A capacitor holding 100 μC discharges through a resistor. Approximately what charge remains after a time equal to two time constants?
Correct answer D. 14 μC
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MDCAT ECAT Physics MCQs
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An uncharged capacitor is connected in series with a 4.0 kΩ resistor to a 12 V battery. What is the current at the instant the switch is closed?
Correct answer D. 3.0 mA
A large plane sheet carries a uniform surface charge density of 1.77 × 10⁻⁸ C/m². What is the electric field near it (ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²)?
Correct answer B. 1.0 × 10³ N/C
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Two large parallel plates carry equal and opposite charge densities of magnitude 8.85 × 10⁻⁸ C/m². What is the electric field between them (ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²)?
Correct answer B. 1.0 × 10⁴ N/C
Two large parallel plates carry equal and opposite uniform charges. What is the electric field in the region outside the plates?
Correct answer D. Zero
Electric potential at a point is the work done per unit positive charge in bringing a charge from infinity to that point. Its SI unit, the volt, is equivalent to ____.
Correct answer A. J C⁻¹
What is the electric potential at a distance of 0.30 m from a point charge of 6.0 nC (k = 9.0 × 10⁹ N m² C⁻²)?
Correct answer B. 180 V
How much work is needed to move a charge of 2.0 μC between two points whose potential difference is 150 V?
Correct answer D. 3.0 × 10⁻⁴ J
An electron is accelerated from rest through a potential difference of 500 V. What kinetic energy does it gain (e = 1.6 × 10⁻¹⁹ C)?
Correct answer A. 8.0 × 10⁻¹⁷ J
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Equal and opposite charges +q and −q are a short distance apart. At the midpoint between them, ____.
Correct answer C. the potential is zero but the field is not zero
A potential difference of 250 V is applied across two parallel plates 5.0 mm apart. What is the electric field between them?
Correct answer C. 5.0 × 10⁴ V/m
In a circuit where a capacitor charges through a resistor, the time constant RC is the time taken for the capacitor to reach about ____ of its final charge.
Correct answer C. 63%
A 5.0 μF capacitor is charged through a 2.0 MΩ resistor. What is the time constant of the circuit?
Correct answer A. 10 s
What is the magnitude of the electric field at 0.20 m from a point charge of 4.0 nC in air (k = 9.0 × 10⁹ N m² C⁻²)?
Correct answer D. 9.0 × 10² N/C
What is the magnitude of the force on an electron in a uniform electric field of 2.0 × 10⁴ N/C (e = 1.6 × 10⁻¹⁹ C)?
Correct answer A. 3.2 × 10⁻¹⁵ N
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Two equal positive point charges are separated by a distance d. What is the electric field at the midpoint between them?
Correct answer D. Zero
Charges of +2.0 μC and −2.0 μC are 0.20 m apart in air. What is the electric field at the midpoint between them (k = 9.0 × 10⁹ N m² C⁻²)?
Correct answer C. 3.6 × 10⁶ N/C
Point charges +1.0 μC and +4.0 μC are 0.30 m apart. At what distance from the +1.0 μC charge, on the line joining them, is the electric field zero?
Correct answer B. 0.10 m
Why can two electric field lines never cross each other?
Correct answer B. The field at the crossing point would have two directions
Electric field lines due to a system of charges ____.
Correct answer A. start on positive charges and end on negative charges