratio of diameter of the copper to that of the tungsten is

Explanation:

Resistance: Resistance is defined to the ratio of voltage to the electricity.

The resistance of a wire is

Therefore

ρ is the resistivity.

The unit of resistance is ohm (Ω).

The resistivity of copper(ρ₁) is 1.68×10⁻⁸ ohm-m

The resistivity of tungsten(ρ₂) is 5.6×10⁻⁸ ohm-m

For copper:

......(1)

Again for tungsten:

........(2)

Given that   and    

Dividing the equation (1) and (2)

  [since   and    ]

Therefore the ratio of diameter of the copper to that of the tungsten is

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the tires are rotating at 0.434 rpmlinear speed=45 m/sdiameter=0.550 mradius=0.275 mnow v= rωω= v/rω=45/0.275ω=163.6 rad/sω=163.6 rad/s (1rev/2π rad) (60s/1m)ω=1563 rpm