NEET Current Electricity — Set 1

Question 1

A Wheatstone bridge has $ R_1 = 14 \, \Omega $, $ R_2 = 28 \, \Omega $, $ R_3 = 10 \, \Omega $. What is $ R_4 $ for balance?

Accepted Answer

Balance condition: $ \frac{R_1}{R_2} = \frac{R_3}{R_4} $. Substitute: $ \frac{14}{28} = \frac{10}{R_4} $. Solve: $ 0.5 = \frac{10}{R_4} \Rightarrow R_4 = \frac{10}{0.5} = 20 \, \Omega $.

Question 2

A $ 16 \, \text{V} $ battery with $ 2 \, \Omega $ internal resistance delivers a current of $ 2 \, \text{A} $ to a resistor. What is the resistance of the resistor?

Accepted Answer

Terminal voltage: $ V = \varepsilon - I r = 16 - 2 \times 2 = 12 \, \text{V} $. Resistance: $ R = \frac{V}{I} = \frac{12}{2} = 6 \, \Omega $.

Question 3

What ensures that the total voltage drop across a series circuit equals the source voltage?

Accepted Answer

Kirchhoff’s loop rule (conservation of energy) ensures that the sum of potential drops across all elements in a closed loop equals the supplied voltage, as energy is conserved in the circuit.

NEET Physics: Current Electricity — Practice Set 1

Q1. A Wheatstone bridge has \( R_1 = 14 \, \Omega \), \( R_2 = 28 \, \Omega \), \( R_3 = 10 \, \Omega \). What is \( R_4 \) for balance?

Q2. A \( 16 \, \text{V} \) battery with \( 2 \, \Omega \) internal resistance delivers a current of \( 2 \, \text{A} \) to a resistor. What is the resistance of the resistor?

Q3. What ensures that the total voltage drop across a series circuit equals the source voltage?

Q4. What causes the potential difference across a resistor to drop when current flows through it?

Q5. A conductor has a resistivity of \( 4 \times 10^{-8} \, \Omega \text{m} \) at \( 20^\circ \text{C} \) and a temperature coefficient of \( 4 \times 10^{-3} \, ^\circ\text{C}^{-1} \). What is its resistivity at \( 60^\circ \text{C} \)?

Q6. A wire of length \( 2 \, \text{m} \) and resistance \( 4 \, \Omega \) is stretched to \( 4 \, \text{m} \). What is the new resistance?

Q7. What causes the resistivity of a conductor to deviate from Ohm’s law at very high electric fields?

Q8. Why does the resistance of a metallic conductor increase with temperature?

Q9. In a circuit with a battery and a resistor, if the internal resistance of the battery equals the external resistance, what fraction of the total power is dissipated in the external resistor?

Q10. A nichrome wire has a resistance of \( 60 \, \Omega \) at \( 30^\circ \text{C} \) and \( \alpha = 1.7 \times 10^{-4} \, ^\circ\text{C}^{-1} \). What is its resistance at \( 330^\circ \text{C} \)?