Free Current Electricity MCQs with Answers
1,052 Current Electricity MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Steady current relates charge flow to potential difference, resistance and resistivity, including how temperature changes a conductor's resistance. Sources with internal resistance have terminal voltage below their emf when delivering current, and maximum power output occurs under a specific load condition rather than at zero resistance.
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- A. 4 ms-¹
- B. 0.4 ms-¹
- C. 4 cms-¹
- D. 0.4 mms-¹
Explanation: The drift velocity (vd) is given by the formula I = n A vd e, where I is current, n is electron density, A is area, and e is electron…
Correct answer: 0.4 mms-¹- A. 18 hp
- B. 19 hp
- C. 17 hp
- D. 13500 hp
Explanation: First, calculate the power in watts using P = I²R = 30 A² × 15 Ω = 13,500 W.
Correct answer: 18 hp- A. 3V
- B. 1V
- C. 5V
- D. 10V
Explanation: First, find the total charge that passed: Q = I × t = 3 A × (5 × 60 s) = 900 C.
Correct answer: 1V- A. 2.5 A
- B. 5.0 A
- C. 7.5 A
- D. 10 A
Explanation: The total power drawn by the appliances is Ptotal = 1500 W + 500 W = 2000 W.
Correct answer: 10 A- A. Current and voltage
- B. Resistance and voltage
- C. Charge and voltage
- D. Current and resistance
Explanation: Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage applied across its ends, provided…
Correct answer: Current and voltage- A. Decrease by a factor of 4
- B. Decrease by a factor of 2
- C. Remain unchanged
- D. Increase by a factor of 2
Explanation: According to Ohm's Law (I = V/R), current is directly proportional to voltage when resistance is constant.
Correct answer: Increase by a factor of 2- A. Energy = (current)² x resistance x time
- B. Power = (current)² x resistance
- C. Potential difference = current x resistance
- D. Resistivity = resistance x area + length
Explanation: Resistance (R) is defined as the ratio of the potential difference (V) across a component to the current (I) flowing through it.
Correct answer: Potential difference = current x resistance- A. Length = 100 cm, diameter = 1 mm
- B. Length = 200 cm, diameter = 2 mm
- C. Length = 50 cm, diameter = 0.5 mm
- D. Length = 300 cm, diameter = 3 mm
Explanation: Resistance is given by R = ρL/A, where A is proportional to the diameter squared.
Correct answer: Length = 50 cm, diameter = 0.5 mm- A. 2R
- B. R/2
- C. R
- D. R/4
Explanation: Resistance R is proportional to L/A, and area A is proportional to D². The new resistance R' will have a factor of 4 from the length and a…
Correct answer: R- A. Will become half
- B. Will remain the same
- C. Will be doubled
- D. Will become four times
Explanation: Resistance is given by R = ρL/A. If the new length is L' = 2L and the new area is A' = 2A, the new resistance is R' = ρ(2L)/(2A) = ρL/A =…
Correct answer: Will remain the same- A. Copper wire
- B. Diode
- C. Carbon resistance
- D. Silver wire
Explanation: Non-ohmic devices do not have a constant resistance; their voltage-current relationship is not linear.
Correct answer: Diode- A. 4.4 x 10^-6 Ωm
- B. 1.1 x 10^-6 Ωm
- C. 2.2 x 10^-6 Ωm
- D. 0.22 x 10^-6 Ωm
Explanation: Use the formula for resistivity, ρ = RA/L. First, convert all units to SI: L=1m, diameter=0.002m (so radius r=0.001m), and Area A=πr².
Correct answer: 2.2 x 10^-6 Ωm153. A wire of resistance R is stretched uniformly four times its length. Its new resistance will be:
- A. 16R
- B. 4R
- C. R/4
- D. R/16
Explanation: When a wire is stretched, its volume remains constant. If the length becomes 4L, the cross-sectional area must become A/4.
Correct answer: 16R154. The resistance of a wire is 10 Ω. What is the new resistance if the length of the wire is doubled?
- A. 20 Ω
- B. 40 Ω
- C. 1/2 Ω
- D. 1/4 Ω
Explanation: Assuming the wire is simply replaced by one twice as long with the same area and material, resistance is directly proportional to length.
Correct answer: 20 Ω- A. Increases, increases
- B. Decreases, decreases
- C. Increases, decreases
- D. Decreases, increases
Explanation: Copper (Cu) is a conductor, and its resistance decreases as the temperature decreases due to fewer lattice vibrations.
Correct answer: Decreases, increases- A. 0.4 ohm
- B. 0.8 ohm
- C. 0.6 ohm
- D. 1.0 ohm
Explanation: Assuming the wire's cross-sectional area and material remain the same, resistance is directly proportional to its length.
Correct answer: 0.4 ohm- A. V > ε
- B. V = ε
- C. V < ε
- D. V = 0
Explanation: The equation V = ε - Ir describes the terminal voltage. If the internal resistance (r) is zero, the term Ir becomes zero, regardless of…
Correct answer: V = ε- A. 2A
- B. 2.5 A
- C. 2.2 A
- D. None of above
Explanation: Set up two equations using V = E - Ir for the two conditions to solve for the battery's EMF (E) and internal resistance (r).
Correct answer: 2A- A. Infinite
- B. Very low
- C. Zero
- D. Very high
Explanation: An ideal current source is a theoretical device that delivers a constant current regardless of the voltage across it.
Correct answer: Infinite- A. Current
- B. Energy
- C. Charge
- D. Power
Explanation: A source of EMF, like a battery or generator, does not create charge but provides the energy to move existing charges through a circuit.
Correct answer: Energy