Electricity — Set 6
Physics · विद्युत · Questions 51–60 of 60
In alternating current (AC), the direction of current?
Correct Answer: C. Remains constant
AC changes direction with time in a periodic manner. That is why its instantaneous value can be positive or negative. Household supply is commonly AC for efficient voltage transformation.
Power factor in an AC circuit is equal to?
Correct Answer: C. cosφ
Power factor is the cosine of the phase angle between voltage and current. It is written as cosφ and lies between 0 and 1 in typical circuits. A higher power factor means more useful power for the same current.
An AC circuit has Vrms = 100 V, Irms = 2 A, and power factor 0.8. What is the average power?
Correct Answer: D. 80 W
Average power in AC is P = Vrms Irms cosφ. Substituting 100, 2, and 0.8 gives P = 100×2×0.8 = 160 W. Power factor accounts for phase difference in reactive circuits.
The unit commonly used in household electricity bills for energy is?
Correct Answer: C. Watt
Electrical energy for billing is commonly measured in kilowatt-hour. One unit of electricity generally means 1 kWh. This equals 3.6×10^6 joules.
Fleming’s left-hand rule is used to find the direction of?
Correct Answer: C. Force on a current-carrying conductor in a magnetic field
Fleming’s left-hand rule applies to the motor effect. It gives the direction of force on a conductor carrying current in a magnetic field. The right-hand rule is used for the generator effect.
Two capacitors 3 μF and 6 μF are connected in series. What is the equivalent capacitance?
Correct Answer: A. 2 μF
For series capacitors, 1/Ceq = 1/C1 + 1/C2. Substituting 3 and 6 gives 1/Ceq = 1/3 + 1/6 = 1/2, so Ceq = 2 μF. Series combination reduces capacitance below the smallest capacitor.
A superconductor below its critical temperature has?
Correct Answer: A. Infinite capacitance
A superconductor shows zero resistivity below a critical temperature. That means current can flow without energy loss due to resistance. Superconductivity is a quantum phenomenon seen in certain materials.
Two capacitors 2 μF and 5 μF are connected in parallel. What is the equivalent capacitance?
Correct Answer: D. 1.4 μF
In parallel, capacitances add directly. So Ceq = 2 + 5 = 7 μF. Parallel combination increases capacitance.
The permittivity of free space is denoted by ɛ0 and is approximately?
Correct Answer: B. 8.85×10^-12 C^2/(N m^2)
Permittivity describes how electric fields behave in vacuum. Its approximate value is 8.85×10^-12 C^2/(N m^2). It is related to Coulomb’s constant by k = 1/(4πɛ0).
An appliance uses 600 W when connected to 200 V. What current does it draw?
Correct Answer: A. 3 A
Use P = VI for electrical power. Substituting P = 600 W and V = 200 V gives I = 600/200 = 3 A. Higher power at the same voltage means higher current.