Objective Questions Electrical Engineering

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1) Resistivity of a wire depends on
A. material

B. length

C. cross section area

D. all of above
 A  B  C  D
Resistivity is a basic property of any materials. It is defined as the resistance offered by a cube of unit volume of the materials. Hence resistivity of a wire depends on its material.

2) When n numbers resistances of each value r are connected in parallel, then the resultant resistance is x. When these n resistances are connected in series, total resistance is
A. nx.

B. n2x.

C. x/n.

D. rnx.
 A  B  C  D

n numbers resistances of each value r are connected in parallel, then the resultant resistance is x, that means r/n = x ⇒ r = nx.When these n resistances are connected in series, total resistance is nr = n.(nx) = n2x [Since r = nx alraedy proved]

3) Resistance of a wire is r ohms. The wire is stretched to double its length, then its resistance will be
A. r/2

B. 4r

C. 2r

D. r/4
 A  B  C  D

Resistance r = ρl/a. When the wire of length l is stretched to 2l, then the cross - sectional area of the wire becomes a/2. Now new value of resistance, r' = ρ2l/(a/2) = 4ρl/a = 4r.