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Current Electricity Set-4 MCQ Online Practice Test | Class 12 | Quiz Tweek

Current Electricity Set-4

Practice Important MCQs for Current Electricity — Physics, Class 12.

Current Electricity is a core CBSE Class 12 Physics chapter because it builds the fundamental ideas behind resistances in series/parallel, internal resistance of cells, power delivery, and the working of potentiometer-based measurements. These concepts are frequently asked in both board exams and competitive tests (JEE/NEET) due to their direct link with circuit analysis, graph/inequality reasoning, and efficiency/power optimization problems.

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Q1. A uniform metallic wire of initial length $L$ has resistance $R$ . It is stretched uniformly to a new length $2L$ while its volume remains constant. What is the new resistance of the wire?

(A)

Option A $2R$

(B)

Option B $\dfrac{R}{2}$

(C)

Option C $4R$

(D)

Option D $R$

Q2. Two cylindrical wires A and B of equal length $L$ are made from the same material. The radius of B is twice that of A ( $r_B=2r_A$ ). They are first connected in parallel across a battery of emf $V$ (internal resistance negligible) and the power dissipated in wire A is $P_p$ . Then the same wires are connected in series across the same battery and the power dissipated in wire A is $P_s$ . What is the ratio $\dfrac{P_p}{P_s}$ ?

(A)

Option A $\dfrac{25}{16}$

(B)

Option B $\dfrac{5}{4}$

(C)

Option C $\dfrac{16}{25}$

(D)

Option D $4$

Q3. A cylindrical conductor of length $L$ has radius varying linearly from $r_0$ at $x=0$ to $2r_0$ at $x=L$ . The resistivity is $\rho$ (constant). What is the resistance between the two ends of the conductor?

(A)

Option A $\dfrac{\rho L}{\pi r_0^{2}}$

(B)

Option B $\dfrac{2\rho L}{\pi r_0^{2}}$

(C)

Option C $\dfrac{\rho L}{4\pi r_0^{2}}$

(D)

Option D $\dfrac{\rho L}{2\pi r_0^{2}}$

Q4. A battery of emf $12\ \mathrm{V}$ and internal resistance $1\ \Omega$ is connected in series with a resistor $R_1=5\ \Omega$ . After $R_1$ the circuit splits into two branches: Branch 1 has $R_2=10\ \Omega$ in series with an ammeter of internal resistance $1\ \Omega$ ; Branch 2 has $R_3=20\ \Omega$ . The branches rejoin and return to the battery. What current does the ammeter read (magnitude)?

(A)

Option A $0.372\ \mathrm{A}$

(B)

Option B $0.592\ \mathrm{A}$

(C)

Option C $0.916\ \mathrm{A}$

(D)

Option D $1.250\ \mathrm{A}$

Q5. A cell of emf $e=1.50\ \mathrm{V}$ is balanced on a potentiometer at length $l_1=60\ \mathrm{cm}$ when it is open-circuited. When a resistor $R=10\ \Omega$ is connected across the cell, the new balance length becomes $l_2=48\ \mathrm{cm}$ . Assuming the potentiometer driver and wire remain unchanged, the internal resistance $r$ of the cell is:

(A)

Option A $1.5\ \Omega$

(B)

Option B $1.0\ \Omega$

(C)

Option C $2.5\ \Omega$

(D)

Option D $5.0\ \Omega$

Q6. A uniform wire of length $L$ , cross-sectional area $A$ , and resistivity $\rho$ has resistance $R$ . The wire is stretched uniformly to length $2L$ without changing its volume. What is the new resistance?

(A)

$\dfrac{R}{2}$

(B)

$2R$

(C)

$4R$

(D)

$\dfrac{R}{4}$

Q7. A wire of length $L$ and resistivity $\rho$ has cross-sectional area varying along its length as $A(x)=A_0\!\left(1+\beta\frac{x}{L}\right)$ for $0\le x\le L$ . The resistance of the wire between its ends is

(A)

$\displaystyle \frac{\rho L}{A_0\beta}\ln(1+\beta)$

(B)

$\displaystyle \frac{\rho L}{A_0}\ln(1+\beta)$

(C)

$\displaystyle \frac{\rho L}{A_0(1+\beta)}$

(D)

$\displaystyle \frac{\rho L}{A_0}\!\left(1+\frac{\beta}{2}\right)$

Q8. A battery of emf $E$ and internal resistance $r$ supplies a current $I_1$ to an external resistor $R$ . When an identical resistor $R$ is connected in parallel with the first resistor, the current drawn from the battery becomes $1.5I_1$ . What is the ratio $r/R$ ?

(A)

$1$

(B)

$\dfrac{1}{3}$

(C)

$2$

(D)

$\dfrac{1}{2}$

Q9. Two identical cells, each of emf $E$ and internal resistance $r$ , supply power to an external resistor $R$ in two configurations: (i) the cells in series across $R$ , (ii) the cells in parallel across $R$ . For which condition on $R$ and $r$ does configuration (i) deliver more power to $R$ than (ii)?

(A)

For $R<r$

(B)

For $R>r$

(C)

For $R=r$

(D)

Always (independent of $R$ and $r$ )

Q10. Two cells with emfs $E_1$ and $E_2$ and internal resistances $r_1$ and $r_2$ , respectively, are connected in parallel (positive to positive, negative to negative) with no external load. Assuming $E_1>E_2$ , the steady current that flows from the higher-emf cell into the lower-emf cell has magnitude

(A)

$\displaystyle \frac{E_1-E_2}{r_1+r_2}$

(B)

$\displaystyle \frac{E_1-E_2}{|r_1-r_2|}$

(C)

$\displaystyle \frac{E_1+E_2}{r_1+r_2}$

(D)

$\displaystyle \frac{E_1-E_2}{r_1r_2}$

Q11. A uniform metallic wire of length $L$ , cross-sectional area $A$ and resistance $R$ is stretched to a new length $2L$ while its volume remains constant. What is the new resistance of the wire?

(A)

Option A $2R$

(B)

Option B $\dfrac{R}{2}$

(C)

Option C $4R$

(D)

Option D $8R$

Q12. A battery of emf $E=12\ \text{V}$ and internal resistance $r$ is connected to resistors $R_1=4\ \Omega$ and $R_2=6\ \Omega$ in series. The potential difference across $R_2$ is measured to be $6\ \text{V}$ . The value of $r$ is:

(A)

Option A $1\ \Omega$

(B)

Option B $2\ \Omega$

(C)

Option C $3\ \Omega$

(D)

Option D $4\ \Omega$

Q13. Two cells — one of emf $12\ \text{V}$ with internal resistance $1\ \Omega$ , the other of emf $6\ \text{V}$ with internal resistance $2\ \Omega$ — are connected in parallel and supply an external resistor $R=10\ \Omega$ . The current through the external resistor is:

(A)

Option A $0.83\ \text{A}$

(B)

Option B $0.90\ \text{A}$

(C)

Option C $1.125\ \text{A}$

(D)

Option D $\dfrac{15}{16}\ \text{A}$

Q14. Two identical cells each of emf $E$ and internal resistance $r$ are used to supply a variable external resistor $R$ . For which range of $R$ does the series connection of the two cells deliver greater power to $R$ than the parallel connection?

(A)

Option A $R>r$

(B)

Option B $R<r$

(C)

Option C $R=r$

(D)

Option D Power is the same for all $R$

Q15. A resistor $R$ and an initially uncharged capacitor $C$ are connected in series with a battery of emf $E$ at $t=0$ . The switch is closed at $t=0$ . The instantaneous power delivered to the capacitor is $P_C(t)=i(t)\,v_C(t)$ . At what time after closing the switch is $P_C(t)$ maximum?

(A)

Option A $t=0$

(B)

Option B $t=RC\ln 2$

(C)

Option C $t=RC$

(D)

Option D $t=\dfrac{RC}{2}\ln 2$

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