NEET Physics Tutor Doubt 7 - Very Special NEET Physics Questions

Question 1. A set of n equal resistors, each of value R, are connected in parallel to a battery of emf E and internal resistance R. The current drawn is I. Now the n resistors are connected in series to the same battery. If the current becomes I/9, the value of n is

1. 3
2. 18
3. 9
4. 6

Question 2. The resistance of a wire is R ohm. It is melted and then stretched to three times its original length. The new resistance is

1. 3R
2. 9R
3. R3
4. R9

Question 3. The potential difference (V_P − V_Q) between points P and Q in the circuit shown is

1. 4 V
2. −2 V
3. +2 V
4. Zero

Question 4. Two metal wires of identical dimensions are connected in parallel. Their conductivities are σ and 2σ respectively. The effective conductivity of the combination is

1. 3σ2
2. σ2
3. 2σ3
4. σ

Question 5. A uniform wire of resistance 20 Ω has resistance per unit length 1 Ω/m and is bent in the adjoining circular form. If the equivalent resistance between M and N is 1.8 Ω, the length of the shorter section is

1. 2 m
2. 5 m
3. 18 m
4. 1.8 m

Question 6. When a battery is connected across a 16 Ω resistor, the voltage across the resistor is 12 V. When the same battery is connected across a 10 Ω resistor, the voltage across it is 11 V. The internal resistance of the battery is

1. 107 Ω
2. 207 Ω
3. 257 Ω
4. 157 Ω

Question 7. In a meter bridge set-up with null deflection in the galvanometer as shown, the value of the unknown resistor R is

1. 80 Ω
2. 100 Ω
3. 160 Ω
4. 120 Ω

Question 8. In the potentiometer circuit shown, the balance length AP = 70 cm when switch S is open. When S is closed and R = 6 Ω, the balance length AP′ = 60 cm. The internal resistance of the cell C′ is

1. 2 Ω
2. 1.5 Ω
3. 1 Ω
4. 0.5 Ω

Question 9. When 115 V is applied across a wire that is 10 m long and has a radius of 0.30 mm, the current density is 1.4 × 10⁴ A/m². The resistivity of the wire is

1. 2.0 × 10⁴ Ωm
2. 4.1 × 10⁻⁴ Ωm
3. 8.2 × 10⁻⁴ Ωm
4. 2.0 × 10⁻³ Ωm

Question 10. Two electric lamps of 60 watt each are connected in parallel. The power consumed by the combination will be, assuming the same source voltage,

1. 80 watt
2. 120 watt
3. 60 watt
4. 30 watt

Question 11. In the circuit shown, the reading of the voltmeter is

1. 2 V
2. 2.5 V
3. 3 V
4. 5 V

Question 12. For the balanced bridge shown in the figure, the current through the 2 Ω resistance is

1. 227 A
2. 137 A
3. 167 A
4. 207 A

Question 13. The V-I graph for a conductor at two temperatures T₁ and T₂ is shown. The relation between the temperatures is

1. T₁ > T₂
2. T₁ < T₂
3. T₁ = T₂
4. T₁ = 1/T₂

Question 14. In the network shown, the potential difference between A and B is

1. 2 V
2. 6 V
3. 4 V
4. 1 V

Question 15. A potentiometer wire of length 100 cm has resistance 10 Ω. It is connected in series with a 5 Ω resistance and an accumulator of emf 6 V. A source of 2.4 V is balanced against length L of the potentiometer wire. The value of L is

1. 40 cm
2. 30 cm
3. 50 cm
4. 60 cm

Question 16. In a metre bridge, the resistance in the left gap and the right gap are in the ratio 2 : 3. The balance point from the left end is

1. 60 cm
2. 50 cm
3. 40 cm
4. 20 cm

Question 17. A resistor R and a 10 Ω resistor are connected in parallel across a 20 V source. If the total power consumed is 50 W, the value of R is

1. 20 Ω
2. 10 Ω
3. 30 Ω
4. 40 Ω

Question 18. Consider the statements: (A) Kirchhoff’s junction law follows from conservation of energy. (B) Kirchhoff’s loop law follows from conservation of charge. Which option is correct?

1. Both statements are correct
2. Both statements are incorrect
3. A is correct but B is incorrect
4. A is incorrect but B is correct

Question 19. Two batteries of emf 2 V and 3 V with internal resistances 1 Ω and 2 Ω respectively are connected in parallel. The effective emf is

1. 53 V
2. 73 V
3. 43 V
4. 5 V

Question 20. The rate of flow of charge through a metallic conductor of non-uniform cross-section is uniform. Which quantity remains constant along the conductor?

1. Current
2. Current density
3. Electric potential
4. Electric field

Question 21. When the temperature of a conductor is increased, its resistance increases because

1. relaxation time increases
2. mass of electron increases
3. electron density decreases
4. relaxation time decreases

Question 22. In the circuit shown, the ammeter reading is

1. 0.4 A
2. 0.8 A
3. 0.2 A
4. 0.6 A

Question 23. Three parallel straight wires are perpendicular to the plane of paper and carry equal currents I in the same direction. They are placed at the vertices of an equilateral triangle of side d. The force per unit length on wire A is

1. μ₀I²√2 πd
2. √3 μ₀I²2πd
3. μ₀I²2πd
4. μ₀I²πd

Question 24. A wire carrying current is bent into a circular loop of one turn and the magnetic field at its centre is B. If the same wire is bent into a circular coil of four turns, the magnetic field at the centre becomes

1. 4B
2. B4
3. 16B
4. B8

Question 25. A charged particle enters a uniform magnetic field. Its kinetic energy

1. decreases
2. increases
3. becomes zero
4. remains constant

Question 26. An arc of a circle of radius R subtends an angle π/3 at the centre and carries current I. The magnetic field at the centre is

1. μ₀I12R
2. μ₀I6R
3. μ₀I4R
4. μ₀I3R

Question 27. A wire carrying current 2I and another wire carrying current 3I in the opposite direction produce magnetic field B at the midpoint as shown. What will be the field at the midpoint when the 2I wire is switched off?

1. 3B5
2. 2B5
3. 2B3
4. 4B3

Question 28. An electric field 1200 ĵ V/m and a magnetic field 0.20 k̂ Wb/m² act on a moving electron. The electron will move with uniform speed, without deflection, when its speed is

1. 3.0 × 10⁶ m/s
2. 6.0 × 10³ m/s
3. 4.0 × 10⁷ m/s
4. 2.0 × 10⁸ m/s

Question 29. A long hollow copper tube carries a uniform current I. Which statement is true?

1. Magnetic field B is zero at all points inside the tube.
2. Magnetic field B is zero only at the point on the axis of the tube.
3. Magnetic field is maximum at points on the axis of the tube.
4. Magnetic field is zero at any point outside the tube.

Question 30. For the current-carrying wire shown, the magnetic field induction at point O is

1. μ₀I4R
2. μ₀I4R(1/π + 1)
3. μ₀I4R(1 − 1/π)
4. Zero

Question 31. The magnetic force on a charged particle of charge −4 μC moving in a magnetic field of 1 T in the y-direction with velocity (3 î + 4 ĵ) × 10⁶ m/s is

1. 6 N in y-direction
2. 12 N in negative z-direction
3. 8 N in z-direction
4. 4 N in negative y-direction

Question 32. A wire of length 4 m carrying a current of 2 A is bent into a circle. Its magnetic moment is

1. 4π A m²
2. 4π A m²
3. 8π A m²
4. 2π A m²

Question 33. The correct graph between magnetic moment M of a current-carrying loop and its radius r is

1. Decreasing curve
2. Constant graph
3. Increasing parabolic graph
4. Increasing straight-line graph

Question 34. Two α-particles have velocities in the ratio 4 : 3 and enter a magnetic field. If they move in different circular paths, the ratio of their radii is

1. 1 : 2
2. 4 : 3
3. 16 : 9
4. 9 : 16

Question 35. A 4 cm long wire carrying a current of 5 A is placed inside a solenoid perpendicular to its axis. If the magnetic field inside the solenoid is 0.4 T, the magnetic force on the wire is

1. 4 × 10⁻² N
2. 0.4 N
3. 8 × 10⁻² N
4. 0.8 N

Question 36. A charged particle moves in a transverse magnetic field. If its velocity is doubled, the radius of its circular path becomes

1. doubled
2. halved
3. increased by four times
4. unchanged

Question 37. A voltmeter measuring 4 V is constructed with a galvanometer of resistance 16 Ω and full-scale current 2 mA. The value of series resistance R is

1. 898 Ω
2. 1984 Ω
3. 2280 Ω
4. 2598 Ω

Question 38. If the current sensitivity of a galvanometer is doubled by increasing the number of turns, its voltage sensitivity will be

1. doubled
2. halved
3. four times
4. unchanged

Question 39. A current-carrying loop is placed in a uniform magnetic field. The torque on the loop does not depend upon

1. area of loop
2. value of current
3. magnetic field
4. none of these

Question 40. The power supplied by the magnetic force on a moving charged particle is

1. always zero
2. never zero
3. zero only when v ⟂ B
4. zero only when v ∥ B

Question 41. A thin disc of radius R and mass M has charge q uniformly distributed on it. It rotates with angular velocity ω. The magnetic moment of the disc about the axis of rotation will be

1. qR²ω4
2. qR²ω2
3. 3qR²ω4
4. qR²ω3

Question 42. The magnetic field at point P due to the current-carrying circular coil shown, of radius a with P at axial distance √3a, is

1. μ₀I8a
2. μ₀I4a
3. μ₀I16a
4. 3μ₀I4a

Question 43. Ampere’s circuital law can be derived from

1. Ohm’s law
2. Biot-Savart’s law
3. Kirchhoff’s law
4. Gauss’s law

Question 44. A proton enters a region of uniform magnetic field 1 T with velocity u at an angle 37° with B. If P is the pitch of the helical path followed, the radius of the helix is

1. Pπ
2. 3P8π
3. 2P3π
4. 3P4π

Question 45. A long solenoid has n turns per unit length and current I ampere is flowing through it. The magnetic field at the end of the solenoid will be

1. 8μ₀nI
2. 2μ₀n²I
3. μ₀nI2
4. μ₀n²I