NEET Current Electricity — Set 19

Question 1

Two cells of emf $ 3 \, \text{V} $ and $ 6 \, \text{V} $ with internal resistances $ 1 \, \Omega $ and $ 2 \, \Omega $ are connected in series. What is the equivalent emf?

Accepted Answer

For series: $ \varepsilon_{\text{eq}} = \varepsilon_1 + \varepsilon_2 = 3 + 6 = 9 \, \text{V} $.

Question 2

In a circuit with two identical cells connected in series, if one cell’s polarity is reversed, what happens to the total emf?

Accepted Answer

For two identical cells with emf $ \varepsilon $, in series, total emf = $ \varepsilon + \varepsilon = 2\varepsilon $. If one is reversed, it becomes $ \varepsilon - \varepsilon = 0 $, as the emfs cancel out.

Question 3

A copper wire carries $ 3.4 \, \text{A} $ with a drift speed of $ 1.0 \times 10^{-4} \, \text{m/s} $. If $ n = 8.5 \times 10^{28} \, \text{m}^{-3} $ and $ e = 1.6 \times 10^{-19} \, \text{C} $, what is the cross-sectional area?

Accepted Answer

Drift speed: $ v_d = \frac{I}{n e A} $. Rearrange: $ A = \frac{I}{n e v_d} $. Substitute: $ A = \frac{3.4}{8.5 \times 10^{28} \times 1.6 \times 10^{-19} \times 1.0 \times 10^{-4}} $. Calculate: $ A = \frac{3.4}{1.36 \times 10^5} \approx 2.5 \times 10^{-5} \, \text{m}^2 $.

NEET Physics: Current Electricity — Practice Set 19

Q1. Two cells of emf \( 3 \, \text{V} \) and \( 6 \, \text{V} \) with internal resistances \( 1 \, \Omega \) and \( 2 \, \Omega \) are connected in series. What is the equivalent emf?

Q2. In a circuit with two identical cells connected in series, if one cell’s polarity is reversed, what happens to the total emf?

Q3. A copper wire carries \( 3.4 \, \text{A} \) with a drift speed of \( 1.0 \times 10^{-4} \, \text{m/s} \). If \( n = 8.5 \times 10^{28} \, \text{m}^{-3} \) and \( e = 1.6 \times 10^{-19} \, \text{C} \), what is the cross-sectional area?

Q4. A \( 9 \, \text{V} \) battery with \( 1 \, \Omega \) internal resistance is connected to a \( 8 \, \Omega \) resistor. What is the power dissipated in the internal resistance?

Q5. Two cells in parallel have emf \( 8 \, \text{V} \) and \( 4 \, \text{V} \) with internal resistances \( 2 \, \Omega \) and \( 1 \, \Omega \). What is the equivalent internal resistance?

Q6. In a conductor, if the electric field is suddenly doubled while keeping the conductor's properties unchanged, what happens to the drift velocity of electrons?

Q7. In a circuit with resistors in parallel, why does the total resistance decrease compared to the smallest individual resistance?

Q8. Why does the terminal voltage of a battery become equal to its emf when no current flows?

Q9. Two cells of emf \( 4 \, \text{V} \) and \( 6 \, \text{V} \) with internal resistances \( 1 \, \Omega \) and \( 2 \, \Omega \) respectively are connected in series. What is the equivalent emf and internal resistance of the combination?

Q10. Why does a conductor’s resistance remain finite even when its length approaches zero?