Electricity — Set 1
Physics · विद्युत · Questions 1–10 of 60
What is the SI unit of electric charge?
Correct Answer: D. Coulomb
Electric charge is measured in coulomb in the SI system. One coulomb is the charge carried by a 1 ampere current in 1 second. Charge is a fundamental quantity in electricity.
Ohm’s law is correctly written as?
Correct Answer: A. V = IR
Ohm’s law states that voltage equals current times resistance. It is written as V = IR for an ohmic conductor at constant temperature. It helps relate V, I, and R in circuits.
A potential difference of 12 V produces a current of 3 A in a resistor. What is the resistance?
Correct Answer: C. 36 Ω
Use Ohm’s law R = V/I. Substituting V = 12 and I = 3 gives R = 12/3 = 4 Ω. Resistance is measured in ohm (Ω).
Two resistors 2 Ω and 3 Ω are connected in series. Their equivalent resistance is?
Correct Answer: C. 0.5 Ω
In series, resistances add directly. So Req = 2 + 3 = 5 Ω. Series connection increases total resistance.
For two resistors R1 and R2 in parallel, the equivalent resistance is?
Correct Answer: C. Req = (R1 + R2)/2
In a parallel combination, 1/Req = 1/R1 + 1/R2. For two resistors, this simplifies to Req = (R1R2)/(R1 + R2). Parallel connection reduces the equivalent resistance below the smallest resistor.
If 12 coulomb of charge flows in 3 seconds, what is the current?
Correct Answer: A. 1 A
Current is charge per unit time, so I = Q/t. Substituting Q = 12 C and t = 3 s gives I = 12/3 = 4 A. The SI unit of current is ampere (A).
Which expression gives electric power in a circuit?
Correct Answer: A. P = R/I
Electric power is the rate of electrical energy transfer. It is given by P = VI when voltage V and current I are known. The SI unit of power is watt (W).
A 100 W appliance runs for 2 hours. How much energy is used in kWh?
Correct Answer: D. 20 kWh
Convert 100 W to kW as 0.1 kW. Energy = power × time = 0.1 × 2 = 0.2 kWh. kWh is widely used for household electrical energy.
The SI unit of resistivity is?
Correct Answer: D. m/Ω
Resistivity is a material property used in R = ρL/A. Its SI unit is ohm-meter (Ω m). Good conductors have low resistivity.
A wire has resistivity 2×10^-7 Ω m, length 5 m, and area 1×10^-6 m^2. What is its resistance?
Correct Answer: A. 0.01 Ω
Use R = ρL/A. Substituting ρ = 2×10^-7, L = 5, and A = 1×10^-6 gives R = (2×10^-7×5)/(1×10^-6) = 1 Ω. Resistance increases with length for the same material and area.