A metal rod of length 10 cm and a rectangular cross-section of 1 cm × 1 2 cm is connected to a battery across opposite faces. The resistance will be

Maximum when the battery is connected across 1 cm × 1 2 cm faces.

Maximum when the battery is connected across 10 cm × 1 cm faces.

Same irrespective of the three faces.

Maximum when the battery is connected across 10 cm × 1 2 cm faces.

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A wire of resistance $R$ and radius $r$ is stretched till its radius becomes $\frac{r}{2}$ . If now resistance of the stretched wire is $x R$ , then the value of $x$ is

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Important Questions on Current Electricity

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

An electric cable has just one copper wire of radius

8 mm

and resistance

10 Ω

. This single copper wire cable is replaced by

4

different well insulated copper wires each of radius

6 mm,

then total resistance of the cable is

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

A metal rod of length

10 cm

and a rectangular cross-section of

1 cm \times \frac{1}{2} cm

is connected to a battery across opposite faces. The resistance will be

EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

When operated at

240 V

, a current of

10 A

was seen flowing through a heating wire and it's temperature reaches to

1000 ° C

. If the temperature coefficient of the wire is

1 \times 10^{- 3} ° C^{- 1}

. Its resistance at a temperature of

0 ° C

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

A wire of

1 Ω

has a length of

1 m

. It is stretched till its length increases by

25 %

. The percentage change in resistance to the nearest integer is :

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

Space between two concentric conducting spheres of radii

a

and

b

(b > a)

is filled with a medium of resistivity

ρ

. The resistance between the two spheres will be:

EASY

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

Two copper wires, one of length

1 m

and the other of length

9 m

have the same resistance. The diameters are in the ratio

HARD

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

A tapered bar of length

L

and end diameters

D_{1}

and

D_{2}

is made of a material of electrical resistivity

ρ

. The electrical resistance of the bar is

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

What will be the length and diameter of a certain piece of copper, if it is to be shaped into a conductor of minimum resistance?

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

Masses of three wires of copper are in the ratio

1 : 3 : 5

and their lengths are in the ratio

5 : 3 : 1

. The ratio of their electrical resistance are

HARD

Physics>Electricity and Magnetism>Current Electricity>Electrical Resistance

Model a torch battery of length $l$ to be made up of a thin cylindrical bar of radius $a$ and a concentric thin cylindrical shell of radius $b$ filled in between with an electrolyte of resistivity $ρ$ (see figure). If the battery is connected to a resistance of value $R$ , the maximum Joule heating in $R$ will take place for :

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