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# 31 Years NEET Previous Year Questions: Current Electricity - 3

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## 30 Questions MCQ Test Physics Class 12 | 31 Years NEET Previous Year Questions: Current Electricity - 3

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31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 1

### The masses of the three wires of copper are inthe ratio of 1 : 3 : 5 and their lengths are in theratio of 5 : 3 : 1. The ratio of their electricalresistance is [1988]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 1

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 2

### Two batteries of emf 4 V and 8V with internal resistance 1 Ω and 2 Ω are connected in a circuit with a resistance of 9 Ω as shown in figure. The current and potential difference between the points P and Q are [1988]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 2

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 3

### n equal resistors are first connected in seriesand then connected in parallel. What is the ratioof the maximum to the minimum resistance ?[1989]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 3

In series, Rs= nR

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 4

Forty electric bulbs are connected in series across a 220 V supply. After one bulb is fused the remaining 39 are connected again in series across the same supply. The illumination will be     [1989]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 4

Since, the voltage is same for the two
combinations, therefore

H ∝ 1/R.

Hence, the
combination of 39 bulbs will glow more.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 5

A current of 2 A, passing through a conductorproduces 80 J of heat in 10 seconds. Theresistance of the conductor in ohm is [1989]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 5

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 6

Two identical batteries each of e.m.f 2V andinternal resistance 1Ω are available to produceheat in an external resistance by passing a currentthrough it. The maximum power that can bedeveloped across R using these batteries is   [1990]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 6

For maximum current, the two batteries
should be connected in series. The current
will be maximum when external resistance is
equal to the total internal resistance of cells
i.e. 2Ω. Hence power devloped across the
resistacne R will be

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 7

You are given several identical resistances eachof value R = 10Ω and each capable of carrying amaximum current of one ampere. It is required tomake a suitable combination of these resistancesof 5Ω which can carry a current of 4 ampere. Theminimum number of resistances of the type Rthat will be required for this job is [1990]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 7

To carry a current of 4 ampere, we need four
paths, each carrying a current of one ampere.

Let r be the resistance of each path. These
are connected in parallel. Hence, their
equivalent resistance will be r/4. According
to the given problem r/4 = 5 or r = 20Ω
For this propose two resistances should be
connected. There are four such
combinations. Hence, the total number of
resistance = 4 × 2 = 8.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 8

In the network shown in the Fig, each resistance is 1Ω. The effective resistance between A and B  is   [1990]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 8

At A current is distributed and at B currents
are collected. Between A and B, the
distribution is symmetrical. It has been
shown in the figure. It appears that current
in AO and OB remains same. At O, current i4
returns back without any change. If we
detach O from AB there will not be any
change in distribution.
Now, CO & OD will be in series hence its
total resistance = 2Ω
It is in parallel with CD, so, equivalent
resistance =

This equivalent resistance is in series with
AC & DB, so, total resistance

Now 8/3 Ω is parallel to AB, that is, 2Ω so
total resistance

Between C & D, the equivalent resistance is
given by

Equivalent resistance along

∴ Effective resistance between A and B is

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 9

Faraday’s laws are consequence of conservationof [1991]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 9

Faraday’s laws are based on the conversion
of electrical energy into mechanical energy;
which is in accordance with the law of
conservation of energy

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 10

The velocity of charge carriers of current (about1 amp) in a metal under normal conditions is ofthe order of [1991]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 10 The velocity of charge carriers of current 1 ampere in ametal under normal conditions is of the order of a fraction ofmm/sec
31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 11

Direct current is passed through a coppersulphate solution using platinum electrodes. Theelements liberated at the electrodes are [1993]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 11

In the electrolysis of CuSO4, oxygen is
liberated at anode and copper is deposited
at cathode.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 12

Three resistances each of 4 Ω are connected toform a triangle. The resistance between any twoterminals is [1993]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 12

The two resistances are connected in series
and the resultant is connected in parallel with
the third resistance.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 13

Current through 3 Ω resistor is

0.8 amp., then potential drop through 4Ω resistor is           [1993]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 13

Voltage across 3 Ω resistance = 3 × 0.8 = 2.4V
This voltage is the same across 6 Ω
resistance. Hence current through this
resistance

Total current in the circuit
= 0.8 + 0.4 = 1.2 amp
Voltage across 4 Ω resistance
= 4 × 1.2 = 4.8 volts

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 14

A 4 μF capacitor is charged to 400 volts andthen its plates are joined through a resistance of1k Ω. The heat produced in the resistance is           [1994]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 14

The energy stored in the capacitor

This energy will be converted into heat in
the resistor.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 15

In the circuit shown in Fig, the current in 4 Ω resistance is 1.2 A. What is the potential difference between B and C.       [1994]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 15

The potential difference across 4Ω resistance
is given by

V = 4 × i1 = 4 × 1.2 = 4.8 volt

So, the potential across 8Ω resistance is also
4.8 volt.

Current in 2Ω resistance i = i1 + i2
∴ i = 1.2 + 0.6 = 1.8 amp
Potential difference across 2Ω resistance
VBC = 1.8 × 2 = 3.6volts

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 16

A heating coil is labelled 100 W, 220 V. The coil iscut in half and the two pieces are joined in parallelto the same source. The energy now liberatedper second is [1995]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 16

Power of heating coil = 100 W and voltage
(V) = 220 volts. When the heating coil is cut
into two equal parts and these parts are
joined in parallel, then the resistance of the
coil is reduced to one-fourth of the previous
value. Therefore energy liberated per second
becomes 4 times i.e., 4 × 100 = 400 J.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 17

If a wire of resistance R is melted and recasted tohalf of its length, then the new resistance of thewire will be [1995]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 17

Initial resistance (R1) = R; Initial length is
1and final length ( 2) = 0.5 . Volume of a
wire = . A. Since the volume of the wire
remains the same after recasting, therefore

We also know that resistance of a wire (R)

[Alt : When wires are drawn from same
volume but with different area of
cross-section, then

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 18

Two wires of the same metal have same length,but their cross-sections are in the ratio 3:1. Theyare joined in series. The resistance of thickerwire is 10Ω. The total resistance of thecombination will be [1995]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 18

Length of each wire = ; Area of thick wire
(A1) = 3A; Area of thin wire (A2) = A and resistance of thick wire (R1) = 10 Ω

Resistance   (if is constant)

The equivalent resistance of these two
resistors in series
= R1 + R, = 30 + 10 = 40Ω.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 19

If the resistance of a conductor is 5 Ω at 50ºCand 7Ω at 100ºC, then the mean temperature coefficient of resistance (of the material) is[1996]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 19

Explanation : We know that RT = R0(1+αT)  where RT = resistance at temp T, R0 = resistance at temp T = 0oC and α= temperature coefficient of resistance.

Here, 5 = R0(1+α.50)...(1)

and 7 = R0(1+α.100)...(2)

(2)/(1)

⇒ 7/5 = (1+100α)/(1+50α)

7+350α = 5+500α

150α=2

⇒α=2/150

=0.013/oC

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 20

What will be the equivalent resistance of circuitshown in figure between two points A and D   [1996]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 20

Equivalent Circuit

Equivalent Resistance of circuit

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 21

If a negligibly small current is passed through awire of length 15 m and of resistance 5Ω havinguniform cross-section of 6 × 10–7 m2 , thencoefficient of resistivity of material, is [1996]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 21

Given : Length of wire (l) = 15m
Area (A) = 6 × 10–7 m2
Resistance (R) = 5Ω.
We know that resistance of the wire material

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 22

Kirchoff’s first law, i.e. ∑i = 0 at a junction, dealswith the conservation of [1992, 1997]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 22

We know from the Kirchhoff 's first law that
the algebraic sum of the current meeting at
any junction in the circuit is zero (i.e. ∑i = 0)
or the total charge remains constant.
Therefore, Kirchhoff's first law at a junction
deals with the conservation of charge

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 23

A (100 W, 200 V) bulb is connected to a 160Vpower supply. The power consumption would be    [1997]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 23

Power = 100 W, Voltage = 200 V

Resistance of bulb =

When bulb is applied across 160 V,
Current in bulb = 160/400 A

Power consumption =

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 24

There are three copper wires of length and cross sectional area .   Inwhich case is the resistance minimum?   [1997]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 24

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 25

The current in the following circuit is           [1997]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 25

Resistance of ACB, R' = 3Ω + 3Ω = 6Ω.
For net resistance between A and B; R' = 6Ω
and 3Ω are in parallel.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 26

Three equal resistors connected across a sourceof e.m.f. together dissipate 10 watt of power.What will be the power dissipated in watts if thesame resistors are connected in parallel acrossthe same source of e.m.f.?      [1998]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 26

In series, Equivalent resistance = 3R

∴ Equivalent resistance R' = R/3

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 27

If nearly 105 coulombs liberate 1 gm-equivalentof aluminium, then the amount of aluminium(equivalent weight 9), deposited throughelectrolysis in 20 minutes by a current of 50 amp.will be [1998]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 27

m = Zit, 9 = Z × 105, Z= 9 × 10–5
Again,
m = Zit = 9 × 10–5 × 50 × 20 × 60 = 5.4 gm

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 28

A 5ºC rise in temperature is observed in aconductor by passing a current. When thecurrent is doubled the rise in temperature will beapproximately [1998]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 28

Since H ∝ I2 , doubling the current will
produce 4 times heat. Hence, the rise in
temperature will also be 4 times i.e., rise in
temperature = 4 × 5 = 20ºC.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 29

The resistance of a discharge tube is [1999]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 29

In discharge tube the current is due to flow
of positive ions and electrons. Moreover,
secondary emission of electrons is also
possible. So V-I curve is non-linear; hence
resistance is non-ohmic.

31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 30

The current (I) in the given circuit is [1999]

Detailed Solution for 31 Years NEET Previous Year Questions: Current Electricity - 3 - Question 30

In circuit, RB and RC are in series, so, Rs = 6 +
6 = 12Ω. This 12 Ω resistance is in parallel
with RA = 3 Ω,
So, equivalent resistance of circuit

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