Electricity — Set 5
Physics · विद्युत · Questions 41–50 of 60
The value of Coulomb’s constant k in vacuum is approximately?
Correct Answer: A. 3×10^8 m/s
Coulomb’s constant relates force to charges and distance in Coulomb’s law. Its approximate value is 9×10^9 N m^2/C^2. It is related to permittivity by k = 1/(4πɛ0).
1 ampere is equal to?
Correct Answer: A. 1 V/m
Electric current is the rate of flow of charge. So 1 ampere means 1 coulomb of charge per second. This definition matches I = Q/t.
1 kilowatt-hour (kWh) is equal to?
Correct Answer: A. 3.6×10^6 J
Energy in kWh equals power in kW multiplied by time in hours. 1 kWh = 1000 W × 3600 s = 3.6×10^6 J. It is a practical unit for large electrical energy use.
Which color code represents a 1 kΩ resistor (4-band, tolerance ignored)?
Correct Answer: C. Red-Black-Brown
For 1 kΩ, the first two digits are 1 and 0, and the multiplier is 10^2. Brown represents 1, black represents 0, and red represents 10^2. Resistor color codes help identify values without printing numbers.
In a balanced Wheatstone bridge, the correct condition is?
Correct Answer: D. P/Q = S/R
A Wheatstone bridge is balanced when the ratio of two resistances equals the ratio of the other two. The condition is P/Q = R/S, which makes the galvanometer current zero. This method helps measure an unknown resistance accurately.
A cell has emf 1.5 V and internal resistance 0.5 Ω. If current is 1 A, what is the terminal voltage?
Correct Answer: B. 2.0 V
Terminal voltage is V = E - Ir for a discharging cell. Substituting E = 1.5, I = 1, and r = 0.5 gives V = 1.5 - 0.5 = 1.0 V. Internal resistance causes a drop in terminal voltage under load.
For capacitors C1 and C2 in series, the equivalent capacitance is?
Correct Answer: A. Ceq = C1 + C2
In series, capacitors share the same charge but divide voltage. Therefore the reciprocals add: 1/Ceq = 1/C1 + 1/C2. Series combination gives a capacitance smaller than the smallest capacitor.
A capacitor of 2 μF is charged to 10 V. What energy is stored in it?
Correct Answer: C. 1×10^-3 J
Energy in a capacitor is U = (1/2)CV^2. Substituting C = 2×10^-6 and V = 10 gives U = 0.5×2×10^-6×100 = 1×10^-4 J. Capacitors store energy in their electric field.
Electrical conductivity (σ) is related to resistivity (ρ) by?
Correct Answer: B. σ = ρ^2
Conductivity measures how easily current flows in a material. It is the reciprocal of resistivity, so σ = 1/ρ. Metals have high conductivity and low resistivity.
A wire has R0 = 10 Ω at 0°C and temperature coefficient α = 0.004/°C. What is its resistance at 50°C?
Correct Answer: D. 20 Ω
Use R = R0(1 + αΔT). Substituting R0 = 10, α = 0.004, and ΔT = 50 gives R = 10(1 + 0.2) = 12 Ω. For many metals, resistance increases with temperature.