ECAT — Engineering College Admission Test (UET)
Take the ECAT Physics — Electrostatics and Current Electricity (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. Two point charges of 3 μC and 4 μC are 30 cm apart in air. The force between them is
Answer: D. 1.2 N
Explanation: F = kq₁q₂/r² = 9×10⁹ × 12×10⁻¹² / 0.09 = 1.2 N.
Q2. The distance between two charges is tripled. The electrostatic force between them becomes
Answer: B. 1/9 of its value
Explanation: F ∝ 1/r², so tripling r divides F by 9.
Q3. The electric field at a distance of 30 cm from a point charge of 2 nC is
Answer: B. 200 N/C
Explanation: E = kq/r² = 9×10⁹ × 2×10⁻⁹/0.09 = 200 N/C.
Q4. An electron (charge 1.6 × 10⁻¹⁹ C) is placed in a uniform field of 500 N/C. The magnitude of its acceleration is (m = 9.1 × 10⁻³¹ kg)
Answer: B. 8.8 × 10¹³ m/s²
Explanation: a = eE/m = 1.6×10⁻¹⁹ × 500/9.1×10⁻³¹ = 8.8e+13 m/s².
Q5. The electric potential at 30 cm from a 2 nC point charge is
Answer: B. 60 V
Explanation: V = kq/r = 9×10⁹ × 2×10⁻⁹/0.3 = 60 V.
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Q6. A proton is accelerated from rest through a potential difference of 1000 V. Its kinetic energy gained is
Q7. Plates 2 cm apart have a potential difference of 400 V. The magnitude of the uniform field between them is
Q8. The electric flux through a closed surface enclosing a charge of 8.85 nC is (ε₀ = 8.85 × 10⁻¹² C²/N m²)
Q9. Inside a uniformly charged thin spherical shell, the electric field is
Q10. The field of an infinite sheet of charge with surface density σ is
Q11. A parallel-plate capacitor has plate area 0.02 m² and separation 1 mm in air. Its capacitance is approximately
Q12. Capacitors of 6 μF and 3 μF are connected in series across a 90 V supply. The charge on each is
Q13. The energy stored in a 10 μF capacitor charged to 200 V is
Q14. A capacitor is charged and disconnected from the battery, then a dielectric of constant 4 is inserted between the plates. The stored energy
Q15. A 100 μF capacitor discharges through a 2 kΩ resistor. The time constant is
Q16. A current of 0.5 A flows for 2 minutes through a wire. The number of electrons passing a section is (e = 1.6 × 10⁻¹⁹ C)
Q17. A wire of resistance 8 Ω is stretched uniformly to twice its original length. Its new resistance is
Q18. A resistor has resistance 50 Ω at 0 °C and a temperature coefficient of 0.004 °C⁻¹. Its resistance at 50 °C is
Q19. A 6 Ω and a 3 Ω resistor in parallel are connected in series with a 4 Ω resistor. The equivalent resistance is
Q20. A 12 V battery of negligible internal resistance supplies the 6 Ω combination above. The current drawn is
Q21. A cell of emf 1.5 V delivers 1 A to an external resistor and its terminal voltage is 1.2 V. Its internal resistance is
Q22. A battery of emf 10 V and internal resistance 2 Ω is connected to a load for maximum power transfer. The power delivered to the load is
Q23. A 100 W, 220 V bulb is operated on 110 V. Assuming constant resistance, the power consumed is
Q24. A 2 kW heater is used for 5 hours a day for 30 days. If energy costs Rs 20 per kW h, the monthly cost is
Q25. In applying Kirchhoff’s junction rule, the algebraic sum of the currents at a junction is zero. This statement expresses conservation of
Q26. In a balanced Wheatstone bridge, the arms P = 10 Ω, Q = 20 Ω and R = 15 Ω are arranged so that P/Q = R/X. The unknown resistance X is
Q27. A potentiometer wire 1 m long carries a steady current producing 2 V over its length. A cell balances at 60 cm. The emf of the cell is
Q28. Two resistors are joined in parallel across a battery. Compared with the resistor of smaller value, the resistor of larger value
Q29. Millikan’s oil drop experiment showed that
Q30. Two equal positive charges q are placed a distance 2a apart. At the midpoint of the line joining them, the electric field and potential are respectively