Current Electricity

35 solved questions from Class 12 Physics, each with the full working. Tap any question to see the step-by-step solution.

• 1 What is the fundamental law or governing principle of 'Current Electricity' in Class 12 Physics? medium MCQ Fundamental Physical Law
• 2 What is the SI unit and dimensional formula for the key physical quantity studied in 'Current Electricity'? medium MCQ SI Units & Dimensional Analysis
• 3 How does the field or potential intensity vary with distance r in 'Current Electricity'? medium MCQ Spatial Distance Dependence
• 4 What is the net flux or circulation integral through a closed surface in 'Current Electricity'? medium MCQ Gauss's Theorem & Boundary Integrals
• 5 Why do field lines in 'Current Electricity' never intersect each other? medium MCQ Field Line Properties
• 6 What is the SI unit of electrical resistance? easy 1 mark SI units of electrical quantities
• 7 An ideal battery of emf 12 V and internal resistance 0.5 Ω supplies current to two resistors R_1=4,Omega and R_2=6,Omega connected in parallel. Calculate (i) the current through each resistor, (ii) the total power delivered by the battery. Then a switch is closed connecting R_2 in series with a third resistor R_3=3,Omega (parallel with R_1). Find the new current from the battery and the new total power dissipated. hard 5 marks Kirchhoff’s circuit laws
• 8 A copper wire of length 2.0,m and cross‑sectional area 1.5,mm^2 has resistivity 1.68×10^-8,Ω-m at 20°C. What is its resistance? medium MCQ 2 marks Ohm’s law and resistivity
• 9 The resistance of a metal rod at 20°C is 5.0,Ω. Its temperature coefficient of resistance is 0.004,per;°C. What is its resistance at 80°C? medium 2 marks Temperature dependence of resistance
• 10 A copper conductor of length 2 m and cross‑sectional area 2 mm^2 carries a current of 5 A. The number density of free electrons in copper is n = 8.5×10^28 m^-3. (i) Find the drift speed of the electrons. (ii) Explain why the drift speed is so small compared to the speed of an electric signal in the wire. hard 5 marks Drift velocity of electrons in a conductor
• 11 In a Wheatstone bridge, three known resistances are R_1 = 10 Ω, R_2 = 20 Ω, and R_3 = 30 Ω. The bridge is balanced when the galvanometer shows zero current. Find the value of the unknown resistance R_x placed opposite R_3. hard 3 marks Balanced Wheatstone bridge condition
• 12 A nichrome wire of length 1.5 m and cross‑sectional area 0.8 mm^2 has a resistivity of 1.10×10^-6 Ω m at 20°C. What is its resistance? easy MCQ 1 mark Resistance from resistivity
• 13 A 9 V ideal battery has an internal resistance of 0.2 Ω. It is connected to a lamp whose resistance is 3 Ω. (i) Find the terminal voltage across the lamp. (ii) Find the power dissipated in the lamp. medium 2 marks Terminal voltage and power with internal resistance
• 14 In a Wheatstone bridge, three resistances are R_1=12,Omega, R_2=8,Omega and R_3=18,Omega. The bridge is balanced when a galvanometer shows zero current. (i) Find the value of the unknown resistance R_x connected across the arm opposite R_3. (ii) If R_2 is increased by 20% while R_1 and R_3 remain unchanged, what must R_x be changed to so that the bridge remains balanced? hard 3 marks Wheatstone bridge balance condition
• 15 A 12 V ideal battery has an internal resistance of 0.3 Ω and powers a lamp of resistance 5 Ω. (i) What is the terminal voltage across the lamp? (ii) What is the power dissipated in the lamp? medium 2 marks Battery internal resistance and power dissipation
• 16 A nichrome wire has length 1.8,m, cross‑sectional area 0.6,mm^2 and resistivity 1.10×10^-6,Ω,m at 20°C. Calculate its resistance. easy 1 mark Resistivity and resistance calculation
• 17 Which of the following equations correctly represents the power dissipated in a resistor of resistance R through which a current I flows? easy MCQ 1 mark Power dissipation in resistors
• 18 A copper wire has length L = 3.5 m and cross‑sectional area A = 0.9 mm^2. The resistivity of copper at 20°C is ρ = 1.68×10^-8 Ω m. Calculate the resistance of the wire. easy 1 mark Resistance from resistivity
• 19 A circuit consists of a 12 V ideal battery with internal resistance r=0.2 Ω connected to two resistors R_1=4 Ω and R_2=6 Ω which are in parallel. The combination is then connected in series with a resistor R_3=8 Ω. Using Kirchhoff's laws, find (i) the current supplied by the battery, (ii) the current through each resistor R_1,R_2,R_3, and (iii) the total power delivered by the battery. hard 5 marks Kirchhoff's laws in combined circuits
• 20 An ideal battery of emf E=15 V has an internal resistance r=0.5 Ω. It is connected to a load resistor R=10 Ω. (i) Find the terminal voltage across the load. (ii) Find the power dissipated in the load. medium 2 marks Internal resistance effect
• 21 An 18,V ideal battery with internal resistance r=0.4,Ω is connected to two resistors R_1=5,Ω and R_2=15,Ω in parallel. The combination is then connected in series with a resistor R_3=10,Ω. (i) Find the total resistance seen by the battery. (ii) Find the current supplied by the battery. (iii) Find the power dissipated in R_3. medium 3 marks Series‑parallel circuits and power
• 22 A metal wire of length L=3.0,m and cross‑sectional area A=0.5,mm^2 carries a current I=4.0,A. The number density of free electrons is n=9×10^28,m^-3. (i) Find the drift speed of the electrons. (ii) Explain why the drift speed is so small compared to the speed of an electric signal in the wire. hard 4 marks Electron drift speed
• 23 In a Wheatstone bridge, the known resistances are R_1=16,Omega, R_2=12,Omega, R_3=24,Omega and an unknown resistor R_4 is connected opposite R_3. (i) Find the value of R_4 that balances the bridge. (ii) If R_2 is increased by 25 % while R_1 and R_3 remain unchanged, what must R_4 be changed to so that the bridge remains balanced? hard 4 marks Wheatstone bridge balance
• 24 In a Wheatstone bridge, R_1 = 15 Ω, R_2 = 10 Ω, R_3 = 30 Ω and the unknown resistor R_x is connected opposite R_3. (i) Find the value of R_x that balances the bridge. (ii) If R_2 is increased by 15% while R_1 and R_3 remain unchanged, what must the new value of R_x be to keep the bridge balanced? hard 3 marks Balancing condition of Wheatstone bridge
• 25 A circuit consists of a 9 V ideal battery with internal resistance r = 0.5 Ω. It is connected to three resistors as follows: R_1 = 2 Ω and R_2 = 4 Ω are in parallel; this parallel combination is in series with R_3 = 6 Ω. (i) Using Kirchhoff's laws, find the current supplied by the battery. (ii) Determine the current through each resistor R_1, R_2, and R_3. (iii) Find the total power delivered by the battery. hard 4 marks Kirchhoff's laws and current division
• 26 A copper wire has length L = 4.2 m and cross‑sectional area A = 1.2 mm^2. The resistivity of copper at 20°C is ρ = 1.68×10^-8 Ω m. Calculate the resistance of the wire. easy 1 mark Resistance of a uniform conductor
• 27 A copper wire has length L = 5.0,m and cross‑sectional area A = 1.0,mm^2. The resistivity of copper at 20°C is ρ = 1.68×10^-8,Ωm. Calculate the resistance of the wire. easy 1 mark Resistivity of a wire
• 28 A copper wire of length L=4.0,m, cross‑sectional area A=0.8,mm^2, and free‑electron number density n=8.5×10^28,m^-3 carries a current I=5.0,A. (i) Find the drift speed of the electrons. (ii) Explain why the drift speed is so small compared to the speed of an electric signal in the wire. hard 5 marks Electron drift velocity in conductors
• 29 A 12,V ideal battery with internal resistance r=0.30,Ω is connected to two resistors R_1=3,Ω and R_2=6,Ω in parallel. This parallel combination is then connected in series with a resistor R_3=9,Ω. Using Kirchhoff’s laws, find (i) the total current supplied by the battery and (ii) the current through each resistor R_1, R_2, and R_3. medium 3 marks Kirchhoff’s laws in a mixed circuit
• 30 A metal wire has length L=3.0 m and cross‑sectional area A=0.6 mm^2. The free‑electron number density is n=9×10^28,m^-3 and the wire carries a current I=6,A. (i) Find the drift speed of the electrons. (ii) Explain why the drift speed is so small compared to the speed of an electric signal in the wire. hard 5 marks Drift speed of electrons in a conductor
• 31 In a Wheatstone bridge, the resistances are R_1=12,Omega, R_2=8,Omega, R_3=18,Omega, and an unknown resistor R_x is connected opposite R_3. (i) Find the value of R_x that balances the bridge. (ii) If R_2 is increased by 20% while R_1 and R_3 remain unchanged, what must R_x be changed to keep the bridge balanced? hard 4 marks Wheatstone bridge balance condition
• 32 A 10 V ideal battery with internal resistance r=0.4,Ω is connected to a circuit where resistors R_1=3,Ω and R_2=5,Ω are in series. The series combination is then connected in parallel with a resistor R_3=2,Ω. Using Kirchhoff’s laws, find (i) the total current supplied by the battery, (ii) the current through each resistor R_1, R_2, and R_3. medium 3 marks Kirchhoff’s laws and series–parallel circuits
• 33 A copper wire has length L=7.5 m and cross‑sectional area A=2.0 mm^2. The resistivity of copper at 20°C is ρ=1.68×10^-8,Ωm. Calculate the resistance of the wire. easy 2 marks Resistance of a conductor
• 34 A copper wire has a length of 3.2 m and a cross‑sectional area of 0.7 mm². The resistivity of copper at 20°C is 1.68×10^-8 Ωm. Calculate the resistance of the wire. easy 3 marks Resistance calculation using resistivity
• 35 A 1.5 m nichrome wire has a cross‑sectional area of 0.6 mm² and a resistivity of 1.10×10^-6 Ωm at 20°C. What is its resistance? hard MCQ 4 marks Resistance of a wire from resistivity