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.

MEDIUM

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Consider a resistor of uniform cross section area connected to a battery of internal resistance zero. The length of the resistor is doubled by stretching it then

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Important Questions on Current Electricity

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

Two solid conductors are made up of same material, have same length and same resistance. One of them has a circular cross section of area

A_{1}

and the other one has a square cross section of area

A_{2} .

The ratio

\frac{A_{1}}{A_{2}}

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

In a conductor, if the number of conduction electrons per unit volume is $8.5 \times 10^{28} m^{- 3}$ and mean free time is $25 f s$ (femtosecond), its approximate resistivity is: $(m_{e} = 9.1 \times 10^{- 31} k g)$

HARD

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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 :

Question Image

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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>Ohm's Law

The resistance of a wire is

R

ohm. If it is melted and stretched to

n

times its original length, its new resistance will be

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

A carbon resistor of

(56 \pm 5.6) kΩ

is to be marked with rings of different colours for its identification. The colour code sequence will be

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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

HARD

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

In an aluminum (Al) bar of square cross-section, a square hole is drilled and is filled with iron (Fe) as shown in the figure. The electrical resistivities of Al and Fe are

2.7 \times 10^{- 8} Ω m

and

1.0 \times 10^{- 7} Ω m

, respectively. The electrical resistance between the two faces P and Q of the composite bar is

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EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

A wire of resistance

12 ohms per meter

is bent to form a complete circle of radius

10 cm

. The resistance between its two diametrically opposite points,

A

and

B

as shown in the figure is

Question Image

HARD

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

Resistivity of the material of a conductor having uniform area of cross-section varies along its length on

x,

according to the relation

ρ = ρ_{0} (a + b x);

L

is length and

A

is cross-section area of conductor, then resistance of the conductor given by

(ρ_{0}, a, b

are constants)

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

Consider a cylindrical conductor of length

L

and area of cross-section

A

. The specific conductivity varies as

σ (x) = σ_{0} \frac{L}{\sqrt{x}}

where

x

is the distance along the axis of the cylinder from one of its ends. The resistance of the system along the cylindrical axis is

HARD

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

The electric resistance of a certain wire of iron is

R

. If its length and radius are both doubled, then

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

If the last band on the carbon resistor is absent, then the tolerance is

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

On stretching a wire its length is increased by

0.2 %

, its resistance will

MEDIUM

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

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>Ohm's Law

A uniform wire of length

l

and radius

r

has a resistance of

100 Ω

. It is recast into a wire of radius

\frac{r}{2}

. The resistance of new wire will be-

EASY

Physics>Electricity and Magnetism>Current Electricity>Ohm's Law

A wire made of aluminium having resistivity

ρ = 2.8 \times 10^{- 8} Ω - m

with a circular cross-section and has a radius of

2 \times 10^{- 3} m

. A current of

5 A

flows through the wire. If the voltage difference between the ends is

1 V

, the length of the wire in

m

Consider a resistor of uniform cross section area connected to a battery of internal resistance zero. The length of the resistor is doubled by stretching it then

Important Questions on Current Electricity

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