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JEE Main Current Electricity — practice questions — page 2

Explore 100 free Current Electricity questions in JEE Main Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Current Electricity questions and exercises with answers

Showing questions 31–60 of 100.

Two batteries with emf E₁ = 4V (r₁ = 1Ω) and E₂ = 6V (r₂ = 2Ω) in parallel. Find equivalent emf:Read the answer and worked solution →A wire of resistance 10 Ω is stretched to double its length without changing volume. Its new resistance:Read the answer and worked solution →Maximum power transfer from a source occurs when external resistance equals:Read the answer and worked solution →In a meter bridge experiment, the null point divides the wire as 30 cm and 70 cm. If known resistance is 6 Ω, the unknown is:Read the answer and worked solution →If a conductor of length l and cross-sectional area A has resistivity ρ, halving the length AND halving the area gives new resistanceRead the answer and worked solution →The drift velocity of electrons in a copper wire carrying steady current is of the order ofRead the answer and worked solution →A cell of emf ε and internal resistance r is connected to an external resistance R. The maximum power delivered to R isRead the answer and worked solution →In a Wheatstone bridge, arms have resistances P, Q, R, S in cyclic order with a galvanometer between the P-Q and R-S junctions. The bridge is balanced whenRead the answer and worked solution →A potentiometer of length L is used to compare emfs. If the balance lengths for cells of emf ε₁ and ε₂ are l₁ and l₂ respectively, then ε₁ / ε₂ equalsRead the answer and worked solution →Two cells of emf ε and internal resistance r each are connected in parallel. The equivalent emf and internal resistance areRead the answer and worked solution →Kirchhoff current law at a junction is a statement ofRead the answer and worked solution →A wire has a resistance R. It is stretched uniformly so that its length becomes 2L. The new resistance isRead the answer and worked solution →The relation between current density j, drift velocity v_d, number density n and charge e for a metallic conductor isRead the answer and worked solution →For a battery of emf ε and internal resistance r driving current I through external resistance R, the terminal voltage V equalsRead the answer and worked solution →True or false: what emf actually isRead the answer and worked solution →Complete the statement of Ohm's lawRead the answer and worked solution →Tap every way Ohm's law can failRead the answer and worked solution →Match each device or material to its behaviourRead the answer and worked solution →Sort each material by its resistivityRead the answer and worked solution →Complete the resistance relationRead the answer and worked solution →True or false: resistance and resistivityRead the answer and worked solution →Match each of Kirchhoff's rules to what it conservesRead the answer and worked solution →Kirchhoff's rulesRead the answer and worked solution →Order the steps: find an unknown resistance with a Wheatstone bridgeRead the answer and worked solution →True or false: internal resistanceRead the answer and worked solution →Which quantity is which?Read the answer and worked solution →Assertion and reasonRead the answer and worked solution →Charge carriersRead the answer and worked solution →Two are true, one is notRead the answer and worked solution →Three of these are wrong. Find the one that holds.Read the answer and worked solution →

Worked practice questions

Two batteries with emf E₁ = 4V (r₁ = 1Ω) and E₂ = 6V (r₂ = 2Ω) in parallel. Find equivalent emf:

  1. 3.33 V
  2. 10 V
  3. 4.67 V
  4. 5 V
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Correct answer: C. 4.67 V

For parallel: E = (E₁/r₁ + E₂/r₂)/(1/r₁ + 1/r₂) = (4/1 + 6/2)/(1/1 + 1/2) = (4 + 3)/(1.5) = 7/1.5 ≈ 4.67 V.

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A wire of resistance 10 Ω is stretched to double its length without changing volume. Its new resistance:

  1. 5 Ω
  2. 40 Ω
  3. 80 Ω
  4. 20 Ω
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Correct answer: B. 40 Ω

Volume V = lA = constant. When l doubles, A halves. R_new = ρ(2l)/(A/2) = 4ρl/A = 4R = 4 × 10 = 40 Ω. **So stretching doubles l → resistance quadruples.**

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Maximum power transfer from a source occurs when external resistance equals:

  1. Zero
  2. Equal to internal r
  3. Twice internal r
  4. Half of internal r
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Correct answer: B. Equal to internal r

**Maximum power transfer theorem:** when R_external = R_internal (= r), the power dissipated in the external load is maximised. At this point, efficiency is 50% (half power in load, half in internal resistance).

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