Consider a wire that has resistance r, length l and the cross-sectional area a. the correct expression for the resistivity of that wire is:

Explanation:

.As we know that the resistance of the wire is given as

here we know that

A = cross-sectional area

L = length

R = resistance of wire

now multiply both sides of above equation with Area

now divide both sides with length of the wire

so above is the expression of resistivity of wire in terms of resistance, Area and length of the wire

this could be newton#'s law of cooling. the cooling curve is exponential

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