A hank of uninsulated wire consisting of seven and a half turns is stretched between two nails hammered into a board to which the ends of the wire are fixed. The resistance of the circuit between the nails is determined with the help of electrical measuring instruments. Determine the proportion in which the resistance will change if the wire is unwound so that the ends remain to be fixed to the nails.
A.
225
B.
15
C.
240
D.
250
Answer :
225
Solution :
Let the resistance of half the turn be $$R.$$ Then in the former case, we have fifteen resistors of resistance $$R$$ connected in parallel, the total resistance being $$\frac{R}{{15}}.$$
In the latter case, we have the same fifteen resistors connected in series, the total resistance being $$15R.$$ Therefore, as a result of unwinding, the resistance of the wire will increase by a factor of 225.
Releted MCQ Question on Electrostatics and Magnetism >> Electric Current
Releted Question 1
The temperature coefficient of resistance of a wire is 0.00125 per $$^ \circ C$$ At $$300\,K,$$ its resistance is $$1\,ohm.$$ This resistance of the wire will be $$2\,ohm$$ at.
The electrostatic field due to a point charge depends on the distance $$r$$ as $$\frac{1}{{{r^2}}}.$$ Indicate which of the following quantities shows same dependence on $$r.$$
A.
Intensity of light from a point source.
B.
Electrostatic potential due to a point charge.
C.
Electrostatic potential at a distance r from the centre of a charged metallic sphere. Given $$r$$ < radius of the sphere.