Current Electricity — DPP 3

20 NEET questions from Current Electricity, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

Attempt this test free 20 questions · 30 minutes · +80 marks
1
In meter bridge experiment, the value of unknown resistance is 2 Ω to get the balancing point 40 cm distance from the same end, then what will be the resistance in the resistance box?
  1. A 3 Ω
  2. B 6 Ω
  3. C 5 Ω
  4. D 12 Ω
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Correct answer: A

2
Two copper wires are of same length one of the wire is twice as thick as the other. Then the resistance of the two wires are in the ratio of
  1. A 1 : 16
  2. B 1 : 8
  3. C 1 : 4
  4. D 1 : 2
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Correct answer: C

3
Assertion (A): Potential measured by a voltmeter across a wire is always less than actual potential difference across it.
Reason (R): Finite resistance of voltmeter changes current flowing through the resistance across which potential difference is to be measured.
  1. A Both assertion and reason are true and reason is the correct explanation of assertion.
  2. B Both assertion and reason are true but reason is not the correct explanation of assertion.
  3. C Assertion is true but reason is false.
  4. D Assertion and reason both are false
Show answer

Correct answer: A

4
The opposition offered by the electrolyte of the cell to the flow of current through itself is known as
  1. A External resistance
  2. B Internal resistance
  3. C Non-resistance
  4. D Both (A) and (C)
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Correct answer: B

5
The charge on a capacitor decreases to η times in time t, when it discharges through a circuit with a time constant τ.
  1. A t = ητ
  2. B t = τ ln η
  3. C t = τ(ln η – 1)
  4. D $t=\tau \ln \left(1-\frac{1}{\eta}\right)$
Show answer & explanation

Correct answer: B

$\begin{array}{l}Q=Q_{0} e^{-t / \tau}=\mathrm{Q}_{0} / \eta \\ \text { or } \mathrm{e}^{-\mathrm{t} / \tau}=\frac{1}{\eta} \\ \text { or } \mathrm{e}^{\mathrm{t} / \tau}=\eta \\ \text { or } \frac{\mathrm{t}}{\tau}=\ln \eta\end{array}$
Therefore, option (B) is the correct answer.
6
The length of given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter, the change in the resistance of the wire will be
  1. A 200%
  2. B 100%
  3. C 50%
  4. D 300%
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Correct answer: D

7
Eels are able to generate current with biological cells called electro-plaque. The electro-plaque’s in an eel are arranged in 100 rows, each row stretching horizontally along the body of the fish containing 5000 electro-plaques. The arrangement is suggestively shown below. Each electro-plaque has an emf of 0.15 V and internal resistance of 0.25 Ω. The water surrounding the eel completes a circuit between the head and its tail. If the water surrounding it has a resistance of 500 Ω. The current an eel can produced in water is about
Current Electricity – NEET-10175
  1. A 1.5 A
  2. B 3.0 A
  3. C 15 A
  4. D 30 A
Show answer & explanation

Correct answer: A

In each row, all the 5000 electroplaque are connected in series.
Net emf for each row 0.15 × 5000 = 750 V
Net resistance of each row 0.25 × 5000 = 1250 Ω
Now all 100 rows are connected in parallel.
Net emf for the network = 750 V.
Equivalent resistance of 100 rows = $\frac{1250}{100}$ = 12.50 Ω
External resistance = 500 Ω, Current through 500 Ω, resistance,
$I=\frac{E}{R+r}=\frac{750}{500+12.5}=1.46 \mathrm{~A} \approx 1.5 \mathrm{~A}$
Therefore, option (A) is the correct answer.
8
A current of 4.8 A is flowing in a conductor. The number of electrons passing through any cross-section per second is
  1. A $3 \times 10 ^ { 19 }$
  2. B $76.8 \times 10 ^ { 20 }$
  3. C $7.68 \times 10 ^ { 12 }$
  4. D $3 \times 10 ^ { 10 }$
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Correct answer: A

9
Two electric bulbs, each designed to operate with a power of 500W in 220V line, are connected in series in a 110V line. The power generated by each bulb will be
  1. A 11 W
  2. B 312.5 W
  3. C 22 W
  4. D 31.25 W
Show answer & explanation

Correct answer: D

Resistance $R=\frac{V^{2}}{P}$
$\therefore \quad$ Total power $=\frac{V^{\prime 2}}{2 R}=\frac{V^{\prime 2} P}{2 V^{2}}=\frac{500 \times 110 \times 110}{2 \times 220 \times 220}=62.5 \mathrm{~W}$
Power in a single bulb = 31.25W
Therefore, option (D) is the correct answer.
10
The charge flowing through a resistance R varies with time t as Q = at – bt$^{2}$. The total heat produced in R is
  1. A $\frac{a^{3} R}{6 b}$
  2. B $\frac{a^{3} R}{3 b}$
  3. C $\frac{a^{3} R}{2 b}$
  4. D $\frac{a^{3} R}{b}$
Show answer & explanation

Correct answer: A

Current Electricity – NEET-10147 Therefore, option (A) is the correct answer.
11
Two bulbs of 40W and 60W and of rated voltage 240V are connected in series across a potential difference of 420V. Which bulb will work at above its rated voltage?
  1. A 40 W bulb
  2. B 60 W bulb
  3. C Both will work
  4. D Data is insufficient to suggest
Show answer & explanation

Correct answer: B

Resistance of 40 W bulb = $\frac{240 \times 240}{40}$ = 1440 Ω
Its safe current = $\frac{240}{1440}$ = 0.167 A
Resistance of 60W bulb = $\frac{240 \times 240}{60}$ = 960 Ω
Its safe current = $\frac{240}{960}$ = 0.25 A
R$_{eq}$ = R$_{1}$ + R$_{2}$ = 2400 Ω
$\therefore \quad I=V / R_{\text {eq. }}=420 / 2400=0.2 \mathrm{~A}$
Therefore, option (B) is the correct answer.
12
Five resistances are combined according to the figure. The equivalent resistance between the point X and Y will be
Current Electricity – NEET-10189
  1. A 10 Ω
  2. B 22 Ω
  3. C 20 Ω
  4. D 50 Ω
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Correct answer: A

13
The rate of flow of electric charges through any cross-section of a conductor is known as
  1. A Electric flux
  2. B Electric potential
  3. C Electric current
  4. D Electric field
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Correct answer: C

14
Three copper wires of length and cross-sectional area (L, A), (2L, A/2), and (L/2, 2A). Resistance is minimum in
  1. A Wire of cross-sectional area A
  2. B Wire of area A/2
  3. C Wire of cross-sectional area 2A
  4. D Same in all three cases
Show answer

Correct answer: C

15
The reciprocal of resistivity is called
  1. A Resistance
  2. B Electric current
  3. C Conductivity
  4. D Conductance
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Correct answer: C

16
A and B are two points on a uniform ring of resistance 15 Ω. The ∠AOB = 45°. The equivalent resistance between A and B is:
  1. A 1.64 Ω
  2. B 2.84 Ω
  3. C 4.57 Ω
  4. D 2.64 Ω
Show answer & explanation

Correct answer: A

Resistance of part ADB, $R_{1}=15 \times \frac{45}{360}=1.875 \Omega$
Resistance of part ACB, R$_{2}$ = 15 – 1.875 = 13.125 Ω
Current Electricity – NEET-10127 $\begin{array}{l}R_{A B}=\frac{13.125 \times 1.875}{13.125+1.875} \\ R_{A B}=1.64 \Omega\end{array}$
Therefore, option (A) is the correct answer.
17
Specific resistance of a wire depends on its
  1. A Mass
  2. B Length
  3. C Area of cross-section
  4. D Material property
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Correct answer: D

18
A heater coil is cut into two equal parts and only one part is used in the heater. The heat generated now, as compared to that when full coil was used, will be (Assuming potential is same in both cases);
  1. A one fourth
  2. B halved
  3. C doubled
  4. D four times
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Correct answer: C

19
A galvanometer of resistance 100 Ω gives full-scale deflection for 10 mA current. What should be the value of shunt so that it can measure a current of 100 mA?
  1. A 11.11 Ω
  2. B 9.9 Ω
  3. C 1.1 Ω
  4. D 4.4 Ω
Show answer & explanation

Correct answer: A

$\mathrm{S}=\frac{\mathrm{gI}_{\mathrm{g}}}{\mathrm{I}-\mathrm{I}_{\mathrm{g}}}=\frac{100}{9}=11.11 \Omega$
Therefore, option (A) is the correct answer.
20
Which of the following is non-ohmic resistance?
  1. A Lamp filament
  2. B Copper wire
  3. C Carbon resistor
  4. D Diode
Show answer

Correct answer: D

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