A copper cable needs to carry a current of 160 A with a power loss of only 2.0 W/m. What is the required radius of the copper cable? (The resistivity of copper is 1.7 × 10 −8 Ω⋅m).

The radius of the cable is 0.0083 m or 8.3 mm.

Explanation:

The resistance of copper cable of 1 meter length will be given by

   ....     (i)

where the resistivity of copper is , and l is the length of the wire which is considered to be 1m, and a is the cross sectional area of the wire in .

From the formula of power we know that,    ....    (ii)

Therefore 2 W/m  =     ....     (iii)  

where  the resistance,R, actually means the resistance of the cable per meter.

Therefore R ( resistance of cable per meter)

= ohms / meter.       ....    (iv)

Therefore from (i)

=       .....     (v)

where cross sectional area of the cable, a  = ,

where r is the radius of the cable, and length of cable,l = 1m.

Therefore r  =

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.

the answer is a)

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