NEET Physics: Electric Circuits questions with solutions

Q1. A moving coil ammeter requires a potential difference of \( 0.4 V \) across it for full scale deflection. It has fixed shunt resistance of 0.01 ohm with a coil circuit resistance of \( \boldsymbol{R}=\mathbf{1} \boldsymbol{k} \) ohm. The value of shunt required to give full scale deflection when the total current is \( 10 A \) is equal to

1. 0.02 ohm
2. 0.04 ohm
3. 0.05 ohm
4. 0.06 ohm

Answer: 0.02 ohm

The coil needs 0.4 V for full-scale deflection, so its current is set by its resistance. The remaining current out of the 10 A total must flow through the shunt, and since both branches share the same voltage, the shunt resistance follows from Ohm’s law.

Q2. Potentiometer measures potential more accurately because

1. it measures potential in the open circuit
2. it uses sensitive galvanometer for null deflection
3. it uses high resistance potentiometer wire
4. it measures potential in the closed circuit

Answer: it measures potential in the open circuit

A potentiometer compares voltages under null condition, so no current is drawn from the source being measured. Because there is no loading effect, the measured potential difference equals the true open-circuit value.

Q3. There are a large number of cells available, each marked \( (6 V, 0.5 \Omega) \) to be used to supply current to a device of resistance \( 0.75 \Omega, \) requiring \( 24 A \) current. How should the cells be arranged, so that power is transmitted to the load using minimum number of cells?

1. Six rows, each containing four cells
2. Four rows, each containing six cells
3. Four rows, each containing four cells
4. Six rows, each containing Six cells

Answer: Six rows, each containing four cells

The load needs 24 A through 0.75 Ω, so it must receive 18 V. Each cell is 6 V with 0.5 Ω internal resistance, so 3 cells in series give 18 V per string; then the current requirement is met by putting enough such strings in parallel. The minimum-cell arrangement that satisfies both voltage and current is 6 parallel rows of 4 cells in series, totaling 24 cells.

Q4. Four conductors of resistance 4,3,9 and 6 ohm are connected in \( A B, B C, C D \) and DA arms of a Wheatstone bridge. The bridge can be balanced by connecting.

1. \( 1) 6 \) ohm in series with 3 ohm conductor
2. 2) 4 ohm in parallel with 6 ohm conductor
3. 3 ) 3 ohm in series with 3 ohm conductor
4. 4 ) 5 ohm in series with 6 ohm conductor

Answer: 2) 4 ohm in parallel with 6 ohm conductor

A Wheatstone bridge balances when the ratio of one pair of adjacent arms equals the ratio of the other pair. The option that changes the 4 Ω and 6 Ω arms into an equivalent resistance giving the needed ratio is the one with 4 Ω in parallel with 6 Ω.