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A wire is stretched so as to change its diameter by $0.25 %$ . The percentage change in resistance is

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Important Questions on Current Electricity

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 17

Two wires of same dimensions but resistivities

ρ_{1}

and

ρ_{2}

are connected in series. The equivalent resistivity of the combination is

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 18

A resistance of

2 Ω

is to be made from a copper wire (specific resistance

= 1 .7 \times 10^{- 8} Ω m)

using a wire of length

50 cm

. The radius of the wire is

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 19

The specific resistance of a wire is

ρ

, its volume is

3 m^{3}

and its resistance is

3 Ω

, then its length will be

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 20

The

I - V

graphs for two different electrical appliances

P

and

Q

are shown in the diagram. If

R_{P}

and

R_{Q}

be the resistances of the devices, then

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 21

Consider a block of conducting material of resistivity

ρ

shown in the figure. Current $I$ enters at $A$ and leaves from $D$ . We apply the superposition principle to find voltage

Δ V

developed between $B$ and $C$ . The calculation is done in the following steps:
i) Take current

I

entering from

A

and assume it to spread over a hemispherical surface in the block.
ii) Calculate field

E (r)

at distance

r

from

A

by using ohm's law

E = ρ j

, where

r

is the current per unit area at

r

.
iii) From the

r

dependence of

E (r)

, obtain the potential

E (r)

r

.
iv) Repeat (i), (ii) and (iii) for current

I

leaving $D$ and superpose results for $A$ and $D$ .
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For current entering at

A

, the electric field at a distance

r

from $A$ is

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 22

Drift velocity,

v_{d}

, varies with the intensity of electric field as per the relation,

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 23

Drift speed of electrons, when

1.5 A

current flows in a copper wire of cross section

5 {mm}^{2}

v_{d} .

If the electron density in copper is

9 \times 10^{28} m^{- 3}

the value of

v_{d}

mm s^{- 1}

is close to (Take charge of an electron to be

= 1.6 \times 10^{- 19} C

)

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Achieve CUET (UG) Physics Practice Book>Chapter 3 - Current Electricity>Exercise>Q 24

A potential difference of

V

is applied at the ends of a copper wire of length

l

and diameter

d

. On doubling only

d

, the drift velocity,

A wire is stretched so as to change its diameter by 0.25%. The percentage change in resistance is

Important Questions on Current Electricity

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A wire is stretched so as to change its diameter by $0.25 %$ . The percentage change in resistance is