Electricity — Set 3
Physics · विद्युत · Questions 21–30 of 60
A device that allows current mainly in one direction is called?
Correct Answer: A. Diode
A diode is designed to conduct primarily in one direction. It is made using a p-n junction. Diodes are used in rectifiers to convert AC to DC.
Two resistors 3 Ω and 6 Ω are connected in parallel. What is the equivalent resistance?
Correct Answer: B. 9 Ω
For two resistors in parallel, Req = (R1R2)/(R1+R2). Substituting 3 and 6 gives Req = 18/9 = 2 Ω. Parallel combination always gives a value less than the smallest resistor.
Kirchhoff’s current law (KCL) states that at a junction?
Correct Answer: D. Power is conserved in each branch
The correct answer is 'Power is conserved in each branch'. KCL is based on conservation of charge. The algebraic sum of currents at a node is zero. It means current entering a junction equals current leaving it.
The SI unit of capacitance is?
Correct Answer: B. Henry
The correct answer is 'Henry'. Capacitance is defined by C = Q/V. Its SI unit is farad (F). A farad is a very large unit, so microfarad and picofarad are common.
A capacitor stores 12 μC charge at 3 V. What is its capacitance?
Correct Answer: D. 36 μF
Use C = Q/V. Substituting Q = 12 μC and V = 3 gives C = 12/3 = 4 μF. Capacitance measures how much charge is stored per volt.
Inserting a dielectric between capacitor plates generally?
Correct Answer: A. Reverses polarity
The correct answer is 'Reverses polarity'. A dielectric reduces the effective electric field inside the capacitor. This allows more charge to be stored for the same voltage. Therefore the capacitance increases by the dielectric constant factor.
A circuit draws 2 A from a 12 V battery. What is the electrical power used?
Correct Answer: D. 10 W
Use P = VI. Substituting V = 12 and I = 2 gives P = 24 W. Power is the rate at which electrical energy is used.
For a sinusoidal AC, the RMS value of voltage is?
Correct Answer: D. Vrms = V0
RMS value gives the equivalent DC value for the same heating effect. For a sine wave, Vrms = V0/√2 where V0 is peak voltage. The same relation holds for current as Irms = I0/√2.
Earthing in electrical wiring is used mainly to?
Correct Answer: A. Make appliances consume less power
The correct answer is 'Make appliances consume less power'. Earthing provides a safe path for leakage current. It helps prevent electric shock by keeping the appliance body near ground potential. Proper earthing supports protective devices like fuses and breakers.
Resistors 2 Ω, 3 Ω, and 5 Ω are in series. What is the equivalent resistance?
Correct Answer: D. 1/10 Ω
In series, resistances add directly. So Req = 2 + 3 + 5 = 10 Ω. Series connection increases the total resistance.